Hamm et al., 2021 reported that voluntary wheel running (R) was complementary to micro-dystrophin gene therapy (GT) in mdx mice, a model of Duchenne muscular dystrophy (DMD). After 21 weeks of running, time to fatigue on a treadmill for the mdxRGT mice was increased 1.8-fold compared to mdxGT mice (no run) and ~5-fold compared to mdx mice (no micro-dystrophin, no run). Fatigue times for mdxRGT were similar to wild type runners (WTR), while mdxGT and WT (no run) were also similar. The diaphragm is an important muscle for endurance exercise. Remarkably, diaphragm power in mdxRGT was depressed compared to mdxGT, suggesting a negative impact of running on GT. To explore mechanisms to explain this decrease, transcriptome profiles for each of the study groups were assessed. RNASeq data revealed differentially expressed genes (DEGs) from groupwise comparisons. Transcripts identified using the Jackson Labs' Gene Expression Database and extensive literature review were organized into a master signaling pathway composed of two sub-pathways: muscle regeneration and fast-slow fiber type shift. Both sub-pathways were hypothesized to explain the improved treadmill performance despite decreased diaphragm power in mdxRGT as potential adaptive mechanisms. Analysis revealed that GT alone (mdxGT) rescued transcriptome expression to WT values in the mdx phenotype more than GT and running combined (mdxRGT). This outcome indicates that, at the 26-week timepoint of sacrifice, the signaling of the transcripts in the muscle regeneration and fast-slow fiber type shift sub-pathways was likely not responsible for the observed improved running performance of mdxRGT compared to mdx. / Master of Science / Muscular dystrophy is a group of diseases characterized by progressive muscle wasting and loss of function. Duchenne muscular dystrophy (DMD) is the most common of these conditions, with an occurrence of 18 per 100,000 live births. The muscles of people with DMD lack a protein called dystrophin, which provides structural integrity for muscle fibers during contraction. This lack of dystrophin leads to muscle deterioration over time, leading to people with DMD typically being wheelchair-bound by ten years of age. Animal models of DMD have been created over time to help study this condition. One such model, the mdx mouse, was used in the study that led to this thesis project. In this study, Hamm et al., 2021, some of these mdx mice were given a micro-dystrophin gene therapy (GT). This GT aimed to deliver a smaller, but still functional version of the missing dystrophin protein to the mice, which has been shown to be beneficial in other studies. This study aimed to measure the effect of this GT when combined with voluntary wheel running. As people with DMD cannot exercise under current clinical guidelines, measuring the response of mdx mice to GT and running combined is an important step in determining the safety of such a treatment in human patients. In the study conducted by Hamm et al., 2021, the mice that received the micro-dystrophin GT and access to running wheels (mdxRGT) performed almost twice as well on a treadmill running test than the mice that received GT alone (mdxGT). Despite this positive result, the mdxRGT mice showed decreased diaphragm power generation compared to mdxGT mice. As the diaphragm is the most important breathing muscle, it is also very important for running performance; therefore, the decreased diaphragm power generation seen in mdxRGT mice is apparently contrary to their improved running performance. To explain this discrepancy, this thesis project examined the diaphragm transcriptome of the different groups in Hamm et al., 2021. The transcriptome is the sum total of messenger ribonucleic acid (mRNA) expressed in a given tissue. Deoxyribonucleic acid, or DNA, is transcribed into mRNA, which is then translated into protein. As such, this thesis project looked at the mRNA expressed in the diaphragm of the mice in the various groups of Hamm et al., 2021, specifically comparing the mdxGT and mdxRGT groups. Important mRNA transcripts, or genes, were identified and assembled into signaling pathways, cascades that highlight how transcripts affect each other and ultimately lead to function once they are translated into their corresponding proteins. Two such signaling pathways were generated based on mechanisms that were thought to contribute to the improved running performance-decreased diaphragm power discrepancy in mdxRGT mice -slow fiber type shifting, and muscle fiber regeneration. The expression of many of the mRNA transcripts in these resulting pathways was closer to the control group in mdxGT compared to mdxRGT. The control group was made up of healthy mice, and as such, their transcript expression level is seen as normal. This outcome of mdxGT having more similar expression to the control group than mdxRGT suggests that the expression of the transcripts included in the two signaling pathways (fast-slow fiber type shift and muscle fiber regeneration) likely did not explain the improved running performance despite decreased diaphragm power in mdxRGT mice. As such, future studies are warranted.

