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Contextualização - A distrofia muscular de cinturas tipo 2A ou calpainopatia é uma desordem causada pelas mutações no gene CAPN3 (15q15.1) que codifica a calpaína. Entender como ocorre a perda de força muscular, da mobilidade articular e suas relações com a função nestes pacientes pode auxiliar na melhor compreensão da evolução da doença e indicar os biomarcadores pertinentes para o acompanhamento desta doença. Objetivo - Descrever e correlacionar a força muscular, a amplitude de movimentos articulares (ADM) e a função de um grupo de pacientes brasileiros com distrofia muscular de cinturas tipo 2A (calpainopatia). Método - Trata-se de um estudo transversal. A população estudada foi composta por 50 pacientes acompanhados no Centro de Pesquisa sobre o Genoma Humano e Células Tronco (CEGH-CEL) do Instituto de Biociências da Universidade de São Paulo, São Paulo, Brasil. Foram coletados os dados de força muscular (Medical Research Council - MRC), amplitude de movimento, escala de Vignos, escala de Medida de Independência Funcional (MIF), teste de caminhada de 10 metros (TC10m) e Escala Egen Klassifikation (EK). Para análise de correlação entre a força muscular e função foram utilizados os testes de correlação de Pearson e de Spearman. Resultados - Houve correlação positiva forte entre o índice de força muscular de cotovelo e o escore da Escala de Medida de independência funcional total (MIFT) (rho=0.70) e correlação negativa forte entre a Escala de Vignos e escore da MIFT (rho= -0.90). No teste de caminhada de 10 metros, a média do tempo utilizado pelos participantes foi de 17.82 segundos. Os resultados mostraram correlação negativa moderada entre o escore da escala EK e o índice de força muscular (MRC) dos segmentos corporais do cotovelo (rho= -0.51) e punho (r= -0.40) para o subgrupo cadeirantes. A amplitude de movimento não é um biomarcador pertinente para o acompanhamento da doença, pois não apresentou correlação com as demais variáveis deste estudo. A maioria dos pacientes apresentou limitações articulares na região de joelho e tornozelo, condizentes com outras pesquisas. A comparação da força muscular entre os músculos extensores dos joelhos direito e esquerdo mostrou diferença significativa (p < 0.02). Conclusão - Amostra brasileira apresentou incidência similar com os países do continente europeu (32%). Os escores de força muscular mostraram correlação com a função motora. Nossos achados permitem determinar, com melhor embasamento, os biomarcadores funcionais força muscular e função como os mais indicados na prática clínica e de pesquisa / Contextualization - Limb-girdle muscular dystrophy type 2A or calpainopathy is a disorder caused by mutation in the CAPN3 gene (15q15.1) that codes for calpain. Understanding how loss of muscular strength, joint mobility and their relationship with the function in these patients can help in better understanding the evolution of the disease and indicate the biomarkers pertinent to the follow-up of this disease. Objective - To describe and correlate muscle strength, range of joint movements (ROM) and function of a group of Brazilian patients with limb-girdle muscular dystrophy type 2A (calpainopathy). Method - This is a cross-sectional study. The studied population was composed for 50 patients at the Center for the Study of the Human Genome (CSHG) of the Institute of Biosciences of the University of São Paulo, São Paulo, Brazil. The data recorded were muscle strength (Medical Research Council - MRC), range of motion, Vignos scale, Functional Independence Measure (FIM), 10-meter walk test and Egen Klassifikation scale (EK). Para análise de correlação entre a força muscular e função foram utilizados os testes de correlação de Pearson e de Spearman. Results - There was a strong positive correlation between MRC and FIM (rho=0.70) and negative correlation between the Vignos Scale and FIM (rho= -0.90). The 10-meter walk test, the mean time used by participants was 17.82 seconds. The results showed a moderate negative correlation