Insulin signaling pathway in the masseter muscle of dexamethasone-treated rats

Masseter muscle and gingival tissue inflammatory response following treatment with high-fructose corn syrup in rats: Anti-inflammatory and antioxidant effects of kefir

The aim of the study was to evaluate whether high-fructose corn syrup (HFCS) intake (20% beverages) impacts antioxidative structures and inflammation in the gingival tissue and masseter muscle of rats. Kefir was tested for its potential utility on changes induced by HFCS. Animals were randomly divided into four groups as control, kefir, HFCS, and HFCS plus kefir. HFCS was given as 20% solutions in drinking water while kefir supplementations were given by gastric gavage for 8 weeks. It has been clearly determined that the HFCS diet increased expressions of interleukin (IL)-6, IL-1β, and tumor necrosis factor-α proinflammatory structures via lymphocyte infiltration by suppressing antioxidant enzymes such as catalase, superoxide dismutase, and glutathione peroxidase in both tissues. Kefir improved these undesirable changes in rats fed with HFCS. The results of this current study, the first investigation to examine the effects of kefir on masseter muscle and gingival tissue, may provide new access to the restorative effects of kefir consumption on oral health disorders caused by high fructose in the diet. PRACTICAL APPLICATIONS: In this study, at an early age, the effects of kefir on improving inflammation via antioxidation in the masseter muscle and gingival tissue were investigated for the first time. We showed that kefir feeding ameliorates lymphocyte infiltration on the high-fructose corn syrup (HFCS)-induced masseter muscle and gingival tissue inflammation in rats. The mRNA expressions of inflammatory parameters measured in the study were supported by protein measurements via ELISA or immunohistochemistry. In the present study, kefir may play an important role in the antioxidation and inflammation process on the masseter muscle and gingival tissue against HFCS.

The steroid hormone 20-hydroxyecdysone counteracts insulin signaling via insulin receptor dephosphorylation

The insulin receptor (INSR) binds insulin to promote body growth and maintain normal blood glucose levels. While it is known that steroid hormones such as estrogen and 20-hydroxyecdysone counteract insulin function, the molecular mechanisms responsible for this attenuation remain unclear. In the present study, using the agricultural pest lepidopteran Helicoverpa armigera as a model, we proposed that the steroid hormone 20-hydroxyecdysone (20E) induces dephosphorylation of INSR to counteract insulin function. We observed high expression and phosphorylation of INSR during larval feeding stages that decreased during metamorphosis. Insulin upregulated INSR expression and phosphorylation, whereas 20E repressed INSR expression and induced INSR dephosphorylation in vivo. Protein tyrosine phosphatase 1B (PTP1B, encoded by Ptpn1) dephosphorylated INSR in vivo. PTEN (phosphatase and tensin homolog deleted on chromosome 10) was critical for 20E-induced INSR dephosphorylation by maintaining the transcription factor Forkhead box O (FoxO) in the nucleus, where FoxO promoted Ptpn1 expression and repressed Insr expression. Knockdown of Ptpn1 using RNA interference maintained INSR phosphorylation, increased 20E production, and accelerated pupation. RNA interference of Insr in larvae repressed larval growth, decreased 20E production, delayed pupation, and accumulated hemolymph glucose levels. Taken together, these results suggest that a high 20E titer counteracts the insulin pathway by dephosphorylating INSR to stop larval growth and accumulate glucose in the hemolymph.