L’AMPc est un messager important de la régulation neurohormonale du cœur. En activant ses effecteurs, l’AMPc régule de nombreuses fonctions cellulaires telles que l'expression de gènes, le couplage excitation-contraction et le métabolisme cellulaire. Chez les mammifères, l'AMPc est produit par une famille d’adénylate cyclases au sein de plusieurs compartiments subcellulaires solubles ou membranaires. L'existence et le rôle de la signalisation des nucléotides cycliques dans les mitochondries ont été postulés, mais n'ont pas encore été démontrés. De plus, son implication dans la régulation de la mort cellulaire est encore inconnue. Dans cette thèse, nous avons démontré l'expression locale de plusieurs acteurs de la signalisation de l'AMPc dans les mitochondries cardiaques, à savoir une forme tronquée soluble AC (sACt) et la protéine d'échange directement activées par AMPc 1 (Epac1). Nous avons montré un rôle protecteur pour sACt contre la mort cellulaire, l'apoptose, ainsi que la nécrose de cardiomyocytes primaires. Lors de la stimulation par du bicarbonate (HCO3-) et du Ca2+, la sACt produit de l’AMPc, qui à son tour stimule la consommation d'oxygène, une augmentation du potentiel mitochondrial de membrane (ΔΨm) et la production d'ATP. L’AMPc est limitant pour l’entrée matricielle de Ca2+ via l’uniport calcique mitochondrial (MCU) et, en conséquence, prévient la transition de perméabilité mitochondriale (MPT). En outre, dans les mitochondries isolées de cœurs de rats défaillants, la stimulation de la voie de l'AMPc par le HCO3- prévient la sensibilisation des mitochondries au Ca2+. Nous avons également constaté que les familles de phosphodiestérases (PDE), PDE2, 3 et 4, sont exprimées dans les mitochondries cardiaques régulant le taux d’AMPc. Ainsi, ces protéines forment une voie de signalisation locale dans la matrice régulant la fonction mitochondriale cardiaque. Finalement, notre étude a permis d’identifier un lien entre l'AMPc mitochondrial, le métabolisme, certaines PDEs et la mort cellulaire dans le cœur, qui est indépendant de la signalisation AMPc cytosolique. Ceci pourrait constituer un nouveau mécanisme cardioprotecteur via la préservation de la fonction mitochondriale dans un contexte physiopathologique. / CAMP is an important messenger in neurohormonal regulation of the heart. By activating its effectors, cAMP regulates many cellular functions such as gene expression, excitation-contraction coupling and cellular metabolism. In mammals, cAMP is produced by a family of adenylyl cyclase with various subcellular locations and membrane anchorage. The existence and role of cyclic nucleotide signaling in mitochondria has been postulated, but has not yet been demonstrated. Moreover, its implication in the regulation of cell death is still unknown. In this thesis, we demonstrated the local expression of several actors of cAMP signaling within cardiac mitochondria, namely a truncated form of soluble AC (sACt) and the exchange protein directly activated by cAMP 1 (Epac1) and showed a protective role for sACt against cell death, apoptosis as well as necrosis, in primary cardiomyocytes. Upon stimulation with bicarbonate (HCO3-) and Ca2+, sACt produces cAMP, which in turn stimulates oxygen consumption, increased the mitochondrial membrane potential (∆Ψm) and ATP production. cAMP is rate-limiting for matrix Ca2+ entry via the mitochondrial calcium uniporter (MCU) and, as a consequence, prevented mitochondrial permeability transition (MPT). In addition, in mitochondria isolated from failing rat hearts, stimulation of the mitochondrial cAMP pathway by HCO3- rescued the sensitization of mitochondria to Ca2+-induced MPT. We also found that PDE2, 3 and 4 families are located in cardiac mitochondria. They form a local signaling pathway with soluble AC in the matrix, which regulates cardiac mitochondrial functions. Thus, our study identifies a link between mitochondrial cAMP, mitochondrial metabolism, some PDEs and cell death in the heart, which is independent of cytosolic cAMP signaling. This might constitute a novel cardioprotective mechanism through mitochondrial function preservation in pathophysiological conditions.

