Endocrine Abstracts

Purpose of study: Skeletal muscle wasting is a serious public health problem associated with aging, chronic kidney disease, and AIDS. Vitamin D (VD) is most widely recognised for its regulation of calcium and phosphate homeostasis in relation to bone development and maintenance and for its synergistic effects on target organs such as PTH glands. Recently, it has been shown to improve muscle performance and reduce falls in VD deficient older adults. However, little is known of the underlying molecular mechanism or the role it plays in association with myogenic differentiation and on muscle fibrosis. We examined the effect of 1,25-D₃ -the active form of VD- on myogenic cell differentiation and on the generation of an anti-fibrotic phenotype in skeletal muscle derived cells.

Methods: Primary cultures of skeletal muscle derived satellite cells and fibroblasts were isolated from the tibialis anterior, soleus and gastrocnemius muscles of 2-month-old C57/BL6 male mice and then treated with or without 1,25-D₃ in a time course manner. Expression of vitamin D receptor (VDR), collagen I, III, pro and anti-fibrotic factors, muscle lineage and angiogenic markers were assessed by ICC, IF, PCR arrays and confirmed by real time qPCR and western blots.

Summary: The efficiency of satellite cells isolation determined by PAX-7⁺ cells was 86%. It was confirmed that Satellite cells expressed VDR. Addition of 1,25-D₃ (100nM) to satellite cells induces: i) increase expression of Troponin-I and II, ii) increase expression of IGF-I and IGF-II, iii) increase expression of Follistatin (−a Myostatin inhibitor) and iv) a decrease expression of Mstn (Myostatin- a key negative regulator of muscle mass). Fibroblast isolated with a 90% efficiency determined by Vimentin⁺ and α-SMA⁻ cells showed a decreased expression of collagen I and III after being challenged with TGF-β alone or in combination with 1,25-D₃.

Conclusion: Vitamin D posses a clear myogenic effect on satellite cells (adult muscle stem cells) in charge of reconstitute the muscle after muscle injury or muscle waste. It also posses an anti-fibrotic effect on fibroblast of muscle origin. This study provides a mechanistic justification for VD replenishment in muscle waste conditions such as AIDS, cancer, congestive heart failure, renal failure, characterized by lost of muscle mass and excessive collagen deposition (fibrotic process) and also in VD deficient older adults who are known to have age-related loss of muscle mass and strength and an increased rate of falls.