between the EK scale score and the MRC of the elbow (rho = -0.51) and wrist (r = -0.40) for the wheelchair subgroup. The range of motion is not a biomarker pertinent to the disease follow-up, since it did not present a correlation with the other variables of this study. The patients had contractures around the knee and ankle, is in keeping with what other studies. The comparison of muscle strength between the extensor muscles of the right and left knees showed a significant difference (p < 0.02). Conclusion - Brazilian sample had an incidence similar with the countries of the European continent (32%). The scores of muscle strength and motor function showed correlation. Our findings allow us to determine, with better foundation, functional biomarkers muscle strength and function as the most indicated in clinical practice and research

La spasticité et la douleur neuropathique sont deux symptômes apparaissant fréquemment après une lésion médullaire. La spasticité est définie comme une augmentation du tonus musculaire qui provoque des contractures, tandis que la douleur neuropathique se caractérise par des sensations douloureuses survenant suite à une lésion du système nerveux.Ces deux symptômes résultent en partie d’une désinhibition des réseaux neuronaux sous-lésionnels lié à une diminution de l’expression du cotransporteur potassium-chlorure type 2 (KCC2). Pour être efficace,l’inhibition nécessite l’action de cette protéine qui extrait les ions chlorure des neurones.L’objectif de la présente thèse est donc d’identifier des médicaments capables d’activer KCC2 afin de restaurer l’inhibition dans le but de traiter la spasticité et la douleur neuropathique.Dans un premier temps, nos résultats ont montré que l’activation de récepteurs sérotoninergiques 5-HT2A avec le TCB-2 rétablit l’expression de KCC2 dans la corne dorsale après une lésion médullaire ou névrectomie. Or le TCB-2 réduit seulement la douleur neuropathique après la lésion spinale.Par la suite, nous avons identifié la prochlorperazine comme une molécule augmentant l’activité de KCC2. Si la prochlorperazine est efficace contre la spasticité, elle a néanmoins un effet plus modeste envers l’allodynie mécanique suite à une lésion médullaire.Enfin, nous avons démontré que la diminution de KCC2,ainsi que l’hyperexcitabilité des motoneurones suite à la lésion, dépendent de l’activation des calpaïnes.Cette thèse valide KCC2 comme une cible thérapeutique dans le traitement de la spasticité et la douleur neuropathique suite à une lésion médullaire. / Spasticity and neuropathic pain are two symptoms that arise frequently after a spinal cord injury. Spasticity is defined as an increase of the muscle tone contributing to cramps, whereas neuropathic pain consists of painful responses caused by a damaged nervous system. Both symptoms arise, in part, due to a loss of inhibition in the sublesional neural networks, linked to a downregulation of the expression of potassium-chloride cotransporter type 2 (KCC2). For inhibition to be efficient, the action of this protein, which extrudes chloride ions from neurons, is needed.The objective of this thesis is, therefore, to identify drugs capable of activating KCC2 to recover inhibition with the objective of treating spasticity and neuropathic pain.First, our results have proven that the activation of serotonin receptors 5-HT2A with TCB-2 restores KCC2 expression in the dorsal horn after a spinal cord or peripheral nerve injury. However, TCB-2 reduces neuropathic pain after a spinal cord injury exclusively.In the next stage of the work, we have identified prochlorperazine as an enhancer of KCC2 activity. Prochlorperazine is efficient against spasticity, although it only showed a modest reduction of mechanical hyperalgesia in animals with a spinal cord injury.Lastly, we have proven that KCC2 downregulation and motoneuron hyperexcitability after a spinal cord injury depend on the overactivation of calpains.This thesis validates KCC2 as a druggable target to treat spasticity and neuropathic pain after spinal cord injury.

