Nutritional abundance associated with chronic inflammation and dyslipidemia impairs the functioning of endoplasmic reticulum (ER) thereby hampering cellular responses to insulin. PHLPP1 was identified as a phosphatase which inactivates Akt, the master regulator of insulin mediated glucose homeostasis. Given the suggestive role of PHLPP1 phosphatase in terminating insulin signalling pathways, deeper insights into its functional role in inducing insulin resistance are warranted. Here, we show that PHLPP1 expression is enhanced in skeletal muscle of insulin resistant rodents which also displayed ER stress, an important mediator of insulin resistance. Using cultured cells and PHLPP1 knockdown mice, we demonstrate that PHLPP1 facilitates the development of ER stress. Importantly, shRNA mediated ablation of PHLPP1 significantly improved glucose clearance from systemic circulation with enhanced expression of glucose transporter 4 (GLUT-4) in skeletal muscle. Mechanistically, we show that endogenous PHLPP1 but not PP2Cα interacts with and directly dephosphorylates AMPK Thr in myoblasts without influencing its upstream kinase, LKB1. While the association between endogenous PHLPP1 and AMPK was enhanced in ER stressed cultured cells and soleus muscle of high fat diet fed mice, the basal interaction between PP2Ac and AMPK was minimally altered. Further, we show that PHLPP1α is phosphorylated by ERK1/2 at Ser under ER stress which is required for its ability to interact with and dephosphorylate AMPK and thereby induce ER stress. Taken together, our data position PHLPP1 as a key regulator of ER stress.

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The present study was undertaken to investigate the anti-inflammatory effect of piperine against adjuvant-induced arthritis in rats, an experimental model for rheumatoid arthritis and compared it with that of the non-steroidal anti-inflammatory drug indomethacin. Administration of heat-killed Mycobacterium tuberculosis (0. 1 ml) intradermally into the right hind paw of rats resulted in increased paw volume, lysosomal enzymes, glycoproteins and tissue marker enzymes and decreased body weight. However, these changes were reverted to near normal levels upon piperine (30 mg/kg body weight, i.p.) treatment. Histopathological analysis of joints also revealed that synovial hyperplasia and mononuclear infiltration observed in arthritic rats were alleviated by piperine. Thus, the present study clearly indicated that piperine possesses promising anti-inflammatory effect against adjuvant-induced arthritis by suppressing inflammation and cartilage destruction.

p-Coumaric acid (3-(4-hydroxyphenyl)-2-propenoic acid), a common dietary polyphenol, is widely distributed in cereals, fruits and vegetables with antioxidant property. Numerous studies have enlightened the ability of dietary phenols to be considered as potential therapeutics against arthritis. In this study, we aimed to investigate the ameliorative effect of plant phenolic p-coumaric acid on adjuvant-induced arthritis in rats. The reference drug indomethacin was used for comparison purposes. Arthritis was induced in rats by a single intradermal injection of complete freund's adjuvant (0.1 mL) into the foot pad of right hind paw. p-Coumaric acid (100 mg/kg b wt) and indomethacin (3 mg/kg b wt) were administered intraperitoneally for 8 days from day 11 to 18 after adjuvant injection. An increase in the activities/levels of lysosomal enzymes, tissue marker enzymes, glycoproteins and paw thickness was observed in the arthritic rats, on the contrary, the body weight was found to be reduced in arthritic rats when compared to normal control rats. Administration of p-coumaric acid (100 mg/kg b wt) to the arthritic rats reverted back the altered physical and biochemical parameters to near normal levels comparable to indomethacin treatment. Histopathological evaluation of ankle joints in arthritic rats also revealed the anti-inflammatory effect of p-coumaric acid by the reduction in leukocytes infiltration. Thus, the present study clearly demonstrates the anti-inflammatory potential of the p-coumaric acid against adjuvant-induced arthritis in rats.