Insulin, dibutyryl-cAMP, and glucose modulate expression of patatin-like domain containing protein 7 in cultured human myotubes

Abstract

Expression of patatin-like phospholipase domain containing protein 7 (PNPLA7), also known as neuropathy target esterase-related esterase (NRE), a lysophospholipase, increases with fasting and decreases with feeding in mouse skeletal muscle, indicating it is regulated by insulin, counterregulatory hormones, such as glucocorticoids and catecholamines, and/or nutrients. In cultured mouse adipocytes insulin reduces Pnpla7 expression, underscoring the possibility that insulin regulates PNPLA7 in skeletal muscle. The first aim of this study was to establish whether PNPLA7 is functionally expressed in cultured human skeletal muscle cells. The second aim was to determine whether PNPLA7 is regulated by insulin, glucocorticoids, cAMP/protein kinase A pathway, and/or glucose. Cultured human skeletal muscle cells expressed PNPLA7 mRNA and protein. Gene silencing of PNPLA7 in myoblasts reduced the phosphorylation of 70 kDa ribosomal protein S6 kinase and ribosomal protein S6 as well as the abundance of α1-subunit of Na+,K+-ATPase and acetyl-CoA carboxylase, indirectly suggesting that PNPLA7 is functionally important. In myotubes, insulin suppressed PNPLA7 mRNA at 1 g/L glucose, but not at low (0.5 g/L) or high (4.5 g/L) concentrations. Treatment with synthetic glucocorticoid dexamethasone and activator of adenylyl cyclase forskolin had no effect on PNPLA7 regardless of glucose concentration, while dibutyryl-cAMP, a cell-permeable cAMP analogue, suppressed PNPLA7 mRNA at 4.5 g/L glucose. The abundance of PNPLA7 protein correlated inversely with the glucose concentrations. Collectively, our results highlight that PNPLA7 in human myotubes is regulated by metabolic signals, implicating a role for PNPLA7 in skeletal muscle energy metabolism.

The PNPLA family of enzymes: characterisation and biological role

“…In one of our studies (100), we found that knocking down the mRNA of PNPLA7 in cultured human myoblasts significantly reduces the α1-subunit of Na + K + -ATPase, acetyl-CoA carboxylase, phosphorylated forms of the 70 kDa ribosomal S6 kinase, and ribosomal protein S6, which suggests that PNPLA7 is important for the function of human myoblasts in a number of aspects (100). Several studies (101−103) in which PNPLA7 was knocked down have confirmed the biological importance of PNPLA7 in energy metabolism and its role in the development of metabolic disorders.…”

“…Furthermore, it is suppressed by insulin in the 3T3-L1 adipocytes. A recent study with cultured human myotubes ( 100 ) has shown that insulin suppresses mRNA expression in physiological conditions and dibutyryl-cAMP in the fed state and that PNPLA7 protein levels inversely correlate with glucose concentrations. All this suggests that PNPLA7 is regulated by the nutritional status and plays a role in energy metabolism.…”

Electrical stimulation of the diaphragm may counteract muscle degradation during prolonged mechanical ventilation: A pilot study using transcriptome analyses

“…Of note, among the genes associated with three enriched GO terms related to catabolic processes, Pnpla2, Samd4b, Tmem259, and Pcbp4 were upregulated by 12-hour MV and downregulated by ES. Pnpla7, the gene whose expression was most altered by 12-hour MV, regulates skeletal muscle energy metabolism by inversely correlating with insulin 33 . Therefore, ES might counteract the catabolic process caused by 12-hour MV.…”