Les Anthracyclines (ex : Doxorubicine (Dox)) fréquemment utilisées en chimiothérapie anticancéreuse peuvent conduire à une cardiotoxicité aboutissant à de l’insuffisance cardiaque et à une cardiomyopathie dilatée. Au niveau cellulaire, la Dox est connue pour générer un stress oxydant fort, s’intercaler directement entre les brins d’ADN, inhiber les Topoisomérase II (TopII) ou encore provoquer une détresse énergétique conduisant à la mort aussi bien des cellules tumorales que des cardiomyocytes. Néanmoins, les voies de signalisations/mécanismes moléculaires complets ne sont pas identifiés à ce jour. L’objectif de ce travail de thèse consiste donc à mieux comprendre les mécanismes de la cardiotoxicité de la Dox et à identifier de nouvelles cibles cellulaires cardio-protectrices limitant les effets cardiaques délétères de cette Anthracycline. Dans ce but, nous focalisons nos recherches sur le rôle de la protéine EPAC1, un facteur d’échange pour les petites protéines G directement activé par l’AMPc, dans la réponse des cellules cardiaques à la Dox. EPAC1 est une protéine centrale de la voie de signalisation AMPc dans le cardiomyocyte en réponse à une stimulation β-adrénergique. Or, plusieurs études ont récemment montré l’implication de certains acteurs de cette voie (Rac, RhoA) dans la cardiotoxicité induite par la Dox faisant d’EPAC1 une cible thérapeutique potentielle. Nous avons donc étudié in vitro (cultures primaires de cardiomyocytes de rat nouveau-nés (Dox 1µM)) et in vivo (souris sauvages ou invalidées pour EPAC1 (Dox, iv, 12mg/kg total)) les effets de la Dox sur l’expression et l’activité d’EPAC1 et sur les voies de signalisation qu’il régule. In vivo, les souris sauvages traitées à la Dox développent une cardiomyopathie dilatée associée à une altération de l’homéostasie calcique 15 semaines après traitement. In vitro, la Dox induit des modifications de l’expression/activité d’EPAC1 et de l’homéostasie calcique, la formation de complexes TopIIβ/ADN conduisant à des dommages à l’ADN, une dérégulation de la biogénèse et de l’activité de la chaîne respiratoire mitochondriale et finalement à l’apoptose des cardiomyocytes. L’inhibition pharmacologique (Ce3F4, Esi09) ou génétique d’EPAC1 réduit l’ensemble des dommages cellulaires in vitro et empêche le développement de la cardiomyopathie dilatée in vivo. De manière importante, nous montrons que contrairement à ce qui est observé dans les cellules cardiaques, l’inhibition d’EPAC1 augmente la toxicité de la Dox envers les cellules tumorales et en particulier envers les cellules MCF-7 issues de cancer mammaire métastatique, principale indication de la Dox. Nos résultats suggèrent donc que l’inhibition d’EPAC1 semble être une stratégie thérapeutique prometteuse dans la prévention de la cardiomyopathie induite par les traitements anticancéreux à base d’Anthracyclines. / Doxorubicin (Dox) is an Anthracycline commonly used to treat many types of cancer; unfortunately this chemotherapeutic agent often induces side effects such as cardiotoxicity leading to cardiomyocyte death and dilated cardiomyopathy (DCM). This cardiotoxicity has been related to reactive oxygen species generation, DNA intercalation, topoisomerase II inhibition and bioenergetics alterations resulting in DNA damages and ultimately in cardiomyocyte death. Nevertheless, complete molecular mechanisms are not yet identified. Therefore, there is a need for new treatment options and strategies aiming at reducing Dox side effects in the heart. Among these mechanisms, EPAC1 (Exchange Protein directly Activated by cAMP) signaling could be worth investigating as EPAC1 indirectly activates small G proteins (Rac1 and Rho A), which are known to be involved in Dox-induced cardiotoxicity. Therefore, we have investigated the effect of Dox on EPAC1 signaling in both in vivo mice model (C57BL/6 vs EPAC1 KO mice, iv injections, 12mg/kg) and in vitro model (primary culture of neonatal rat cardiomyocytes (NRVM), Dox 1μM). In vivo, Dox-treated mice developed a DCM associated with Ca2+ homeostasis dysfunction. In vitro, Dox induced DNA damages and cell death associated with huge mitochondrial disorders, characterized by a decrease in mitochondrial biogenesis and respiratory chain activity. This cell death is associated with apoptotic features including mitochondrial membrane permeabilization, caspase activation, cell size reduction and relative plasma membrane integrity. We also observed that Dox led to a modification of the protein level and the activity of EPAC1 in the same manner to the cAMP level. By contrast, the inhibition of EPAC1, prevented DNA/TopIIβ complexes, decreased Dox-induced DNA damages, loss of mitochondrial membrane potential, apoptosis and finally cardiomyocyte death. Mitochondrial biogenesis and respiratory chain activity operated normally when EPAC1 was inhibited. These results were confirmed in vivo since Dox-induced cardiotoxicity was prevented in EPAC1 KO mice as evidenced by unaltered cardiac function (no DCM) at 15 weeks post-treatment. Interestingly, the protection conferred by EPAC1 inhibition was not transferred in human cancer cell lines treated by Dox. Inhibition of EPAC1 could thus be a valuable therapeutic strategy to limit Dox-induced cardiomyopathy during cancer chemotherapy.