The intrinsic laryngeal muscles are recognized as a highly specialized allotype of skeletal muscle. To date, much of the research examining the properties of this muscle group has been conducted on 2 primary muscles: the thyroarytenoid and posterior cricoarytenoid. Consequently, it is unknown whether the remaining intrinsic laryngeal muscles evidence this highly refined phenotype or if they retain a phenotype more similar to prototypical skeletal muscle. The purpose of this study was to further define the biologic properties of the interarytenoid (IA) and cricothyroid (CT) muscles of the larynx using the dystrophin deficient mdx mouse model. Previous work in this model has demonstrated sparing of select craniofacial muscles in the disease. Interestingly, a vast body of literature also supports the uniqueness of these spared muscles in a number of other areas including: fiber types, motor unit size, proprioceptive mechanisms, myosin isoform expression, remodeling behaviors, and sarcomeric structure. It follows, then, that muscle response to dystrophin deficiency serves as a sensitive marker of a muscles level of biological specialization and its similarity to or departure from classic limb muscle. Larynges and gastrocnemius muscles from 8 mdx and 8 C57BL control mice were examined histologically for typical markers of dystrophinopathy. Immunocytochemical testing examined the distribution of dystrophin and its homolog, utrophin, in control and mdx muscles. Results demonstrated that despite the absence of dystrophin, the laryngeal muscles did not show the classic markers of disease. The mdx superior cricoarytenoid muscle (SCA; mouse counterpart of human IA) demonstrated no evidence of damage, inflammation, necrosis, or regeneration. The mdx CT evidenced subtle markers of regeneration (eg, slight increase in centrally nucleated fibers) but no evidence of degeneration. The authors concluded that the SCA was spared from the effects of dystrophin deficiency, while the CT was strongly protected. The results demonstrate that the SCA and CT muscles of the larynx possess a specialized nature that separates them from prototypical limb muscle. Information from the study offers insight into the unique biology of the laryngeal muscles and holds implications for the translational study of voice and voice disorders.

No description available.

No description available.

Duchenne muscular dystrophy (DMD) and congenital muscular dystrophy 1A (MDC1A) are the two most common forms of muscular dystrophy in humans, caused by mutations in dystrophin and laminin α2 genes respectively. Both are severe forms of the disease that lead to premature death due and are both now known to have a significant effect on the central nervous system. This project investigated the role of both proteins involved in each of these diseases in cerebellar Purkinje cells of two murine models of disease: the mdx mouse a dystrophin-deficient model of DMD and the dy2J a laminin α2-deficient murine model of MDC1A. In the case of dystrophin further studies were undertaken in order to determine if increasing age had any effects on cerebellar function. It was found that there is no difference in electrophysiological characteristics (RMP, IR, eEPSP) of the cells when compared to appropriate control groups, nor was there any difference when young and aged dystrophin-deficient mdx groups were compared. Evoked IPSP characteristics were examined in young mdx cerebellar Purkinje cells and again no difference was found when compared to wildtype. There was a significant difference in response to the GABAA antagonist bicuculline, with wildtype increasing eEPSP amplitude by almost double that found in mdx. There was no difference in short term plasticity as measured by paired pulse facilitation in any of these groups. There was no difference in paired pulse depression at the inhibitory interneuron- Purkinje cell synapse of young wildtype and mdx cerebellar Purkinje cells. There a significant blunting of long term depression (LTD, (a form of long term synaptic plasticity) between young wildtype and mdx. When young wildtype animals were compared to aged wildtype animals LTD was found to be similar, when young mdx was compared to aged mdx, there was a recovery of LTD seen in the aged population. There was also significant differences in LTD found when littermate controls were compared to dy2J (laminin α2 mutants). A third of the phenotypic animals (dy2J) potentiated. Finally when rebound potentiation (a GABA-ergic form of long term synaptic plasticity in the cerebellum) was compared in young wildtype and mdx mice, mdx mice displayed depression, rather than the expected potentiation in contrast to potentiation (or no change) as seen in all wildtype cells.

