General anesthetic actions on GABAA receptors in vivo are reduced in phospholipase C-related catalytically inactive protein knockout mice.

PURPOSE: The aim of this study was to investigate the action of general anesthetics in phospholipase C-related catalytically inactive protein (PRIP)-knockout (KO) mice that alter GABAA receptor signaling. METHODS: PRIP regulates the intracellular trafficking of ß subunit-containing GABAA receptors in vitro. In this study, we examined the effects of intravenous anesthetics, propofol and etomidate that act via ß subunit-containing GABAA receptors, in wild-type and Prip-KO mice. Mice were intraperitoneally injected with a drug, and a loss of righting reflex (LORR) assay and an electroencephalogram analysis were performed. RESULTS: The cell surface expression of GABAA receptor ß3 subunit detected by immunoblotting was decreased in Prip-knockout brain compared with that in wild-type brain without changing the expression of other GABAA receptor subunits. Propofol-treated Prip-KO mice exhibited significantly shorter duration of LORR and had lower total anesthetic score than wild-type mice in the LORR assay. The average duration of sleep time in an electroencephalogram analysis was shorter in propofol-treated Prip-KO mice than in wild-type mice. The hypnotic action of etomidate was also reduced in Prip-KO mice. However, ketamine, an NMDA receptor antagonist, had similar effects in the two genotypes. CONCLUSION: PRIP regulates the cell surface expression of the GABAA receptor ß3 subunit and modulates general anesthetic action in vivo. Elucidation of the involved regulatory mechanisms of GABAA receptor-dependent signaling would inform the development of safer anesthetic therapies for clinical applications.

Phospholipase C-related Catalytically Inactive Protein Is a New Modulator of Thermogenesis Promoted by ß-Adrenergic Receptors in Brown Adipocytes.

Phospholipase C-related catalytically inactive protein (PRIP) was first identified as an inositol 1,4,5-trisphosphate-binding protein, and was later found to be involved in a variety of cellular events, particularly those related to protein phosphatases. We previously reported that Prip knock-out (KO) mice exhibit a lean phenotype with a small amount of white adipose tissue. In the present study, we examined whether PRIP is involved in energy metabolism, which could explain the lean phenotype, using high-fat diet (HFD)-fed mice. Prip-KO mice showed resistance to HFD-induced obesity, resulting in protection from glucose metabolism dysfunction and insulin resistance. Energy expenditure and body temperature at night were significantly higher in Prip-KO mice than in wild-type mice. Gene and protein expression of uncoupling protein 1 (UCP1), a thermogenic protein, was up-regulated in Prip-KO brown adipocytes in thermoneutral or cold environments. These phenotypes were caused by the promotion of lipolysis in Prip-KO brown adipocytes, which is triggered by up-regulation of phosphorylation of the lipolysis-related proteins hormone-sensitive lipase and perilipin, followed by activation of UCP1 and/or up-regulation of thermogenesis-related genes (e.g. peroxisome proliferator-activated receptor-γ coactivator-1α). The results indicate that PRIP negatively regulates UCP1-mediated thermogenesis in brown adipocytes.

Phospholipase C-related catalytically inactive protein (PRIP) regulates lipolysis in adipose tissue by modulating the phosphorylation of hormone-sensitive lipase.

Phosphorylation of hormone-sensitive lipase (HSL) and perilipin by protein kinase A (PKA) promotes the hydrolysis of lipids in adipocytes. Although activation of lipolysis by PKA has been well studied, inactivation via protein phosphatases is poorly understood. Here, we investigated whether phospholipase C-related catalytically inactive protein (PRIP), a binding partner for protein phosphatase 1 and protein phosphatase 2A (PP2A), is involved in lipolysis by regulating phosphatase activity. PRIP knockout (PRIP-KO) mice displayed reduced body-fat mass as compared with wild-type mice fed with standard chow ad libitum. Most other organs appeared normal, suggesting that mutant mice had aberrant fat metabolism in adipocytes. HSL in PRIP-KO adipose tissue was highly phosphorylated compared to that in wild-type mice. Starvation of wild-type mice or stimulation of adipose tissue explants with the catabolic hormone, adrenaline, translocated both PRIP and PP2A from the cytosol to lipid droplets, but the translocation of PP2A was significantly reduced in PRIP-KO adipocytes. Consistently, the phosphatase activity associated with lipid droplet fraction in PRIP-KO adipocytes was significantly reduced and was independent of adrenaline stimulation. Lipolysis activity, as assessed by measurement of non-esterified fatty acids and glycerol, was higher in PRIP-KO adipocytes. When wild-type adipocytes were treated with a phosphatase inhibitor, they showed a high lipolysis activity at the similar level to PRIP-KO adipocytes. Collectively, these results suggest that PRIP promotes the translocation of phosphatases to lipid droplets to trigger the dephosphorylation of HSL and perilipin A, thus reducing PKA-mediated lipolysis.