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No. of bitstreams: 1 arcarofilho_ca_dr_arafcf_int.pdf: 7378512 bytes, checksum: cb295c066a7be41be3508e2daf64d24f (MD5) Previous issue date: 2018-04-27 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Considerando os avanços no conhecimento acerca dos mecanismos que controlam o metabolismo de proteínas na musculatura esquelética que permitiram a busca por novas opções para o tratamento das atrofias musculares, o presente estudo teve como objetivo a compreensão do potencial antiproteolítico de inibidores de fosfodiesterase, PDE (pentoxifilina, inibidor não-seletivo de PDE; rolipram, inibidor seletivo de PDE4) em músculos esqueléticos de ratos submetidos à atrofia muscular devido à insuficiência insulínica (diabetes mellitus experimental), com ênfase na elucidação da participação de componentes da sinalização do AMP cíclico (AMPc) nesta resposta. Ratos normais e diabéticos (60 mg/kg de estreptozotocina, administração intravenosa) foram tratados com salina (NS e DS) ou com 2 mg/kg de rolipram (NROL e DROL), ou com 25 mg/kg de pentoxifilina (NPTX e DPTX) durante 3 dias, por via intraperitoneal. Após três dias de tratamento, músculos soleus e extensor digitorum longus (EDL) foram removidos, pesados, congelados e processados para diversas análises: (i) conteúdo de AMPc (ensaio imunoenzimático); (ii) atividades das proteases proteassoma, calpaínas e caspase-3 (uso de substratos específicos fluorigênicos); (iii) níveis proteicos e/ou níveis de fosforilação de componentes das vias proteolíticas, efetores intracelulares sinalizatórios e fatores de transcrição (Western blotting); (iv) determinação dos níveis séricos de insulina e citocinas pró-inflamatórias. Foram realizados experimentos ex-vivo, para verificar a ação direta dos fármacos no controle da proteólise muscular e ativação de efetores intracelulares, via incubações dos músculos na presença de rolipram ou de agonistas de EPAC (Exchange protein directly activated by cAMP) e de PKA (proteína quinase dependente de AMPc), proteínas efetoras ativadas pelo AMPc. Também foram realizados experimentos no Laboratório do Prof. Dr. Marco Sandri, no Venetian Institute of Molecular Medicine, Padova, Itália, para a avaliação do papel de PDE4D no controle do processo autofágico-lisossomal em músculos esqueléticos de camundongos jejuados. Os tratamentos de animais diabéticos com rolipram (DROL) ou com pentoxifilina (DPTX) promoveram uma redução nas atividades do proteassoma e calpaínas em soleus e EDL, bem como nos níveis de componentes-chave do sistema proteolítico ubiquitina-proteassoma (MuRF-1, atrogin-1, conjugados poliubiquitinados), e aumento nos níveis de calpastatina (inibidor das calpaínas). Interesante ressaltar que o grupo DROL apresentou redução na atividade e níveis proteicos de caspase-3, em ambos os músculos, enquanto que o grupo DPTX apenas em músculos EDL. Contribuindo com a redução observada na atividade de caspase-3, houve uma redução nos níveis de Bax (proteína pró-apoptótica) e aumento nos níveis de Bcl-2 (proteína anti-apoptótica) em ambos os músculos de animais DROL. Animais diabéticos tratados com salina (DS) apresentaram aumento nas atividades das três proteases, bem como nos níveis de componentes participantes destes processos proteolíticos. Animais normais e diabéticos tratados com salina (NS e DS) apresentaram níveis de AMPc basais e semelhantes entre si, tanto em soleus quanto em EDL, enquanto que os tratamentos de ratos normais e diabéticos com pentoxifilina (NPTX e DPTX) ou rolipram (NROL e DROL) promoveram aumentos de AMPc, em ambos os músculos. Um dos mecanismos que podem estar envolvidos na inibição da proteólise muscular após aumentos nas concentrações de AMPc envolve a proteína EPAC, responsável por integrar a sinalização do AMPc e a sinalização insulínica via ativação da quinase AKT. Animais diabéticos tratados com pentoxifilina ou com rolipram apresentaram aumento nos níveis proteicos de EPAC 1 e na fosforilação de AKT, quando comparados ao grupo DS. Observamos também um aumento na fosforilação inibitória de fatores de transcrição FoxO 1 e 3a em ambos os músculos de animais DROL. Podemos sugerir que parte das ações de rolipram que culminaram em ativação de AKT e inibição de FoxO na