alpha- and beta-dystroglycan (DG) were first identified as members of an oligomeric, transmembrane complex expressed in muscle and linking laminin (LN) in the extracellular matrix (ECM) to dystrophin in the submembraneous cytoskeleton. This dystrophin-associated glycoprotein complex (DGC) has been proposed to perform a structural role in skeletal muscle, its loss leading to loss of membrane integrity, muscle fiber degeneration and muscular dystrophy. alpha- and beta-DG appear to form the core of the DGC since alpha-DG is a high affinity LN receptor while beta-DG is a transmembrane protein that anchors alpha-DG to the membrane and interacts with dystrophin intracellularly. In order to determine the involvement of DG in skeletal muscle homeostasis and in LN assembly, we generated mouse muscle cell lines deficient in DG expression. Extensive characterization of these cells revealed that DG is essential for LN assembly on the surface of mature myotubes but that it is not involved in the maintenance of membrane integrity in culture. However, DG-deficient cells show increased apoptotic cell death during and after the period of myoblast differentiation into myotubes, indicating that DG is important for muscle cell survival. / The ECM molecule agrin has been implicated in the induction of acetylcholine receptor (AChR) aggregation at the neuromuscular junction (NMJ). The C-terminus of agrin shares significant homology with the region of LN that interacts with alpha-DG; we therefore reasoned that alpha-DG could be an agrin receptor. Ligand overlay assays revealed that alpha-DG binds agrin with high affinity and antibody perturbation experiments indicated that alpha-DG is involved in agrin-induced aggregation of AChRs. The role of alpha-DG in AChR aggregation was further studied using the DG deficient muscle cell lines. We found that alpha-DG is involved in the later stages of agrin-induced AChR aggregation. / We further localized DG and two of its intracellular ligands, dystrophin and its autosomal homologue utrophin, to a synaptic layer in the retina suggesting a role for DG in central nervous system synapses. DG, utrophin and LN are also co-expressed around blood vessels indicating a possible function in blood-brain barrier homeostasis.

Duchenne muscular dystrophy (DMD) is characterized by necrosis and progressive loss of muscle fibers. DMD patients have a mutation in the gene encoding dystrophin, a large membrane-associated cytoskeletal protein on the cytoplasmic side of the sarcolemma. Gene therapy using fully deleted adenoviral vectors shows great potential for the eventual treatment of DMD and other genetic diseases. These vectors are less immunogenic than their predecessors and have the capacity to carry large DNA inserts such as the full-length dystrophin (12 kb). However, the lack of viral genes results in a weakened and subsiding (short) transgene expression in muscle. Findings in the lung and liver have shown the adenoviral E4 region, in particular E4 open reading frame 3 (ORF3) to contribute to the maintenance of transgene expression. We constructed an adenovirus in which E4 ORF3 was reintroduced into a fully-deleted adenovirus along with full-length dystrophin (AdCBDysORF3). Dystrophin levels produced by AdCBDysORF3 were found to be not sustained in mdx mice, dropping significantly by day 90. However, expression levels did increase when AdCBDysORF3 was complemented with other viral proteins such as EIB. Likewise, increasing the expression of the primary adenovirus receptor (CAR) in muscle also resulted in a higher initial dystrophin expression in myofibers.

