MD2 deficiency prevents high-fat diet-induced AMPK suppression and lipid accumulation through regulating TBK1 in non-alcoholic fatty liver disease

Extract of Silphium perfoliatum L. improve lipid accumulation in NAFLD mice by regulating AMPK/FXR signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Globally, the incidence rate and number of patients with nonalcoholic fatty liver disease are increasing, which has become one of the greatest threats to human health. However, there is still no effective therapy and medicine so far. Silphium perfoliatum L. is a perennial herb native to North America, which is used to improve physical fitness and treat liver and spleen related diseases in the traditional medicinal herbs of Indian tribes. This herb is rich in chlorogenic acids, which have the functions of reducing blood lipids, losing weight and protecting liver. However, the effect of these compounds on nonalcoholic fatty liver disease remains unclear.

AIM OF THE STUDY

Clarify the therapeutic effects and mechanism of the extract (CY-10) rich in chlorogenic acid and its analogues from Silphium perfoliatum L. on non-alcoholic fatty liver disease, and to determine the active compounds.

MATERIALS AND METHODS

A free fatty acid-induced steatosis model of HepG2 cells was established to evaluate the in vitro activity of CY-10 in promoting lipid metabolism. Further, a high-fat diet-induced NAFLD model in C57BL/6 mice was established to detect the effects of CY-10 on various physiological and biochemical indexes in mice, and to elucidate the in vivo effects of the extract on regulating lipid metabolism, anti-inflammation and hepatoprotection, and nontarget lipid metabolomics was performed to analyze differential metabolites of fatty acids in the liver. Subsequently, western blotting and immunohistochemistry were used to analyze the target of the extract and elucidate its mechanism of action. Finally, the active compounds in CY-10 were elucidated through in vitro activity screening.

RESULTS

The results indicated that CY-10 significantly attenuated lipid droplet deposition in HepG2 cells. The results of in vivo experiments showed that CY-10 significantly reduce HFD-induced mouse body weight and organ index, improve biochemical indexes, oxidation levels and inflammatory responses in the liver and serum, thereby protecting the liver tissue. It can promote the metabolism of unsaturated fatty acids in the liver and reduce the generation of saturated fatty acids. Furthermore, it is clarified that CY-10 can promote lipid metabolism balance by regulating AMPK/FXR/SREPB-1c/PPAR-γ signal pathway. Ultimately, the main active compound was proved to be cryptochlorogenic acid, which has a strong promoting effect on the metabolism of fatty acids in cells. Impressively, the activities of CY-10 and cryptochlorogenic acid were stronger than simvastatin in vitro and in vivo.

CONCLUSION

For the first time, it is clarified that the extract rich in chlorogenic acids and its analogues in Silphium perfoliatum L. have good therapeutic effects on non-alcoholic fatty liver disease. It is confirmed that cryptochlorogenic acid is the main active compound and has good potential for medicine.

The cGAS-STING pathway: a therapeutic target in diabetes and its complications

Diabetic wound healing (DWH) represents a major complication of diabetes where inflammation is a key impediment to proper healing. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a central mediator of inflammatory responses to cell stress and damage. However, the contribution of cGAS-STING activation to impaired healing in DWH remains understudied. In this review, we examine the evidence that cGAS-STING-driven inflammation is a critical factor underlying defective DWH. We summarize studies revealing upregulation of the cGAS-STING pathway in diabetic wounds and discuss how this exacerbates inflammation and senescence and disrupts cellular metabolism to block healing. Partial pharmaceutical inhibition of cGAS-STING has shown promise in damping inflammation and improving DWH in preclinical models. We highlight key knowledge gaps regarding cGAS-STING in DWH, including its relationships with endoplasmic reticulum stress and metal-ion signaling. Elucidating these mechanisms may unveil new therapeutic targets within the cGAS-STING pathway to improve healing outcomes in DWH. This review synthesizes current understanding of how cGAS-STING activation contributes to DWH pathology and proposes future research directions to exploit modulation of this pathway for therapeutic benefit.