<p>Historically, the meat industry has struggled to provide consumers with consistent beef tenderness. Various post-harvest technologies have been used in industry; however, there is still a need to develop a natural and safe post-harvest processing system that can be used to create consistently tender products for consumers. In addition to postmortem aging being a time-consuming process, literature has suggested that it is not a sufficient method to achieve tenderization in certain cull cow muscles. This has resulted in the large supply of cull cow beef to be underutilized due to its inferior quality, specifically tenderness. Applying a combination of mechanical tenderization with additional postmortem aging may be an effective strategy to overcome deficiencies in beef tenderness. Recent studies have found that tumbling without brine addition can be successful at improving instrumental tenderness and consumer liking of tenderness of fresh beef loin. The physical disruptions of muscles, which likely occur during tumbling, may enhance activity of proteolytic enzymes and thus induce more tenderization. The overall objective of this thesis was to investigate the effects of fresh beef tumbling methods and postmortem aging times on the tenderness and proteolysis of loin muscles from both A maturity cattle and cull cows.</p> <p>The first chapter of this thesis is a literature review that will address the factors affecting tenderness and the methods used by the industry to improve tenderness, specifically focusing on meat tumbling and cull cow beef. The second chapter is a study that investigated the effects of fresh beef tumbling at different postmortem times on meat quality attributes and proteolytic features of loins. The results from this study suggest that early postmortem tumbling coupled with aging can synergistically impact the improvements of beef loin tenderness and proteolysis, shortening the necessary aging period. The third and final chapter of this thesis is a study that aimed to determine the effect of fresh beef tumbling and postmortem aging on the quality and proteolysis of loins from cull cows. The results from this study indicate that aging would be effective at improving the quality and palatability of cull cow beef loins, although tumbling could improve consumer liking of tenderness at earlier postmortem times.</p>

Enterohemorrhagic E. coli (EHEC) is a major cause of food borne diarrheal illness worldwide. While disease symptoms are usually self-resolving and limited to severe gastroenteritis with bloody diarrhea, EHEC infection can lead to a life threatening complication known as Hemolytic Uremic Syndrome (HUS), which strikes children disproportionately and is the leading cause of kidney failure in children. Upon infection of gut epithelia, EHEC produces characteristic lesions called actin pedestals. These striking formations involve dramatic rearrangement of host cytoskeletal proteins. EHEC hijacks mammalian signaling pathways to cause destruction of microvilli and rebuilds the actin cytoskeleton underneath sites of bacterial attachment. Here, we present a brief study on a host factor, Calpain, involved in microvilli effacement, and an in depth investigation on a bacterial factor, EspFU, required for actin pedestal formation in intestinal cell models. Calpain is activated by both EHEC and the related pathogen, enteropathogenic E. coli (EPEC), during infection and facilitates microvilli disassembly by cleavage of a key membrane-cytoskeleton anchoring substrate, Ezrin. Actin pedestal formation is facilitated by the injection of two bacterial effectors, Tir and EspFU, into host cells, which work in concert to manipulate the host actin nucleators N-WASP and Arp2/3. EspFU hijacks key host signaling proteins N-WASP and IRTKS by mimetic displacement and has evolved to outcompete mammalian host ligands. Multiple repeats of key functional domains of EspFU are essential for actin pedestal activity through proper localization and competition against the an abundant host factor Eps8 for binding to IRTKS.

The mechanism of microparticle shedding from the plasma membrane of calcium-loaded cells has been investigated in erythrocytes and platelets. Recent studies have revealed the physiological and clinical importance of microparticle release from nucleated cells such as lymphocytes and endothelium. The experiments of this study were designed to address whether simple mechanisms discovered in platelets and erythrocytes also apply to the more complex nucleated cells. Four such mechanisms were addressed: potassium efflux, transbilayer phosphatidylserine migration, cytoskeleton degradation, and membrane lipid order. The rate and amount of microparticle release in the presence of a calcium ionophore, ionomycin, was assayed by light scatter at 500 nm. To inhibit the calcium-activated potassium current, cells were exposed to 1 mM quinine or a high-potassium buffer. Both interventions substantially attenuated microparticle shedding induced by ionomycin. Microparticle release was also greatly reduced in a lymphocyte cell line deficient in the expression of scramblase, the enzyme responsible for calcium-stimulated phosphatidylserine migration to the cell surface. This result indicated that such phosphatidylserine exposure is also required for microparticle shedding. The importance of cytoskeletal rearrangement was evaluated through the use of E64-d, a calpain inhibitor, which appeared to have no affect on release. Thus, if cytoskeleton degradation is important for microparticle release, a different enzyme or protein must be involved. Finally, the effect of membrane physical properties was addressed by varying the experimental temperature (32–42 °C). A significant positive trend in the rate of microparticle release as a function of temperature was observed. Fluorescence experiments with trimethylammoniumdiphenylhexatriene and patman revealed significant differences in the level of apparent membrane order along that temperature range. Ionomycin treatment appeared to cause further disordering of the membrane, although the magnitude of this change was minimally temperature-sensitive. Thus, it was concluded that microparticle release depends more on the initial level of membrane order than on the change imposed by calcium uptake. In general, mechanisms involved in particle release from platelets and erythrocytes appeared relevant tolymphocytes with the exception of the hydrolytic enzyme involved in cytoskeletal degradation.

