Globular adiponectin activates Akt in cultured myocytes

The serine/threonine kinase Akt plays an important role in insulin-mediated glucose uptake. Adiponectin (Adp) is known to sensitize this process. The purpose of the current study is to investigate if Adp activates Akt independently from insulin; and if Adp synergizes with insulin on Akt phosphorylation in the rat skeletal muscle L6 cells. Differentiated L6 cells were serum-starved and exposed to various concentrations (0–100 nM) of recombinant globular Adp (gAdp) and/or insulin for different time periods at 37 °C. Phosphorylation of Akt was monitored by Western blot using an antiserum against pSer473 or pThr308 Akt. The results demonstrate that gAdp activates Akt in dose- and time-dependent manners. When L6 cells were treated with sub-maximal concentrations of both insulin (10 nM) and gAdp (10 nM) for 10 min neither synergistic nor additive activation of Akt was observed. Similar non-synergistic or non-additive effect of gAdp on insulin-induced Akt activation was also observed in mouse C2C12 myocytes and rat vascular smooth muscle PAC cells. Moreover, pretreatment of the L6 cells with wortmannin (100 nM) for 20 min significantly reduced gAdp (100 nM) induced and insulin (100 nM) induced Akt activation by ∼80 and ∼70%, respectively. These data suggest that adiponectin stimulates Akt activation via the wortmannin sensitive pathway in L6 cells; and that its effects on Akt phosphorylation are not additive to those of insulin.

► Globular adiponectin activates Akt in muscle cell lines.
► Globular Adp activates Akt via a wortmannin sensitive pathway.
► Adp does not enhance insulin-induced Akt activation in muscle cells.
► Adp and insulin activate Akt via a shared intracellular pathway.