musculatura esquelética possam estar associadas aos aumentos observados nos níveis circulantes de insulina em animais DROL. Investigamos, apenas nos animais tratados com rolipram, a possibilidade de participação da proteína PKA no controle da proteólise muscular. Em animais DROL houve ativação da PKA, verificada tanto pelo aumento na fosforilação de substratos de PKA, bem como do fator de transcrição CREB, em soleus e EDL. Vale destacar que animais DS apresentaram níveis reduzidos de p-CREB e de substratos fosforilados por PKA em soleus e EDL. Animais diabéticos tratados com os inibidores de PDE apresentaram uma diminuição de citocinas pró-inflamatórias séricas (TNF-, PTX e ROL; IL-1, ROL) e aumento nos níveis de insulina sérica (ROL) em relação aos animais DS. Nos estudos ex vivo, as incubações de músculos soleus e EDL com rolipram levaram a uma redução da proteólise total, bem como aumento na fosforilação de substratos de PKA e de AKT. Músculos soleus e EDL incubados com agonistas de EPAC apresentaram aumento na fosforilação de AKT, enquanto que a incubação com agonista de PKA promoveu aumento na fosforilação dos substratos de PKA (em ambos os músculos) e aumento na fosforilação de AKT (apenas em EDL), quando comparados aos músculos incubados na ausência do fármaco. Nos estudos para compreensão do papel de PDE4D no controle do processo autofágico-lisossomal, observou-se que o silenciamento gênico da PDE4D em músculos tibialis anterior promoveu uma preservação da massa muscular e da área da fibra em animais jejuados, quando comparados ao músculo controle. Músculos flexor digitorium brevis, silenciados para PDE4D, apresentaram diminuição na expressão de proteínas-chave do processo autofágico-lisossomal, tais como LC3 e p62. Estes resultados evidenciam os mecanismos que podem estar envolvidos na ação direta de inibidores de PDE no controle do metabolismo proteico muscular esquelético, via ativação de duas vias dependentes de AMPc: (i) a via PKA/CREB, que pode participar do controle da transcrição de Bcl-2 e calpastatina, bem como na inativação direta de caspases, inibindo assim os processos proteolíticos dependentes de caspase-3 e calpaínas, (ii) a via EPAC/AKT, via fosforilação e inibição de FoxO 1 e 3A, regulando a expressão dos atrogenes (MuRF-1 e atrogin-1) e promovendo uma diminuição na atividade do sistema ubiquitina-proteassoma. Além disso, o tratamento com inibidores de PDE diminuem o processo inflamatório e aumentam os níveis circulantes de insulina, ações que podem contribuir para os efeitos antiproteolíticos. Evidências iniciais também sugerem que PDE4D participa no controle do sistema autofágico-lisossomal na musculatura esquelética. Todos estes resultados indicam que PDE participam no controle de processos proteolíticos, portanto inibidores de PDE emergem como uma opção interessante na ativação da sinalização do AMPc na musculatura esquelética, com vistas à utilização futura no tratamento de quadros de perda de massa muscular durante situações de atrofia. / Considering the advances in the knowledge of the mechanisms controlling the protein metabolism in skeletal muscles that allowed the discover of new options for the treatment of muscle atrophies, the present study aimed to understand the antiproteolytic potential of phosphodiesterase (PDE) inhibitors (pentoxifylline, a non-selective PDE inhibitor; rolipram, a selective PDE 4 inhibitor), in skeletal muscles of rats submitted to muscle atrophy due to insulin insufficiency (experimental diabetes mellitus), with emphasis on the elucidation of the participation of cyclic AMP (cAMP) signaling components. Normal and diabetic rats (60 mg/kg streptozotocin, intravenous administration) were treated intraperitoneally with saline (NS and DS) or with 2 mg/kg rolipram (NROL and DROL) or with 25 mg/kg pentoxifylline (NPTX and DPTX) for 3 days. After three days of treatments, soleus and extensor digitorum longus (EDL) muscles were removed, weighed, frozen and processed for several analyzes: (i) cAMP content; (ii) activities of proteasome, calpain and caspase-3 (use of specific fluorigenic substrates); (iii) protein levels and/or phosphorylation levels of components of proteolytic pathways, intracellular signaling effectors and transcription factors (Western