Retinoic Acid Receptor Gamma (RARγ) Promotes Cartilage Destruction through Positive Feedback Activation of NF-κB Pathway in Human Osteoarthritis.

Osteoarthritis (OA) is a severe inflammation-related disease which leads to cartilage destruction. The retinoic acid receptor gamma (RARγ) has been indicated to be involved in many inflammation processes. However, the role and mechanism of RARγ in cartilage destruction caused by inflammation in OA are still unknown. Here, we demonstrated that the RARγ was highly expressed in chondrocytes of OA patients compared with healthy people and was positively correlated with the damage degree of cartilage in OA. Cytokine TNF-α promoted the transcription and expression of RARγ through activating the NF-κB pathway in OA cartilage. In addition, the overexpression of RARγ resulted in the upregulation of matrix degradation and inflammation associated genes and downregulation of differentiation and collagen production genes in human normal chondrocyte C28/I2 cells. Mechanistically, overexpression of RARγ could increase the level of p-IκBα and p-P65 to regulate the expression of downstream genes. RARγ and IκBα also could interact with each other and had the same localization in C28/I2 cells. Moreover, the SD rats OA model induced by monosodium iodoacetate indicated that CD437 (RARγ agonist) and TNF-α accelerated the OA progression, including more severe cartilage layer destruction, larger knee joint diameter, and higher serum ALP levels, while LY2955303 (RARγ inhibitor) showed the opposite result. RARγ was also highly expressed in OA group and even higher in TNF-α group. In conclusion, RARγ/NF-κB positive feedback loop was activated by TNF-α in chondrocyte to promote cartilage destruction. Our data not only propose a novel and precise molecular mechanism for OA disease but also provide a prospective strategy for the treatment.

Osteopontin deficiency protects mice from cholesterol gallstone formation by reducing expression of intestinal NPC1L1.

Homeostasis of cholesterol is regulated by absorption in the intestine and synthesis in the liver. The authors previously demonstrated that OPN (osteopontin) exhibits the ability to alter hepatic cholesterol metabolism, thus affecting cholesterol gallstone formation in mice. The present study investigated the role of OPN in cholesterol gallstone formation, focusing on its effect on intestinal absorption of cholesterol. OPN gene knockout (OPN­/­) mice and wild­type mice were respectively fed with a chow or lithogenic diet (LD) for 8 weeks. Following an 8­week LD period, the incidence of gallstone, bile composition, level of serum and fecal lipids and the expression of intestinal associated genes were analyzed. OPN­/­ mice were protected from gallstone formation induced by 8 weeks' LD­feeding. This protective effect from OPN deficiency was associated with alterations in bile composition, including a reduced concentration of biliary cholesterol. Additionally, plasma cholesterol level was decreased in LD­fed OPN­/­ mice. The alterations primarily resulted from the decreased expression of intestinal Niemann­Pick C1­like (NPC1 L) 1, which is important in the intestinal absorption of cholesterol. The present study demonstrated that OPN deficiency reduced intestinal absorption of cholesterol by suppressing the expression of NPC1L1, thus protecting mice from cholesterol gallstone formation.

Ischemic post-conditioning attenuates renal ischemic reperfusion injury via down-regulation of toll-like receptor 4 in diabetic rats.

BACKGROUND: Ischemia/reperfusion (I/R) injury, which is commonly seen in the field of renal surgery or transplantation, is a major cause of acute renal failure (ARF). The ischemic ARF in diabetic rats is much more severe than that in the normal rats exposed to as same ischemic time. Ischemic post-conditioning (IPO) is a phenomenon by which intermittent interruptions of blood flow in the early phase of reperfusion can protect organs from I/R injury. To determine whether the renal protection effect of IPO mediates by toll-like receptor 4 (TLR4) signaling pathway in diabetic rats. METHODS: Streptozotocin-induced diabetic rats were randomly divided into three groups: sham operation group, I/R group, and IPO group. Except sham operation group, rats were subjected to 30 min of renal ischemia, both with and without treatment with IPO, then reperfusion 24 h. Light microscope and transmission electronic microscope were used to observe structural changes of renal tubule. RT-PCR was used to measure TLR4 and tumor necrosis factor-alpha (TNF-α) mRNA expression level, renal TLR4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) protein expression was detected by Western blot. RESULTS: The results demonstrated that IPO markedly decreased renal ischemic injury caused by I/R and inhibited the proinflammatory expression levels of TLR4, TNF-α, and NF-κB, all of which up-regulated by I/R in diabetic rats. CONCLUSION: Taken together, our results suggest that proper IPO may have protective effect on the ischemic injury mediated by renal I/R, which might be associated with inhibition of TLR4 signaling pathway in diabetic rats.