Conditioned medium from contracting skeletal muscle cells reverses insulin resistance and dysfunction of endothelial cells.

OBJECTIVE: Obese adipose tissue has been characterized with chronic inflammation associated with elevated secretion of inflammatory cytokines and declined secretion of anti-inflammatory cytokines which can impair endothelial function in an endocrine manner. Adipose tissue hypoxia plays a role in the changes of cytokines. Physical exercise/muscle contraction may help preventing cardiovascular disease through improving insulin resistance and endothelium function. However the mechanism is unclear. Skeletal muscle is an endocrine tissue. Contracting muscles secrete myokines which may play roles in the beneficial effect of exercise. In this study, the conditioned medium from electrical pulse stimulation (EPS) regulated skeletal muscle cells was used to explore the mechanism of contraction on endothelial dysfunction and insulin resistance induced by conditioned medium from hypoxic adipocytes.

METHODS: 3T3-L1 adipocytes were incubated under normoxia or hypoxia condition, respectively. The supernatant was collected as adipocyte conditioned medium (CM-N and CM-H). C2C12 mouse skeletal muscle cells were stimulated with EPS for 12 h. The supernatant was collected as muscle cells conditioned medium (CM-EPS). Human umbilical vein endothelial cells (HUVECs) were incubated with adipocyte CM and muscle cells CM together. Macrophages migration to HUVECs was detected with transwell system. The mRNA expressions of E-selectin, ICAM-1, MCP-1 and IL-6 were measured by real-time PCR. The phosphorylation of IKKα/β, NF-κB, Akt, AMPK, eNOS and SOCS3 protein levels were detected by Western blot. Concentration of NO was measured by ELISA kit. HUVECs apoptosis was detected by flow cytometry.

RESULTS: CM-EPS reduced the increase of mRNA expressions of E-selectin, ICAM-1, MCP-1 and IL-6 in HUVECs induced by CN-H. The phosphorylations of IKKα/β and NF-κB, SOCS3 protein level and endothelial cells apoptosis, which were raised by CM-H, were significantly reduced by CM-EPS. CM-EPS reversed the effects of CM-H on Akt and eNOS phosphorylations and NO production in HUVECs. CM-EPS directly stimulated the phosphorylation of AMPK, which caused the following phosphorylation of eNOS in HUVECs.

CONCLUSION: In summary, CM-EPS reversed endothelial cells inflammation, apoptosis, insulin resistance and dysfunction induced by CM-H.