blotting); (iv) determination of serum insulin and proinflammatory cytokines levels. Ex vivo experiments were performed to verify the direct action of the drugs in the control of muscle proteolysis and activation of intracellular effectors, via muscle incubations in the presence of rolipram or agonists of EPAC (Exchange protein directly activated by cAMP) and PKA (cAMP-dependent protein kinase), intracellular effectors activated by cAMP. Experiments were also carried out in the Laboratory of Prof. Dr. Marco Sandri at the Venetian Institute of Molecular Medicine, Padova, Italy, for the evaluation of the role of PDE4D in controlling the autophagic-lysosomal process in skeletal muscles of starved mice. Treatments of diabetic animals with rolipram (DROL) or pentoxifylline (DPTX) promoted a reduction in the activities of proteasome and calpain in soleus and EDL, as well as reduced the levels of key components of the ubiquitin-proteasome system (MuRF-1, atrogin-1, polyubiquitinated conjugates), and increased the levels of calpastatin (calpain inhibitor). Interestingly, DROL rats showed a reduction in the activity and in the protein levels of caspase-3 in both muscles, whereas DPTX rat had reductions only in EDL muscles. Contributing to the reduction in caspase-3 activity, it was observed a reduction in the content of Bax (pro-apoptotic protein) and an increase of Bcl-2 (anti-apoptotic protein) in both muscles of DROL rats. Diabetic animals treated with saline (DS) showed an increase in the activities of the three proteases, as well as increases in the levels of components belonging to these proteolytic processes. Normal and diabetic animals treated with saline (NS and DS) had basal and similar levels of cAMP in both soleus and EDL, whereas the treatments of normal and diabetic rats with pentoxifylline (NPTX and DPTX) or with rolipram (NROL and DROL) promoted increases in cAMP in both muscles. One of the mechanisms that may be involved in the muscle proteolysis inhibition after increases in cAMP involves the EPAC protein, responsible for integrating the cAMP and the insulin signaling pathways via AKT activation. Diabetic animals treated with pentoxifylline or with rolipram showed an increase in the protein levels of EPAC 1 and in the phosphorylation of AKT, when compared with the DS group. We also observed an increase in the phosphorylation (inhibitory) of FoxO 1 and 3a in both muscles of DROL rats. It can be suggested that part of the rolipram actions causing AKT activation and FoxO inhibition in skeletal muscles may be associated with the increases in the circulating levels of insulin observed in DROL animals. It was investigated, only in animals treated with rolipram, the possible involvement of PKA in the control of muscle proteolysis. DROL rats had activation of PKA, verified both by the increase in the phosphorylation of PKA substrates, as well as in the phophorylation of the transcription factor CREB, in soleus and EDL. DS rats had decreased levels of p-CREB and of the PKA substrates, in soleus and EDL. Diabetic animals treated with PDE inhibitors showed a decrease in serum proinflammatory cytokines (TNF-, PTX and ROL; IL-1, ROL) when compared with DS. In ex vivo studies, incubations of soleus and EDL with rolipram caused a reduction of the total proteolysis as well as an increase in the phosphorylation of PKA substrates and and of AKT. Soleus and EDL muscles incubated with EPAC agonist showed increased in the AKT phosphorylation, whereas incubation with PKA agonist promoted an increase in the phosphorylation of PKA substrates (in both muscles) and and increase in the AKT phosphorylation (EDL), when compared with muscles incubated in the absence of the drugs. In studies to understand the role of PDE4D in the control of the autophagic-lysosomal process, it was observed that the PDE4D gene silencing in anterior tibialis muscles caused a preservation of the muscle mass and fiber area in fasted animals when compared with control muscle. Flexor digitorium brevis muscles, silenced for PDE4D, showed a decreased expression of key proteins of the autophagic-lysosomal process, such as LC3 and p62. These results suggested the mechanisms that may be involved in the direct action of PDE inhibitors in the control of skeletal