The lens of the eye needs to be completely transparent in order to allow all light entering the eye to reach the retina. This transparency is maintained by the highly ordered structure of the lens proteins the crystallins. Any disruption to the lens proteins can cause an opacity to develop which is known as cataract. During cortical cataract formation there is increased truncation of the lens crystallins. It is believed that overactivation of calcium-dependent cysteine proteases, the calpains, is responsible for the increased proteolysis of the crystallins seen during cataractogenesis. Within the ovine lens there are three calpains, calpain 1, 2 and the lens specific calpain Lp82. The aim of this thesis was to determine the changes in the lens proteins during ageing and cataractogenesis, and to establish the role of the calpains in these processes. Calpain 1 and 2 were purified from ovine lung and Lp82 was purified from lamb lenses using chromatography. Activity and presence of the calpains was determined by using the BODIPY-FL casein assay, gel electrophoresis, Western blot and casein zymography. Changes in the lens proteins, specifically the crystallins, were visualised using two-dimensional electrophoresis (2DE). Lenses from fetal, 6 month old and 8 year old sheep were collected, as well as stage 0, 1, 3 and 6 cataractous ovine lenses. The proteins from the lenses were separated into the water soluble and urea soluble fractions and analysed by 2DE. Mass spectrometry was used to determine the masses and therefore modifications of the crystallins. Finally, the individual crystallins were separated using gel filtration chromatography and incubated with the purified calpains in the presence of calcium. The extent of the proteolysis was visualised using 2DE and truncation sites determined by mass spectrometry. Purification of the calpains resulted in samples that were specific for each calpain and could be used in further experiments. 2DE analysis showed that there were changes to the crystallins during maturation of the lens. The α-crystallins become increasingly phosphorylated as the lens ages and a small amount becomes truncated. The β-crystallins were also modified during ageing by truncation and deamidation. When crystallins from cataractous lenses were compared using 2DE there were changes to both the α- and β-crystallins. The α-crystallins were found to be extensively truncated at their C-terminal tail. Four of the seven β-crystallins, βB1, βB3, βB2 and βA3, showed increased truncation of their N-terminal extensions during cataract formation. All three calpains truncated αA and αB-crystallin at their C-terminal ends after incubation. Calpain 2 and Lp82 each produced unique αA-crystallin truncations. All three calpains truncated βB1 and βA3 and calpain 2 also truncated βB3. When the truncations from the calpain incubations were compared to those seen during cataract formation, many of the truncations were found to be similar. Both the unique truncations from calpain 2 and Lp82 were found in cataractous lenses, with the Lp82 more obvious in the 2DE. The β-crystallin truncations found after incubation with the calpains were similar to those found during cataractogenesis. In conclusion this study documents the changes to the ovine lens during maturation and cataractogenesis and indicates a role for the calpain family in the increased proteolysis observed in the ovine cataract.

Chapter 1 gives background information on proteases and discusses the concept of protease inhibition as a therapeutic strategy for humans. It introduces the key concept that conformation defines biological activity. It also outlines how proteases almost universally bind their substrate/inhibitors in an extended β-strand conformation. The use of calpain as a prototype protease for the testing of β-strand mimics synthesised later in the thesis is also discussed. Chapter 2 describes how molecular modeling was used to rationalise the structure based activity relationships (SAR) of known calpain inhibitors. Molecular modeling was then used to successfully design a number of acyclic β-strand mimics. The synthesis and testing of eight such inhibitors is described. The most potent β-strand mimic prepared was 2.13. This was determined to have an IC₅₀ of 30 nM against calpain II. Chapter 3 outlines the history and application of ring closing metathesis (RCM) to the synthesis of cyclic compounds. The attempted synthesis of an eight membered cyclic nitrogen to nitrogen conformationally constrained dipeptide is described. The synthesis of