Characterizing the Role of Phospholamban in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) and the murine model, mdx, are recessive X-linked myopathies characterized by aberrant Ca2+-handling resulting in muscle atrophy and weakness. Phospholamban (PLN) is a protein inhibitor of sarco(endo)plasmic reticulum Ca2+-ATPases (SERCAs) that physically interacts with SERCA to regulate Ca2+-handling. Targeted therapy to improve SERCA function is a proven strategy to alleviate DMD in mdx mice.  In this study, Pln-/- mice were crossed with mdx mice to generate mdx/Pln-/- double knockout mutant mice.  Since PLN inhibits SERCAs, it was hypothesized that PLN ablation would mitigate Ca2+ dysregulation and rescue the dystrophic phenotype. Soleus and diaphragm muscles from WT, mdx/Pln+/+ and mdx/Pln-/- mice were excised to determine differences in the muscle morphology and functionality. Histological analysis revealed stark increases in the proportion of centralized nuclei and collagen invasion in mdx/Pln-/- and mdx mice compared to WT, however, there were no differences in these markers between mdx groups. Immunofluorescence staining demonstrated that both soleus and diaphragm from mdx/Pln-/- mice shifted towards type IIB and type IIX fibre types, as the proportion of these fibres were significantly greater than mdx/Pln+/+ and WT. This shift was accompanied by increased cross sectional area of type IIB fibres in mdx/Pln-/- compared to mdx/Pln+/+. Western blotting analysis of soleus and diaphragm muscle homogenate showed an increase inexpression of the SERCA regulator, sarcolipin (SLN), in both mdx groups relative to WT, however, there was a significant decline in SLN content in mdx/Pln-/- compared to mdx/Pln+/+. Additionally, there was a significant elevation in PLN content in mdx/Pln+/+ relative to WT in the soleus muscle. The solei of mdx/Pln+/+ and mdx/Pln-/- mice exhibited a significant reduction in force production compared to their WT counterparts at all frequencies when normalized to cross sectional area.  Unexpectedly, the force generated by mdx/Pln-/- soleus was significantly decreased at all stimulation frequencies when compared to mdx/Pln+/+. Furthermore, there was a significant reduction in soleus and diaphragm Ca2+ uptake in both the mdx/Pln+/+ and mdx/Pln-/- groups compared to WT, and surprisingly the rate of Ca2+ uptake was significantly lower in mdx/Pln-/- muscles compared with mdx/Pln+/+. Interestingly, while there were differences in SERCA mediated Ca2+ uptake between experimental groups, there were no significant differences in Ca2+- ATPase activity between WT, mdx/Pln+/+ and mdx/Pln-/- groups in the soleus and diaphragm muscles. Overall, these results demonstrate that PLN ablation in the mdx mouse model resulted in a worsening of the disease phenotype, as evident by elevations in centralized nucleation, a reduction in the ability to generate force and impairments in SERCA mediated Ca2+ uptake. These results suggest that PLN could potentially provide stabilization of the SERCA structure and function during oxidative stress

GDF15 promotes weight loss by enhancing energy expenditure in muscle

Funding Information: We thank R. Seeley for sharing GFRAL-null mice; B. Lowell for sharing β-less mice; and J. Wu for shipping β-less mice to us. G.R.S. was supported by a Diabetes Canada Investigator Award (DI-5-17-5302-GS), a Canadian Institutes of Health Research Foundation Grant (201709FDN-CEBA-116200), a Tier 1 Canada Research Chair in Metabolic Diseases and a J. Bruce Duncan Endowed Chair in Metabolic Diseases; D.W. by Fellowship Grants from the McMaster Institute for Research on Aging (MIRA) at McMaster University; S.R. by a postdoctoral fellowship supported by MITACS and Novo Nordisk; L.K.T. by a CIHR Post-Doctoral Fellowship Award and Michael DeGroote Fellowship Award in Basic Biomedical Science; E.M.D. by a Vanier Canada Graduate Scholarship; G.P.H. by the Natural Sciences and Engineering Research Council of Canada (NSERC: 400362); G.J.D. and S.M.F. by NSERC-CGSM scholarships; L.D. by the Fonds de Recherche du Québec-Santé doctoral training award; D.P.B. by the GSK Chair in Diabetes of Université de Sherbrooke and a FRQS J1 salary award. The Genotype-Tissue Expression (GTEx) Project was supported by the Common Fund of the Office of the Director of the National Institutes of Health, and by the NCI, NHGRI, NHLBI, NIDA, NIMH and NINDS. Funding Information: S.B.J. and R.E.K. are employees of Novo Nordisk, a pharmaceutical company producing and selling medicine for the treatment of diabetes and obesity. G.R.S. is a co-founder and shareholder of Espervita Therapeutics. McMaster University has received funding from Espervita Therapeutics, Esperion Therapeutics, Poxel Pharmaceuticals and Nestle for research conducted in the laboratory of G.R.S. S.R. is supported by a MITACS postdoctoral fellowship sponsored by Novo Nordisk. H.C.G. holds the McMaster-Sanofi Population Health Institute Chair in Diabetes Research and Care. G.R.S., G.P. and H.C.G. are inventors listed on a patent for identifying GDF15 as a biomarker for metformin. G.R.S. has received consulting/speaking fees from Astra Zeneca, Eli Lilly, Esperion Therapeutics, Merck, Poxel Pharmaceuticals and Cambrian Biosciences. The other authors declare no competing interests. Publisher Copyright: © 2023, The Author(s).Peer reviewedPublisher PD

The sarcoplasmic reticulum and SERCA: a nexus for muscular adaptive thermogenesis

We are currently facing an “obesity epidemic” worldwide. Promoting inefficient metabolism in muscle represents a potential treatment for obesity and its complications. Sarco(endo)plasmic reticulum (SR) Ca2+-ATPase (SERCA) pumps in muscle are responsible for maintaining low cytosolic Ca2+ concentration through the ATP-dependent pumping of Ca2+ from the cytosol into the SR lumen. SERCA activity has the potential to be a critical regulator of body mass and adiposity given that it is estimated to contribute upwards of 20% of daily energy expenditure. More interestingly, this fraction can be modified physiologically in the face of stressors, such as ambient temperature and diet, through its physical interaction with several regulators known to inhibit Ca2+ uptake and muscle function. In this review, we discuss advances in our understanding of Ca2+-cycling thermogenesis within skeletal muscle, focusing on SERCA and its protein regulators, which were thought previously to only modulate muscular contractility.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author