muscle protein metabolism, through activation of two cAMP-dependent pathways: (i) the PKA/CREB pathway, which may participate in transcriptional control of Bcl-2 and calpastatin, as well as causing direct inactivation of caspases, thus inhibiting the proteolytic processes dependent on caspase-3 and calpains, (ii) the EPAC/AKT pathway, via phosphorylation and inhibition of FoxO 1 and 3a factors, regulating the expression of atrogenes (MuRF-1 and atrogin-1) and promoting a decrease in activity of ubiquitin-proteasome system. Treatments with PDE inhibitors also decreased the inflammatory process and increased the circulating linsulin levels, which may be contributing to the antiproteolytic responses. Initial evidence also suggests that PDE4D participates in the control of the autophagy-lysosomal system in skeletal muscles. All these results indicate that PDE participate in the control of proteolytic processes, therefore PDE inhibitors emerge as an interesting option to activate the cAMP signaling in the skeletal muscles, which may be used in the future in treatments muscle mass loss during atrophy situations. / FAPESP: Processo 2013/18861-2 / FAPESP: Processo 2014/12202-0 / FAPESP: Processo 2017/02348-5

The soluble form of ADCYs, ADCY10, is ubiquitously expressed in the cytoplasm and distinct organelles including cell nucleus. In contrast to its membrane-associated isoforms (ADCY1-9) which are stimulated by G-protein-coupled receptors, ADCY10 is activated by bicarbonate (HCO3-) and can form cAMP in nearly all cell compartments. ADCY10 is involved in a variety of physiological as well as pathological processes including cell cycle control in tumor cells. However, the underlying mechanism is still unclear. Here the role of ADCY10 in cell cycle control and cell proliferation is studied in endothelial cells from human umbilical veins (HUVECs). The current study reveals that ADCY10 and α-Tubulin translocate and colocalize during mitosis suggesting a role of ADCY10 in cell division. In addition, FACS analysis demonstrated that ADCY10 plays a role in cell proliferation by modulating cell cycle control. Inhibition of ADCY10 by 0 mM HCO3- or 10 μM KH7 (specific ADCY10 inhibitor) induced cell accumulation in G2 phase rather than M phase determined by decreased mitotic indicator cyclin B1 level. Thus, ADCY10 inhibition leads to decreased cell proliferation. The known cAMP effectors, Epac and PKA, were assessed as possible downstream targets of ADCY10 in cell proliferation. It was shown that ADCY10 and Epac induce cell proliferation via ERK1/2-MAPK pathway. Inhibition of Epac was associated with suppressed cell proliferation. However, an arrest of cell cycle after Epac inhibition was observed in G0/G1 phases rather than S or G2/M phases. Thus, Epac inhibition causes a different arrest of cell cycle compared to ADCY10 inhibition. Regarding PKA, it was demonstrated that deficiency of PKA might play a role in either activation or inhibition of cell proliferation. However, direct inhibition of PKA by PKI and H-89 did not lead to cell accumulation in G2. This effect might be associated with broadened roles of PKA in different pathways. In contrast, direct stimulation of PKA under ADCY10 inhibition revealed that PKA is a downstream molecule of ADCY10 as a regulator of cell cycle transition from G2 to mitotic phase. However, the underlying pathway remains to be investigated. The cell cycle transition of G2/M phase is regulated by an auto-amplification loop of cyclin B1/CDK1, which is controlled by the kinase WEE1 and the phosphatase PP2A. WEE1 content was regulated via ADCY10 but was independent of PKA or Epac. Direct inhibition of PP2A showed a suppression of cell proliferation and induced cell cycle arrest in G2. These results were in accordance with those observed after the ADCY10. Furthermore, inhibition of ADCY10 had no effect on PP2A expression level but rather affected PP2A activity and was independent of Epac and PKA. Therefore, this data provides evidence that ADCY10 controls cell proliferation and cell cycle regulation via PP2A. Taken together, ADCY10 coordinates the cell cycle progression in a complex framework. Downstream of ADCY10, Epac promotes G1/S transition, whereas PKA mediates cell cycle transition of G2/M.