a conformationally constrained β-amino acid calpain inhibitor (3.73) is also described. A novel calpain inhibitor motif was designed in Chapter 4. On the basis of this an in-silico combinatorial library of two hundred and eighty eight possible β-strand templates was prepared. Conformational analysis of this library was performed and from this a number of excellent β-strand templates were identified and selected for synthesis. The preparation of ten β-strand templates is described. New microwave irradiation methodology was developed to achieve this. vii The formation of a six-membered catalyst deactivating chelate is also proposed to explain why some dienes fail to undergo RCM. Two methods to circumvent the formation of such a chelate are outlined. The addition of Lewis acid chloro-dicyclohexyl borane to the RCM reaction mixture and chain length alteration are investigated. Chapter 5 describes the design of macrocyclic β-strand mimics using induced fit molecular modelling. The physicochemical properties of these were calculated in-silico. From this analysis a number of Tyr-XX-Gly based and Tyr-XX-Cys based macrocyclic calpain inhibitors were selected for synthesis. The preparation and testing of these are described. In the Tyr-XX-Gly macrocyclic system a number of variables were investigated and numerous SAR implications concluded. Aldehyde 5.14 was identified as the best electrophilic warhead macrocyclic calpain inhibitor with an IC₅₀ against calpain II of 27 nM. The best non-electrophilic warhead macrocycle (5.13) had an IC₅₀ against calpain II of 704 nM. Chapter 6 describes synthetic optimisation for the preparation of calpain inhibitors 2.13, 5.14 and 5.17. Multi-gram quantities of each were prepared. Aldehydes 2.13 and 5.14 were evaluated as anti-cataract agents using in-vivo cataract sheep model. Both of these β-strand mimics were demonstrated to retard cataract development. Macrocycle 5.14 was found to be the most effective, decreasing the rate of cataract development between forty four and forty nine per cent relative to control. Chapter 7 outlines the attempted development of RCM methodology for the chiral synthesis of α-α disubstituted amino acid lactams. In addition, methodology for the stereoselective incorporation of a C-N constrained β-amino acid carbocycle into a peptide or peptidomimetic is described.

Introdução: As distrofias musculares de cinturas (limb-girdle muscular dystrophies - LGMD) são causadas por mutações em uma grande variedade de genes que codificam proteínas musculares, podendo ser herdadas de forma autossômica dominante ou recessiva. O diagnóstico é feito tanto através de exame de biópsia muscular que mostra um padrão histológico distrófico ao lado de deficiência específica de proteínas musculares quanto por estudo genético. Em alguns subtipos de LGMD não é possível fazer o diagnóstico específico pela biópsia muscular, tais como na deficiência da calpaína-3 (CAPN3) e da proteína relacionada a fukutina (FKRP). Nestes casos, portanto, o exame molecular é de grande valor para a confirmação do diagnóstico. Objetivos: Analisar os genes CAPN3 e FKRP em pacientes com diagnóstico histológico de LGMD e verificar a expressão proteica da CAPN3 nesses pacientes, correlacionando com as mutações identificadas e com o quadro clínico e histológico dos mesmos. Resultados: Fizeram parte deste estudo 36 pacientes com LGMD provenientes do ambulatório de miopatias do HC-FMUSP em que a biópsia muscular não identificou deficiência de distrofina, disferlina, caveolina-3 e sarcoglicanas. Destes, nove (25%) foram diagnosticados com LGMD2A, seis (17%) com LGMD2I e em 21 (58%) não foi possível identificar o subtipo específico. Foram encontradas mutações patogênicas no gene CAPN3 em oito pacientes, sendo em homozigose em dois casos, heterozigose composta em cinco casos e em heterozigose em um caso. Em um caso o diagnóstico de LGMD2A foi realizado baseado apenas na análise da expressão da proteína CAPN3 no tecido muscular. Em seis pacientes foram identificadas mutações patogênicas no FKRP, sendo em homozigose em cinco casos e em heterozigose em um caso. A maioria dos pacientes com LGMD2I (cinco casos) apresentava a mutação c.826C > A. Foi observada ausência total ou parcial da expressão da CAPN3 em pacientes com LGMD2A. Conclusões: O presente estudo mostrou que mutações nos genes CAPN3 e FKRP são frequentes em pacientes com diagnóstico clínico e histológico de LGMD. A análise da expressão da CAPN3 se mostrou como uma importante ferramenta no diagnóstico da LGMD2A / Introduction: The Limb-Girdle