Doctor of Philosophy(PhD) / The vast majority of children undergoing surgical repair of cardiac lesions do spectacularly well. However a significant proportion, ~ 25%, struggle to progress in the early postoperative period and require additional pharmacological and occasionally mechanical circulatory support. All children typically have some degree of postoperative myocardial dysfunction, with the severe spectrum termed the low cardiac output state (LCOS). LCOS is clinically defined as the requirement for new or escalated inotrope therapy, a widened arteriovenous oxygen difference, cardiac arrest or the need for reinstitution of mechanical circulatory support. LCOS is largely responsible for the morbidity and mortality involved in paediatric cardiac surgery. Despite the predictability of LCOS in the initial postoperative hours, the underlying pathophysiology remains unclear. The period of decline in cardiac function that typifies LCOS is temporally associated with the development of oedema in the tissues of the body, including the heart. This relationship between oedema and dysfunction has increasingly become blurred, with a tendency to elevate the temporal association to a causal link. We sought to explore the causes and contributions to myocardial dysfunction in this setting, including the roles of oedema and ischaemia within the heart. In focusing on oedema and ischaemia we also examined the effects of these insults on relevant myocardial membrane proteins, including those that permit rapid water transport – aquaporins (AQPs), and those involved in membrane mechanics – dystrophin, and membrane repair – dysferlin. Experimental settings which enabled the in vitro dissection of these insults and proteins of interest were combined with a clinically accurate in vivo model. This thesis describes a series of thematically linked experiments that examined LCOS, myocardial oedema and the role of various membrane proteins. We performed isolated cardiomyocyte studies, isolated heart studies as well as a clinically relevant large animal (lamb) cardiopulmonary bypass (CPB) model. Across these models we also explored the role of therapeutically protecting myocardial membranes with Poloxamer 188 (P188) and assessed any influence on myocardial function, oedema and membrane proteins. vi The results from these three models suggest that the clinically accepted dogma of a causative link between myocardial oedema and dysfunction overstates the contribution of myocardial oedema to LCOS. We found that ischaemia/reperfusion was of primary importance in causing myocardial dysfunction. Myocardial oedema without ischaemia had a mild and reversible contribution to myocardial dysfunction, but this was minor in comparison to the gross dysfunction attributable to ischaemia. Isolated cardiomyocytes, with induced oedema, functioned well. Whilst ischaemic cardiomyocytes, with less swelling still had severe contractile dysfunction. Isolated hearts, perfused with an oedema inducing crystalloid perfusate developed myocardial oedema and had minimal reversible systolic and diastolic dysfunction. Isolated hearts which experienced global ischaemia had comparable degrees of myocardial oedema, and significantly greater degrees of myocardial dysfunction that increased in severity with increasing duration of ischaemia. In the lamb CPB model, only those lambs which underwent aortic cross clamping and had a period of ischaemia had poor myocardial function. These lambs also had swollen hearts, raised myocardial AQP1 mRNA and reduced membrane dysferlin protein expression. Membrane dystrophin protein expression was not altered, somewhat unexpectedly with CPB with or without ischaemia. Lambs placed on CPB without ischaemia had good myocardial function, minimal oedema and unchanged membrane protein expression during the survival period. In a blinded lamb CPB trial of P188 there were improved haemodynamics and indicies of myocardial function associated with its use. This was also associated with preservation of dysferlin expression and reduced membrane injury. In parallel isolated heart trials of this therapy, there was a reduction in myocardial oedema associated with its use in non-ischaemic experiments. There was also a suggestion of improved diastolic function in ischaemic experiments, but no change in myocardial water content. In conclusion, we have highlighted the primacy of ischaemia/reperfusion over oedema in contributing to LCOS. We have refuted the accepted dogma that myocardial oedema causes significant dysfunction in itself, with important oedema likely to result from ischaemia. We have shown that AQP1 may be involved in the pathogenesis of the capillary leak syndrome. Finally we have hinted at a role for prophylactic P188 in the vii setting of LCOS, possibly highlighting the role of membrane repair in recovery after surgery. Isolated heart trials of P188 further support a non-rheological mechanism of action and also lend support to the causal separation of myocardial oedema and dysfunction. The integral membrane protein dysferlin, rather than dystrophin, is relevant in the setting of LCOS in the current era.

Duchenne muscular dystrophy (DMD) and congenital muscular dystrophy 1A (MDC1A) are the two most common forms of muscular dystrophy in humans, caused by mutations in dystrophin and laminin α2 genes respectively. Both are severe forms of the disease that lead to premature death due and are both now known to have a significant effect on the central nervous system. This project investigated the role of both proteins involved in each of these diseases in cerebellar Purkinje cells of two murine models of disease: the mdx mouse a dystrophin-deficient model of DMD and the dy2J a laminin α2-deficient murine model of MDC1A. In the case of dystrophin further studies were undertaken in order to determine if increasing age had any effects on cerebellar function. It was found that there is no difference in electrophysiological characteristics (RMP, IR, eEPSP) of the cells when compared to appropriate control groups, nor was there any difference when young and aged dystrophin-deficient mdx groups were compared. Evoked IPSP characteristics were examined in young mdx cerebellar Purkinje cells and again no difference was found when compared to wildtype. There was a significant difference in response to the GABAA antagonist bicuculline, with wildtype increasing eEPSP amplitude by almost double that found in mdx. There was no difference in short term plasticity as measured by paired pulse facilitation in any of these groups. There was no difference in paired pulse depression at the inhibitory interneuron- Purkinje cell synapse of young wildtype and mdx cerebellar Purkinje cells. There a significant blunting of long term depression (LTD, (a form of long term synaptic plasticity) between young wildtype and mdx. When young wildtype animals were compared to aged wildtype animals LTD was found to be similar, when young mdx was compared to aged mdx, there was a recovery of LTD seen in the aged population. There was also significant differences in LTD found when littermate controls were compared to dy2J (laminin α2 mutants). A third of the phenotypic animals (dy2J) potentiated. Finally when rebound potentiation (a GABA-ergic form of long term synaptic plasticity in the cerebellum) was compared in young wildtype and mdx mice, mdx mice displayed depression, rather than the expected potentiation in contrast to potentiation (or no change) as seen in all wildtype cells.

