Trigeminal neuralgia (TN) is a type of severe paroxysmal neuropathic pain commonly triggered by mild mechanical stimulation in the orofacial area. Piezo2, a mechanically gated ion channel that mediates tactile allodynia in neuropathic pain, can be potentiated by a cyclic adenosine monophosphate (cAMP)-dependent signaling pathway that involves the exchange protein directly activated by cAMP 1 (Epac1). To study whether Piezo2-mediated mechanotransduction contributes to peripheral sensitization in a rat model of TN after trigeminal nerve compression injury, the expression of Piezo2 and activation of cAMP signal-related molecules in the trigeminal ganglion (TG) were detected. Changes in purinergic P2 receptors in the TG were also studied by RNA-seq. The expression of Piezo2, cAMP, and Epac1 in the TG of the TN animals increased after chronic compression of the trigeminal nerve root (CCT) for 21 days, but Piezo2 knockdown by shRNA in the TG attenuated orofacial mechanical allodynia. Purinergic P2 receptors P2X4, P2X7, P2Y1, and P2Y2 were significantly up-regulated after CCT injury. In vitro, Piezo2 expression in TG neurons was significantly increased by exogenous adenosine 5'-triphosphate (ATP) and Ca 2+ ionophore ionomycin. ATP pre-treated TG neurons displayed elevated [Ca 2+ ] i and faster increase in responding to blockage of Na + /Ca 2+ exchanger by KB-R7943. Furthermore, mechanical stimulation of cultured TG neurons led to sustained elevation in [Ca 2+ ] i in ATP pre-treated TG neurons, which is much less in naïve TG neurons, or is significantly reduced by Piezo2 inhibitor GsMTx4. These results indicated a pivotal role of Piezo2 in peripheral mechanical allodynia in the rat CCT model. Extracellular ATP, Ca 2+ influx, and the cAMP-to-Epac1 signaling pathway synergistically contribute to the pathogenesis and the persistence of mechanical allodynia.

Background: Inulin is a natural plant extract that improves metabolic syndrome by modulating the gut microbiota. Changes in the gut microbiota may affect intestinal bile acids. We suggest that inulin may improve metabolism by inducing bile acid excretion by gut microbes.Methods: Male C57/BL mice were fed either a high-fat diet (60% calories) or a regular diet for 16 weeks, with oral inulin (10% w/w). At the end of the experiment, the gene expression levels (FGF15, CD36, Srebp-1c, FASN, and ACC) in the liver and intestines, as well as the serum levels of triglycerides (TGs), low-density lipoprotein (LDL) cholesterol, total cholesterol, and free fatty acids, were collected. The expression of FGF15 was examined using Western blot analysis. The fat distribution in the liver and groin was detected by oil red and hematoxylin and eosin staining. Simultaneously, the levels of serum inflammatory factors (alanine aminotransferase and aspartate aminotransferase) were detected to explore the side effects of inulin.Results: Inulin significantly improved glucose tolerance and insulin sensitivity, and decreased body weight and serum TG and LDL levels, in mice fed normal diet. Furthermore, inulin increased the α-diversity of the gut microbiota and increased the fecal bile acid and TG excretion in inulin-treated mice. In addition, inulin significantly reduced lipid accumulation in liver and inguinal fat, white fat weight, and hepatic steatosis. Western blot analysis showed that inulin reduced the expression of FGF15, a bile acid reabsorption protein.Conclusion: Inulin ameliorates the glucose and lipid metabolic phenotypes of mice fed a normal diet, including decreased intestinal lipid absorption, increased glucose tolerance, increased insulin sensitivity, and decreased body weight. These changes may be caused by an increase in bile acid excretion resulting from changes in the gut microbiota that affect intestinal lipid absorption.