Somatostatin Receptor Ligand Stimulates Mitochondrial Biogenesis and Oxidative Phosphorylation in Mouse Skeletal Muscle

Presentation Number: SUN 270
Date of Presentation: April 2nd, 2017

Anat Ben-Shlomo*, Allen Andres, Evelyn Ding, Masaaki Yamamoto, Ramtin Khalafi, Shawn Wagner, Jean-Philippe Vit, Wei Yang and Roberta Gottlieb
Cedars-Sinai Medical Center, Los Angeles, CA

Abstract

Human skeletal muscle (SkM) expresses somatostatin receptors (SSTs), but little is known about somatostatin effects on SkM action. SkM loss and myopathy is caused by inflammatory, infectious, hormonal, neurological and drug (statins, HIV and immunosuppressive drugs) related diseases. The somatostatin receptor ligand pasireotide (PASI), which binds multiple SSTs (SST5 > SST2 > SST3 > SST1), is used in patients with Cushing disease, who commonly exhibit myopathy. We sought to study effects of PASI on SkM by assessing mitochondrial biogenesis and oxidative phosphorylation (OXPHOS). On qRT-PCR and Western blot, human HSMM primary myotubes expressed SST1, 2 and 5. Mouse tibialis anterior muscle (TAM), a fast-twitch fiber type providing power, soleus muscle, a mitochondria-rich, slow-twitch fiber type providing endurance, as well as mouse C2C12 myotubes expressed SST2, 3 and 4 on qRT-PCR, and C2C12 intracellular cAMP levels dose-dependently decreased upon PASI treatment. C57Bl/6J male mice were treated with vehicle or PASI (long-acting release 40 mg/kg) every 2 weeks for 0.25, 3.5, or 7 months. PASI reduced circulating IGF-1 levels, by 44% at 3.5 months and 28% at 7 months (p=0.001). Hind limb SkM volume measured by MRI was reduced 22% (p=0.0001) after 1 week of treatment but only 10% after 7 months. Fiber size measured by IHC was reduced by 3.2% (ImageJ, MinFeret) (p=0.006) after 1 week, by 13% at 3.5 months, and 10% at 7 months. Four-limb grip test demonstrated 6.8% decrease (p=0.01) in the power generated by fast-twitch SkM fiber after 7 months of PASI treatment, but no change was observed in 60-minute open field test activity or rotor rod test performance. Despite causing mildly decreased SkM mass and power, PASI induced SkM mitochondrial biogenesis and increased OXPHOS in both soleus and TAM. Increased expression of multiple mitochondrial genes and proteins was demonstrated by proteomics and qRT-PCR. Western blot demonstrated increased mitochondrial membrane protein COX4 and TOM70 expression and OXPHOS proteins, as well as a 21-fold increased mitochondrial to nuclear DNA ratio. Bioenergetics analysis of isolated SkM mitochondria (Seahorse) demonstrated increased maximal oxygen consumption rate in TAM mitochondria in 3 of 5 mice and in soleus mitochondria in 2 of 5 mice, but in 0 of 5 mouse hearts. OXPHOS protein NDUFB8 expression positively correlated with GHR expression in both SkM types (r=0.6, p=0.0002 in TAM and r=0.59, p=0.004 in soleus) and negatively correlated with glucocorticoid receptor (NC3R1) in TAM (r=-0.41, p=0.04). Our results show that PASI stimulates mitochondrial biogenesis and OXPHOS in mouse SkM at the expense of mild non-progressive decrease in SkM mass and power. PASI may attenuate myopathy outcomes by promoting fiber type transition and increased endurance.

 

Nothing to Disclose: AB, AA, ED, MY, RK, SW, JPV, WY, RG