Inflammation or nerve injury sensitizes several populations of nociceptive neurons in the dorsal horn of the spinal cord, including those that express the neuropeptide Y (NPY) Y1 receptor (Y1R). Our overall hypothesis is that after tissue or nerve injury, these Y1R-expressing neurons enter a state of latent sensitization (LS) that contributes to vulnerability to the development of chronic pain; furthermore, LS is under the tonic inhibitory control of endogenous Y1R signaling. First, we evaluated the intracellular signaling pathways that become activated in Y1R-expressing neurons and participate in LS. To do this, we established behavioral models of inflammatory or neuropathic pain, allowed pain hypersensitivity to resolve, and then during this period of pain remission we administered the Y1R receptor antagonist, BIBO3304, by intrathecal injection. As observed previously with mu-opioid receptor antagonists/inverse agonists, we found that BIBO3304 reinstated pain hypersensitivity via an N-methyl-D-aspartate receptor (NMDAR)- and adenylyl cyclase type 1 (AC1)-dependent mechanism. Our subsequent behavioral pharmacological experiments then established two signaling pathways downstream of AC1 that maintain LS. The first pathway involves protein kinase A (PKA) and transient receptor potential cation channel A1 (TRPA1) and channel V1 (TRPV1). The second pathway involves exchange proteins activated by cAMP (Epac 1 and Epac 2). We next found that nerve injury decreases the co-expression of Y1R with markers of excitatory interneurons, suggesting that Y1R-expressing neurons acquire a pain-enhancing phenotype after peripheral nerve injury. In a separate set of experiments that utilized Y1R-receptor internalization as an index of NPY release, we found that nerve injury increased stimulus-evoked NPY release. We conclude that injury induces pain-facilitatory mechanisms of LS in the dorsal horn involving PKA→TRPA1 and PKA→TRPV1 at the central terminals of primary afferent neurons. Whether Epac mechanisms are located on these same presynaptic terminals and/or at Y1R-expressing excitatory interneurons remain to be determined. We also conclude that injury-induced LS is masked by a compensatory up-regulation of spinal NPY release that tonically inhibits pain. These results present a novel mechanism of injury-induced LS and endogenous control of the transition from acute to chronic pain by the NPY-Y1R system. Our work sheds light on novel targets for the treatment of chronic pain.

The ubiquitous second messenger cAMP acts to integrate and translate information encoded by extracellular messenger molecules, including hormones and neurotransmitters. Intracellular cAMP concentrations are regulated through coordinated changes in the activities of adenylyl cyclases (ACs) and cyclic nucleotide phosphodiesterases (PDEs). Freely diffusing cAMP can reach concentrations sufficient to activate cAMP effector proteins, such as protein kinase A (PKA) or the exchange protein activated by cAMP (EPAC), except in defined compartments where PDEs are localized which allows for spatial and temporal control of the cAMP signal. In human aortic vascular endothelial cells (HAECs) and HEK293T cells we recently identified a macromolecular complex consisting of PDE3B and EPAC and showed that this complex coordinated cAMP-induced effects on adhesion of these cells to fibronectin-coated surfaces. Using “pull-down” assays and peptide array-based approaches we have identified the molecular determinants which coordinate the formation of this complex. Our evidence suggests that the extreme N-terminal 13 amino acids of PDE3B represent the portion of PDE3B that interacts with EPAC. In addition, although several EPAC-encoded peptides were shown to bind PDE3B, immunoprecipitation-based studies identified a region proximal to the cAMP-binding domains as likely to have a dominant role in this binding. Of functional relevance, a cell permeable peptide containing these amino-terminal 13 amino acids of PDE3B antagonizes PDE3B-EPAC interactions in cells. In addition, this peptide impacted the ability of cAMP-elevating agents to coordinate EPAC-dependent cell adhesions. / Thesis (Master, Pathology & Molecular Medicine) -- Queen's University, 2009-10-06 19:07:12.01

yes / Pharmaceutical manipulation of cAMP levels exerts beneficial effects through the regulation of the exchange protein activated by cAMP (EPAC) and protein kinase A (PKA) signalling routes. Recent attention has turned to the specific regulation of EPAC isoforms (EPAC1 and EPAC2) as a more targeted approach to cAMP-based therapies. For example, EPAC2-selective agonists could promote insulin secretion from pancreatic β cells, whereas EPAC1-selective agonists may be useful in the treatment of vascular inflammation. By contrast, EPAC1 and EPAC2 antagonists could both be useful in the treatment of heart failure. Here we discuss whether the best way forward is to design EPAC-selective agonists or antagonists and the current strategies being used to develop isoform-selective, small-molecule regulators of EPAC1 and EPAC2 activity.

