Gαi2 Signaling Is Required for Skeletal Muscle Growth, Regeneration, and Satellite Cell Proliferation and Differentiation

Abstract

eWe have previously shown that activation of G␣i2, an ␣ subunit of the heterotrimeric G protein complex, induces skeletal muscle hypertrophy and myoblast differentiation. To determine whether G␣i2 is required for skeletal muscle growth or regeneration, G␣i2-null mice were analyzed. G␣i2 knockout mice display decreased lean body mass, reduced muscle size, and impaired skeletal muscle regeneration after cardiotoxin-induced injury. Short hairpin RNA (shRNA)-mediated knockdown of G␣i2 in satellite cells (SCs) leads to defective satellite cell proliferation, fusion, and differentiation ex vivo. The impaired differentiation is consistent with the observation that the myogenic regulatory factors MyoD and Myf5 are downregulated upon knockdown of G␣i2. Interestingly, the expression of microRNA 1 (miR-1), miR-27b, and miR-206, three microRNAs that have been shown to regulate SC proliferation and differentiation, is increased by a constitutively active mutant of G␣i2 [G␣i2(Q205L)] and counterregulated by G␣i2 knockdown. As for the mechanism, this study demonstrates that G␣i2(Q205L) regulates satellite cell differentiation into myotubes in a protein kinase C (PKC)-and histone deacetylase (HDAC)-dependent manner. Heterotrimeric G proteins are intracellular proteins and transduce external signals from a variety of cell surface receptors to intracellular effectors (1). G proteins are classified according to their ␣ subunits into four subfamilies: G␣s, G␣i/o, G␣q/11, and G␣ 12/13 (1). The G␣i subfamily is encoded by three genes, GNAI1, GNAI2, and GNAI3, and was originally identified by its ability to inhibit adenylyl cyclase activity. All three G␣i isoforms have been deleted by gene targeting in mice, and the resulting phenotypes indicate that they have both overlapping and distinct functions. Ablation of G␣i1 in mice modulates adenylyl cyclase activity in the hippocampus and impairs memory formation (2). G␣i2-deficient mice display growth retardation, develop ulcerative colitis (3), and present defects of the parasympathetic heart rate (4), while G␣i3 has been shown to modulate insulin regulation of autophagy in hepatocytes (5) and to be required for normal patterning of the axial skeleton (6) and for cytoskeleton-dependent control of cilium migration as an important step in establishing planar cell polarity in cochlear cells (7). However, the requirement for G␣i isoforms in skeletal muscle growth and regeneration has not been determined.Mammalian skeletal muscle has the ability to regenerate and repair in response to exercise or injury. Regeneration of skeletal muscle is mainly executed by satellite cells (SCs) (8). SCs are a population of muscle stem cells that reside between the sarcolemma and the basal lamina. In neonatal muscle, growth is mainly achieved by addition of myoblasts derived from SCs to existing myofibers (9, 10). In the adult muscle, SCs-quiescent under normal physiological conditions-are activated in response to trauma and are able to self-renew, proliferate, and differentiate to fuse to damaged fibers or fo...

Skeletal Muscle Abnormalities in Heart Failure

“…75) Skeletal muscle atrophy has been observed in Gα Sdeficient mice. 76) Conversely, in a recent study, skeletal muscle hypertrophy was observed through a PKC signal mediated by Gα i 2 activation. 76) Gα i 2 activation phosphorylated the downstream target of mTOR, particularly p70S6K and GSK3β, but not Akt.…”

Biased Agonism of Three Different Cannabinoid Receptor Agonists in Mouse Brain Cortex

“…The Gα i subfamily members Gα i1 , Gα i2 , and Gα i3 were originally identified by their ability to inhibit AC activity (Plummer et al, 2012; Busnelli et al, 2013; Minetti et al, 2014). Our results show that Δ 9 -THC, WIN55212-2, and ACEA significantly stimulate Gα i1 subunit.…”

The AKT/mTOR signaling pathway plays a key role in statin-induced myotoxicity

“…To analyze changes in myotube diameter, myotubes were stained following the protocol of Minetti et al [25]. Briefly, myotubes were fixed with 4% PFA (Paraformaldehyde) and permeabilized with 0.2% Triton.…”