Absence of Functional Leptin Receptor Isoforms in the POUND (Leprdb/lb) Mouse Is Associated with Muscle Atrophy and Altered Myoblast Proliferation and Differentiation

Abstract

ObjectiveLeptin receptors are abundant in human skeletal muscle, but the role of leptin in muscle growth, development and aging is not well understood. Here we utilized a novel mouse model lacking all functional leptin receptor isoforms (POUND mouse, Leprdb/lb) to determine the role of leptin in skeletal muscle.Methods and FindingsSkeletal muscle mass and fiber diameters were examined in POUND mice, and primary myoblast cultures were used to determine the effects of altered leptin signaling on myoblast proliferation and differentiation. ELISA assays, integrated pathway analysis of mRNA microarrays, and reverse phase protein analysis were performed to identify signaling pathways impacted by leptin receptor deficiency. Results show that skeletal muscle mass and fiber diameter are reduced 30–40% in POUND mice relative to wild-type controls. Primary myoblast cultures demonstrate decreased proliferation and decreased expression of both MyoD and myogenin in POUND mice compared to normal mice. Leptin treatment increased proliferation in primary myoblasts from muscles of both adult (12 months) and aged (24 months) wild-type mice, and leptin increased expression of MyoD and myogenin in aged primary myoblasts. ELISA assays and protein arrays revealed altered expression of molecules associated with the IGF-1/Akt and MAPK/MEK signaling pathways in muscle from the hindlimbs of mice lacking functional leptin receptors.ConclusionThese data support the hypothesis that the adipokine leptin is a key factor important for the regulation of skeletal muscle mass, and that leptin can act directly on its receptors in peripheral tissues to regulate cell proliferation and differentiation.

Whole-Body Vibration Mimics the Metabolic Effects of Exercise in Male Leptin Receptor–Deficient Mice

“…Paraffin sections were stained with H&E, and minimal fiber diameters were calculated in ImageJ, as previously described (34). To quantify hepatic lipid content, liver samples were weighed, homogenized, and processed for chloroform extraction (41).…”

The aromatic amino acid tryptophan stimulates skeletal muscle IGF1/p70s6k/mTor signaling in vivo and the expression of myogenic genes in vitro

“…Myostatin (Cat # K1012) ELISA kits were purchased from Alpco diagnostic and performed according to manufacturer’s protocol as we have described previously [21]. Frozen sections of the EDL muscle were stained using primary antibodies to follistatin (goat anti-human polyclonal, R&D Systems clone AF-669) and IGF-1 (rabbit anti-human polyclonal, Santa Cruz Biotechnology clone H-70) with donkey anti-goat Alexa Fluor 488 (abcam ab150129) and goat anti-rabbit Alexa Fluor 546 (Life Technologies A11010) secondary antibodies following procedures we have described previously [22]. …”

“…qRT-PCR analysis of C2C12 cells was performed as described previously [21, 22]. Briefly, cells were lysed in TRIzol® reagent (Invitrogen) for RNA isolation and subsequent cDNA synthesis (iScript ™ kit; Bio-Rad, Hercules, CA, USA).…”

Differential control of muscle mass in type 1 and type 2 diabetes mellitus

“…In addition, enhanced muscle expression of myostatin is detected in db/db mice, and in this regard, genetic ablation of myostatin increases muscle mass in these animals, although it does not completely rescue the defects of diabetes [155]. POUND mice, which lack all leptin receptor isoforms, also show reduced muscle mass [156].…”