Globular adiponectin induces differentiation and fusion of skeletal muscle cells

Local induction of adiponectin reduces lipopolysaccharide-triggered skeletal muscle damage

Adiponectin (ApN) exhibits metabolic and antiinflammatory properties. This hormone is exclusively secreted by adipocytes under normal conditions. We have shown that ApN was induced in tibialis anterior muscle of mice injected with lipopolysaccharide (LPS) and in C2C12 myotubes cultured with proinflammatory cytokines. We hypothesized that muscle ApN could be a local protective mechanism to counteract excessive inflammatory reaction and oxidative damage. To test this paradigm, we examined whether muscles of ApN-knockout (KO) mice exhibit a higher degree of oxidative stress and apoptosis than wild-type mice when challenged by ip LPS and whether these abnormalities may be corrected by local administration of ApN. Eventually we investigated the effects of ApN in vitro. When compared with wild-type mice, ApN-KO mice exhibited myocyte degenerescence, especially after LPS. Myocytes of ApN-KO mice also displayed much stronger immunolabeling for markers of oxidative stress (peroxiredoxin-3/5 and heme oxygenase-1) as well as for a lipid peroxidation product (hydroxynonenal). Expression of TNF-α, caspase-6, a marker of apoptosis, and nuclear factor-κB was enhanced as well. Eventually muscle electrotransfer of the ApN gene, which did not induce any rise of systemic ApN, corrected all these abnormalities in LPS-injected ApN-KO mice. Likewise, ApN attenuated LPS-induced production of proinflammatory cytokines and activation of nuclear factor-κB in C2C12 cells. Thus, induction of ApN into skeletal muscle in response to an inflammatory aggression appears to be a crucial mechanism to counteract in an autocrine or paracrine fashion excessive inflammatory damage, oxidative stress, and subsequent apoptosis.

Adiponectin action from head to toe

Adiponectin, the most abundant protein secreted by white adipose tissue, is known for its involvement in obesity-related disorders such as insulin resistance, type 2 diabetes mellitus and atherosclerosis. Moreover, modulation of the circulating adiponectin concentration is observed in pathologies that are more or less obesity-related, such as cancer and rheumatoid arthritis. The wide distribution of adiponectin receptors in various organs and tissues suggests that adiponectin has pleiotropic effects on numerous physiological processes. Besides its well-known insulin-sensitizing, anti-inflammatory and antiatherosclerotic properties, accumulating evidence suggests that adiponectin may also have anticancer properties and be cardioprotective. A beneficial effect of adiponectin on female reproductive function was also suggested. Since adiponectin has numerous beneficial biological functions, its use as a therapeutic agent has been suggested. However, the use of adiponectin or its receptors as therapeutic targets is complicated by the presence of different adiponectin oligomeric isoforms and production sites, by multiple receptors with differing affinities for adiponectin isoforms, and by cell-type-specific effects in different tissues. In this review, we discuss the known and potential roles of adiponectin in various tissues and pathologies. The therapeutic promise of administration of adiponectin and the use of its circulating levels as a diagnostic biomarker are further discussed based on the latest experimental studies.

Globular adiponectin as a complete mesoangioblast regulator: role in proliferation, survival, motility, and skeletal muscle differentiation

This article shows that globular adiponectin regulates vital cues of mesoangioblast, such as proliferation, survival, and migration toward myotubes and the myogenic properties. In vivo experiments confirm that globular adiponectin increases the survival, engraftment, and localization to muscle of mesoangioblasts in α-sarcoglycan-null mice.

Mesoangioblasts are progenitor endowed with multipotent mesoderm differentiation ability. Despite the promising results obtained with mesoangioblast transplantation in muscle dystrophy, an improvement of their efficient engrafting and survival within damaged muscles, as well as their ex vivo activation/expansion and commitment toward myogenic lineage, is highly needed and should greatly increase their therapeutic potential. We show that globular adiponectin, an adipokine endowed with metabolic and differentiating functions for muscles, regulates vital cues of mesoangioblast cell biology. The adipokine drives mesoangioblasts to entry cell cycle and strongly counteracts the apoptotic process triggered by growth factor withdrawal, thereby serving as an activating and prosurvival stem cell factor. In addition, adiponectin provides a specific protection against anoikis, the apoptotic death due to lack of anchorage to extracellular matrix, suggesting a key protective role for these nonresident stem cells after systemic injection. Finally, adiponectin behaves as a chemoattractive factor toward mature myotubes and stimulates their differentiation toward the skeletal muscle lineage, serving as a positive regulator in mesoangioblast homing to injured or diseased muscles. We conclude that adiponectin exerts several advantageous effects on mesoangioblasts, potentially valuable to improve their efficacy in cell based therapies of diseased muscles.