Muscular Dystrophies (LGMD) are caused by mutations on a wide variety of genes that encode muscular proteins which can be inherited in dominant or recessive autosomal forms. The diagnosis is made either by genetic study or by muscle biopsy which shows a dystrophic histologic pattern with specific deficiency of muscular proteins. On some LGMD subtypes such as calpain-3 (CAPN3) and fukutin related protein (FKRP) deficiencies it is not possible to make a specific diagnosis by muscle biopsy. In these cases, the molecular exam is of great value to confirm the diagnosis. Objectives: Analyze the CAPN3 and FKRP genes in patients with histological diagnoses of LGMD, and verify the protein expression of CAPN3 on these patients correlating it with the identified mutations and their clinical and histological pattern. Results: Thirty-six patients with LGMD, where the muscular biopsy did not identify deficiency of dystrophin, dysferlin, caveolin-3 and sarcoglycans, from the Muscle Ambulatory of HC-FMUSP took part in this study. Of these, nine (25%) were diagnosed with LGMD2A, six (17%) with LGMD2I, and on 21 of them (58%), it was not possible to identify the specific subtype. Pathogenic mutations on CAPN3 were found in eight patients, being homozygous in two cases, compound heterozygous in five cases and heterozygous in one case. The diagnosis of LGMD2A in one patient was done based exclusively by CAPN3 protein analysis on the muscle tissue. Pathogenic mutations on FKRP were found in six patients, being homozygous in five cases and heterozygous in one case. Most of the patients with LGMD2I (five cases) presented the mutation c.826C > A. It was observed total or partial absence of the CAPN3 expression in patients with LGMD2A. Conclusions: The study showed that mutations on CAPN3 and FKRP are frequent in patients with clinical and histological diagnosis of LGMD. The CAPN3 expression analysis proved as an important tool in the LGMD2A diagnosis

O complexo distrofina-glicoproteínas associadas (DGC) localiza-se no sarcolema das células musculares esqueléticas e cardíacas e tem como função principal proporcionar ligação mecânica entre o citoesqueleto intracelular e a matriz extracelular. Estudos prévios realizados em nosso laboratório, focalizando o complexo DGC, demonstraram perda de proteínas importantes desse complexo. As situações avaliadas anteriormente foram: infecção experimental por Trypanosoma cruzi (T. cruzi) e sépsis experimental. Em ambas as situações verificou-se a perda da distrofina acompanhada por disfunção contrátil e aumento nos níveis da calpaína, protease dependente de cálcio implicada na proteólise da distrofina. Todavia, o mecanismo responsável pela ativação das calpaínas e proteólise da distrofina na infecção experimental por T. cruzi e na sépsis experimental não está totalmente definido. O objetivo desse trabalho foi avaliar in vitro o mecanismo responsável pela ativação das calpaínas nas culturas de cardiomiócitos desafiadas com o soro dos animais infectados experimentalmente com T. cruzi ou com o soro dos animais submetidos à sépsis grave experimental. Camundongos C57BL/6 foram submetidos à sépsis grave ou infectados com a cepa Y de T. cruzi. No pico de expressão das citocinas pró-inflamatórias, 12 dias após inoculação do parasito ou 6 horas após a indução da sépsis, o sangue foi coletado e o soro separado. Corações de camundongos recém-nascidos foram isolados para o cultivo dos cardiomiócitos. No quinto dia após o início das culturas, as células foram estimuladas com 10% do soro de animais infectados com T. cruzi ou o soro de animais submetidos à sépsis grave durante 24 horas. Após, as células foram coletadas para análises de Western blotting e imunofluorescência para verificar a expressão da distrofina e calpaína-1. Avaliou-se também, por imunofluorescência, a expressão do NF-B. Os cardiomiócitos foram estimulados e tratados com o dantrolene, inibidor da liberação de cálcio do retículo sarcoplasmático, ou ALLN, inibidor da calpaína-1, e após coletados para verificar a expressão da distrofina e calpaína-1 por Western blotting e imunofluorescência. Nossos resultados mostraram uma redução significativa na expressão da distrofina com desarranjo das miofibrilas contráteis e formação de bolhas citoplasmáticas, além de um aumento nos níveis da calpaína-1 e do NF-B. O tratamento com dantrolene nas culturas estimuladas com o soro de animais infectados experimentalmente com T. cruzi ou com o soro dos animais submetidos à sépsis grave, recuperou a expressão da distrofina e reduziu os níveis da calpaína-1. O