TNF-α Suppresses Apelin Receptor Expression in Mouse Quadriceps Femoris-Derived Cells

Expression of the apelin receptor, APJ, in skeletal muscle (SM) is known to decrease with age, but the underlying mechanism remains unclear. Increased tumor necrosis factor (TNF)-alpha levels are observed in SM with age and are associated with muscle atrophy. To investigate the possible interconnection between TNF-alpha elevation and APJ reduction with aging, we investigated the effect of TNF-alpha on APJ expression in cells derived from the quadriceps femoris of C57BL/6J mice. Expression of Tnfa and Apj in the quadriceps femoris was compared between 4- (young) and 24-month-old (old) C57BL/6J mice (n = 10 each) using qPCR. Additionally, APJ-positive cells and TNF-alpha protein were analyzed by flow cytometry and Western blotting, respectively. Further, quadricep-derived cells were exposed to 0 (control) or 25 ng/mL TNF-alpha, and the effect on Apj expression was examined by qRT-PCR. Apj expression and the ratio of APJ-positive cells among quadricep cells were significantly lower in old compared to young mice. In contrast, levels of Tnfa mRNA and TNF-alpha protein were significantly elevated in old compared to young mice. Exposing young and old derived quadricep cells to TNF-alpha for 8 and 24 h caused Apj levels to significantly decrease. TNF-alpha suppresses APJ expression in muscle cells in vitro. The increase in TNF-alpha observed in SM with age may induce a decrease in APJ expression.

Automated summary

The expression of APJ in skeletal muscle decreases with age, possibly due to the elevated levels of TNF-alpha observed in older individuals. TNF-alpha can suppress the expression of APJ in muscle cells in vitro, indicating a potential interconnection between TNF-alpha elevation and APJ reduction in aging.