Aims/hypothesis Adiponectin and leptin are negatively and positively correlated with human obesity respectively, and have both been shown to regulate energy metabolism in skeletal muscle. However, little is known about their signalling and functional crosstalk. Here we investigated the effects of leptin on metabolic actions of (1) globular adiponectin (gAd) and (2) full-length adiponectin (fAd) in L6 cells. Methods Glucose uptake was measured upon gAd and fAd treatment after incubation with different doses (0.3, 0.6, 3, 6, 60 nmol/l) of leptin for 6, 12 and 24 h. We also measured adiponectin receptor (ADIPOR) expression and stimulation of downstream signalling by gAd and fAd using coimmunoprecipitation and western blotting following leptin pretreatment, as well as analysis of fatty acid uptake and oxidation using radiolabelled tracers. Results Leptin attenuated the stimulation of glucose uptake by gAd and fAd in a dose-and time-dependent manner, a finding correlated with decreased levels of ADIPOR1 and ADIPOR2. gAd and fAd increased palmitate uptake via activation of AMP protein kinase (T172), enhanced expression of the fatty acid transporter CD36, phosphorylated acetyl-CoA carboxylase (S79) and enhanced palmitate oxidation, all of which were attenuated by leptin pretreatment. Adiponectin can also enhance insulin sensitivity via direct signalling crosstalk; here we show that enhanced insulin-stimulated IRS-1 (Y612) and Akt (T308) phosphorylation in response to fAd was attenuated by leptin. APPL1 was recently identified as a critical mediator of adiponectin action in skeletal muscle. We demonstrated that leptin attenuated binding of APPL1 to LKB1, a downstream target leading to AMPK phosphorylation. Conclusions/interpretation The direct metabolic and insulin-sensitising effects of adiponectin were attenuated in the presence of leptin.

Adiponectin and leptin have been shown to regulate energy metabolism in skeletal muscle. However, little is known regarding their signaling crosstalk. Hyperleptinemia is a common feature in human obesity and here we investigated effects of leptin (60 nM, 24 hours) on functions of recombinant globular (gAd) and full‐length multimers (fAd) of adiponectin in L6 skeletal muscle cells.Real‐time PCR showed that mRNA expression levels of adiponectin receptor 1 (AdipoR1) and AdipoR2 were reduced after leptin treatment. Correspondingly, effects of both gAd and fAd on glucose and fatty acid uptake and oxidation were attenuated. AMPK is thought to be an important mediator of metabolic effects of adiponectin and here we showed that Compound C (AMPK inhibitor) pretreatment prevented stimulation of fatty acid uptake by fAd. Importantly, the activation of AMPK and ACC by gAd and fAd was attenuated by leptin. APPL1 was recently identified as an adaptor protein interacting with AdipoR and downstream targets such as Akt. Here we observed that leptin also regulated Ad‐stimulated binding of APPL1 to these targets.These results suggest that hyperleptinemia can induce resistance to gAd and fAd in skeletal muscle cells, possibly due to the reduction of AdipoR expression.