Doctor of Philosophy(PhD) / The vast majority of children undergoing surgical repair of cardiac lesions do spectacularly well. However a significant proportion, ~ 25%, struggle to progress in the early postoperative period and require additional pharmacological and occasionally mechanical circulatory support. All children typically have some degree of postoperative myocardial dysfunction, with the severe spectrum termed the low cardiac output state (LCOS). LCOS is clinically defined as the requirement for new or escalated inotrope therapy, a widened arteriovenous oxygen difference, cardiac arrest or the need for reinstitution of mechanical circulatory support. LCOS is largely responsible for the morbidity and mortality involved in paediatric cardiac surgery. Despite the predictability of LCOS in the initial postoperative hours, the underlying pathophysiology remains unclear. The period of decline in cardiac function that typifies LCOS is temporally associated with the development of oedema in the tissues of the body, including the heart. This relationship between oedema and dysfunction has increasingly become blurred, with a tendency to elevate the temporal association to a causal link. We sought to explore the causes and contributions to myocardial dysfunction in this setting, including the roles of oedema and ischaemia within the heart. In focusing on oedema and ischaemia we also examined the effects of these insults on relevant myocardial membrane proteins, including those that permit rapid water transport – aquaporins (AQPs), and those involved in membrane mechanics – dystrophin, and membrane repair – dysferlin. Experimental settings which enabled the in vitro dissection of these insults and proteins of interest were combined with a clinically accurate in vivo model. This thesis describes a series of thematically linked experiments that examined LCOS, myocardial oedema and the role of various membrane proteins. We performed isolated cardiomyocyte studies, isolated heart studies as well as a clinically relevant large animal (lamb) cardiopulmonary bypass (CPB) model. Across these models we also explored the role of therapeutically protecting myocardial membranes with Poloxamer 188 (P188) and assessed any influence on myocardial function, oedema and membrane proteins. vi The results from these three models suggest that the clinically accepted dogma of a causative link between myocardial oedema and dysfunction overstates the contribution of myocardial oedema to LCOS. We found that ischaemia/reperfusion was of primary importance in causing myocardial dysfunction. Myocardial oedema without ischaemia had a mild and reversible contribution to myocardial dysfunction, but this was minor in comparison to the gross dysfunction attributable to ischaemia. Isolated cardiomyocytes, with induced oedema, functioned well. Whilst ischaemic cardiomyocytes, with less swelling still had severe contractile dysfunction. Isolated hearts, perfused with an oedema inducing crystalloid perfusate developed myocardial oedema and had minimal reversible systolic and diastolic dysfunction. Isolated hearts which experienced global ischaemia had comparable degrees of myocardial oedema, and significantly greater degrees of myocardial dysfunction that increased in severity with increasing duration of ischaemia. In the lamb CPB model, only those lambs which underwent aortic cross clamping and had a period of ischaemia had poor myocardial function. These lambs also had swollen hearts, raised myocardial AQP1 mRNA and reduced membrane dysferlin protein expression. Membrane dystrophin protein expression was not altered, somewhat unexpectedly with CPB with or without ischaemia. Lambs placed on CPB without ischaemia had good myocardial function, minimal oedema and unchanged membrane protein expression during the survival period. In a blinded lamb CPB trial of P188 there were improved haemodynamics and indicies of myocardial function associated with its use. This was also associated with preservation of dysferlin expression and reduced membrane injury. In parallel isolated heart trials of this therapy, there was a reduction in myocardial oedema associated with its use in non-ischaemic experiments. There was also a suggestion of improved diastolic function in ischaemic experiments, but no change in myocardial water content. In conclusion, we have highlighted the primacy of ischaemia/reperfusion over oedema in contributing to LCOS. We have refuted the accepted dogma that myocardial oedema causes significant dysfunction in itself, with important oedema likely to result from ischaemia. We have shown that AQP1 may be involved in the pathogenesis of the capillary leak syndrome. Finally we have hinted at a role for prophylactic P188 in the vii setting of LCOS, possibly highlighting the role of membrane repair in recovery after surgery. Isolated heart trials of P188 further support a non-rheological mechanism of action and also lend support to the causal separation of myocardial oedema and dysfunction. The integral membrane protein dysferlin, rather than dystrophin, is relevant in the setting of LCOS in the current era.