tratamento com ALLN nos cardiomiócitos estimulados com o soro de animais infectados experimentalmente com T. cruzi recuperou a expressão da distrofina e não alterou os níveis da calpaína-1. Nas culturas estimuladas com o soro dos animais submetidos à sépsis grave, o tratamento com o ALLN recuperou a expressão da distrofina e reduziu os níveis da calpaína-1. Nossos resultados demonstraram que citocinas pró-inflamatórias presentes no soro dos animais infectados experimentalmente com T. cruzi como também no soro dos animais submetidos à sépsis grave induziriam um aumento no influxo de cálcio com consequente ativação das calpaínas, as quais atuariam na ativação do NF-B e na degradação da distrofina. Esse mecanismo poderia ser responsável pela proteólise da distrofina cardíaca observada na infecção experimental por Trypanosoma cruzi como também sépsis experimental. Mais estudos são necessários para elucidar este mecanismo, principalmente em relação a inibidores dos canais de cálcio, das citocinas pró-inflamatórias e das calpaínas, com o objetivo de fornecer novas vias de intervenção na prevenção de alterações cardíacas observadas na doença de Chagas e na sépsis. / The dystrophin-glycoprotein complex (DGC), located in the sarcolemma of cardiac and skeletal muscle cells and concentrated along the plasma membrane in costameric structures provides a framework that connects the intracellular cytoskeleton to the extracellular matrix. Previous studies from our laboratory clearly demonstrated disruption of DGC proteins in experimentally-induced T. cruzi infection and experimental sepsis. Both situation presented dystrophin disruption associated with contractile dysfunction and increased calpain levels, calcium dependent protease responsible for dystrophin proteolysis. However, the mechanism responsible for calpain activation and dystrophin proteolysis in experimentally-induced T. cruzi infection and experimental sepsis is not totally understood. The aim of this study was to evaluate in vitro the mechanism responsible for calpain activation in cultured cardiomyocytes challenged with serum from animals experimentally infected with T. cruzi or subjected to severe sepsis. Mice C57BL/6 were subjected to sepsis induction or infected with Y strain from T. cruzi. At the peak of proinflammatory cytokines expression, 12 days after parasite inoculation or 6 hours after sepsis induction, the blood was collected and the serum separated. Hearts from newborn mice were isolated for culture of cardiomyocytes. After 5 days of incubation, the cardiac cells were stimulated with 10% of serum from animals experimentally infected with T. cruzi or subjected to severe sepsis during 24 hours, and collected for Western blotting and immunofluorescence analysis to verify dystrophin and calpain-1 expression. The expression of NF-B was evaluated by immunofluorescence. The treatments with dantrolene, inhibitor of calcium release from sarcoplasmic reticulum, or ALLN, calpain-1 inhibitor, were performed in cultured cardiomyocytes stimulated during 24 hours with serum from animals infected with T. cruzi or subjected to severe sepsis, and dystrophin and calpain-1 expression were analyzed by Western blotting and immunofluorescence. Our results demonstrated loss of dystrophin associated with myofibers derangement and presence of cytoplasmic blebs as well increase of calpain-1 and NF-B expression. The dantrolene treatment in cultures stimulated with serum from animals infected with T. cruzi or subjected to severe sepsis recovey dystrophin expression and reduced calpain-1 levels. The ALLN treatment in cardiomyocytes stimulated with serum from animals infected with T. cruzi recovery dystrophin expression and preserved calpain-1 levels. In cultures stimulated with serum from animals subjected to severe sepsis, the ALLN treatment recovery dystrophin expression and decreased calpain-1 levels. Our results demonstrated that proinflammatory cytokines in serum from mice infected with T. cruzi or subjected to severe sepsis could induce an increase calcium influx with calpain activation, which could act in NF-B activation and dystrophin disruption. Possibly, this mechanism could be responsible to dystrophin proteolysis observed in experimentally-induced acute T. cruzi infection and experimental sepsis. More studies are needed to elucidate this mechanism, especially in relation to calcium channel blockers and inhibitors of pro-inflammatory cytokines and calpains, which may provide new routes for intervention to prevent cardiac damage in Chagas disease and sepsis.