yes / Ca2+ release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. However, the signaling pathways that control this form of Ca2+ release are poorly understood and evidence of discrete Golgi Ca2+ release events is lacking. Here, we identified the Golgi apparatus as the source of prolonged Ca2+ release events that originate from the nuclear ‘poles’ of primary cardiac cells. Once initiated, Golgi Ca2+ release was unaffected by global depletion of sarcoplasmic reticulum Ca2+, and disruption of the Golgi apparatus abolished Golgi Ca2+ release without affecting sarcoplasmic reticulum function, suggesting functional and anatomical independence of Golgi and sarcoplasmic reticulum Ca2+ stores. Maximal activation of β1-adrenoceptors had only a small stimulating effect on Golgi Ca2+ release. However, inhibition of phosphodiesterase (PDE) 3 or 4, or downregulation of PDE 3 and 4 in heart failure markedly potentiated β1-adrenergic stimulation of Golgi Ca2+ release, consistent with compartmentalization of cAMP signaling within the Golgi apparatus microenvironment. β1-adrenergic stimulation of Golgi Ca2+ release involved activation of both Epac and PKA signaling pathways and CaMKII. Interventions that stimulated Golgi Ca2+ release induced trafficking of vascular growth factor receptor-1 (VEGFR-1) from the Golgi apparatus to the surface membrane. These data establish the Golgi apparatus as a juxtanuclear focal point for Ca2+ and β1-adrenergic signaling, which functions independently from the sarcoplasmic reticulum and the global Ca2+ transients that underlie the primary contractile function of the cell.

Cyclic nucleotides such as cAMP and cGMP serve as intracellular second messengers in diverse signaling pathways that control a wide range of cellular functions. Such pathways are regulated by key cyclic nucleotide receptor proteins including protein kinase A (PKA), the exchange protein directly activated by cAMP (EPAC), the hyperpolarization-activated cyclic-nucleotide-modulated (HCN) ion channels, and protein kinase G (PKG), and malfunction of these proteins has been linked to a number of pathologies. While it is known that cyclic nucleotide binding to these proteins leads to structural perturbations that promote their activation, the role played by dynamics in auto-inhibition and cyclic-nucleotide-dependent activation is not fully understood. Therefore, in this thesis we examined dynamics within the cyclic-nucleotide receptor proteins EPAC, HCN and PKG, and found that dynamics are critical for allosteric control of activation and/or autoinhibition of all three proteins. In particular, our findings for EPAC and HCN have highlighted dynamics as a key modulator of the entropic and enthalpic components, respectively, of the free-energy landscape for cAMP-dependent allostery, while our findings for PKG have highlighted dynamics as a key determinant of the cGMP-vs.-cAMP selectivity necessary to minimize cross-talk between signaling pathways. Ultimately, we envision that the methods outlined in this thesis will reveal key differences in the regulatory mechanisms of human cyclic nucleotide receptors that can eventually be exploited in the development of novel therapeutics to selectively target a single receptor, and thus treat physiological conditions/diseases linked to malfunction of the target receptor. / Thesis / Doctor of Philosophy (PhD) / In this thesis, we examined cyclic-nucleotide-responsive proteins that regulate key physiological processes, and whose malfunction has been linked to cardiovascular and neurological disorders. In particular, in three such proteins we examined dynamics, whose role in cyclic-nucleotide-responsive function is not fully understood. We found that cyclic-nucleotide-dependent variations in dynamics play a critical role in the function of these proteins, with the results for each protein highlighting a different role played by dynamics. Ultimately, we envision that the methods outlined in this thesis will reveal key functional differences among human cyclic-nucleotide-responsive proteins that can eventually lead to the development of novel therapeutics to treat certain diseases such as arrhythmias or epilepsy by selectively targeting a single cyclic-nucleotide-responsive protein.

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