CARD9 deficiency aggravated nonalcoholic steatohepatitis in mice through increasing inflammatory response

Nonalcoholic steatohepatitis (NASH), a subtype of nonalcoholic fatty liver disease (NAFLD), is the leading cause of liver-related morbidity worldwide. Caspase recruitment domain family member 9 (CARD9), a myeloid cell-specific signaling protein, belongs to the CARD protein family. However, its role in NASH is unknown. Therefore, this study aimed to investigate the role of CARD9 in the development of NASH. NASH models were established using CARD9-knockout and wild-type mice. They were either fed a methionine/choline deficient (MCD) diet for 6 weeks or a high-fat high-cholesterol (HFHC) diet for 16 weeks. Liver fibrosis model was also developed using CCl4. CARD9 deficiency accelerated steatohepatitis development in MCD or HFHC diet-fed mice, accompanied by an upregulation of fibrosis, adipogenesis, and proinflammatory genes. CARD9 deficiency was found to exacerbate CCl4-induced liver fibrosis. In vitro studies demonstrated that CARD9 deficiency induced the expression of S100a8/a9 through Toll-like receptor in Kupffer cells treated with palmitate. This led to an increased expression of proinflammatory, fibrosis, and lipid metabolism-related genes in NASH progression. These results highlight the role of CARD9 in the development of NASH and provide new insights into the therapeutic strategies for NASH.

Inhibition of MD2 by natural product-drived JM-9 attenuates renal inflammation and diabetic nephropathy in mice

Diabetic kidney disease (DKD) is one of the severe complications of diabetes mellitus-related microvascular lesions, which remains the leading cause of end-stage kidney disease. The genesis and development of DKD is closely related to inflammation. Myeloid differentiation 2 (MD2) mediates hyperlyciemia-induced renal inflammation and DKD development and is considered as a potential therapeutic target of DKD. Here, we identified a new small-molecule MD2 inhibitor, JM-9. In vitro, JM-9 suppressed high glucose (HG) and palmitic acid (PA)-induced inflammation in MPMs, accompanied by inhibition of MD2 activation and the downstream TLR4/MyD88-MAPKs/NFκB pro-inflammatory signaling pathway. Macrophage-derived factors increased the fibrotic and inflammatory responses in renal tubular epithelial cells, which were inhibited by treating macrophages with JM-9. Then, we investigated the therapeutic effects against DKD in streptozotocin-induced type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) mouse models. Treatment with JM-9 prevented renal inflammation, fibrosis, and dysfunction by targeting MD2 in both T1DM and T2DM models. Our results show that JM-9, a new small-molecule MD2 inhibitor, protects against DKD by targeting MD2 and inhibiting MD2-mediated inflammation. In summary, JM-9 is a potential therapeutic agent for DKD.

Dectin-1 plays a deleterious role in high fat diet-induced NAFLD of mice through enhancing macrophage activation

The innate immune response and inflammation contribute to hepatic steatosis and non-alcoholic fatty liver disease (NAFLD). Dectin-1 is a pathogen recognition receptor in innate immunity. In this study, we investigated the role of Dectin-1 in the pathogenesis of NAFLD. We first showed that Dectin-1 expression was significantly elevated in liver tissues of patients with NASH. NAFLD was induced in mice by feeding high fat diet (HFD) for 24 weeks. At the end of treatment, mice were sacrificed, and their blood and liver tissues were collected for analyses. We showed HFD feeding also increased liver Dectin-1 levels in mice, associated with macrophage infiltration. Either gene knockout or co-administration of a Dectin-1 antagonist laminarin (150 mg/kg twice a day, ip, from 16^th week to 24^th week) largely protected the livers from HFD-induced lipid accumulation, fibrosis, and elaboration of inflammatory responses. In primary mouse peritoneal macrophages (MPMs), challenge with palmitate (PA, 200 μM), an abundant saturated fatty acid found in NAFLD, significantly activated Dectin-1 signaling pathway, followed by transcriptionally regulated production of pro-inflammatory cytokines. Dectin-1 was required for hepatic macrophage activation and inflammatory factor induction. Condition media generated from Dectin-1 deficient macrophages failed to cause hepatocyte lipid accumulation and hepatic stellate activation. In conclusion, this study provides the primary evidence supporting a deleterious role for Dectin-1 in NAFLD through enhancing macrophage pro-inflammatory responses and suggests that it can be targeted to prevent inflammatory NAFLD.

The AMPK pathway in fatty liver disease

Lipid metabolism disorders are the primary causes for the occurrence and progression of various liver diseases, including non-alcoholic fatty liver disease (NAFLD) and alcoholic fatty liver disease (AFLD) caused by a high-fat diet and ethanol. AMPK signaling pathway plays an important role in ameliorating lipid metabolism disorders. Progressive research has clarified that AMPK signal axes are involved in the prevention and reduction of liver injury. Upregulation of AMK can alleviate FLD in mice induced by alcohol or insulin resistance, type 2 diabetes, and obesity, and most natural AMPK agonists can regulate lipid metabolism, inflammation, and oxidative stress in hepatocytes, consequently regulating FLD in mice. In NAFLD and AFLD, increasing the activity of AMPK can inhibit the synthesis of fatty acids and cholesterol by down-regulating the expression of adipogenesis gene (FAS, SREBP-1c, ACC and HMGCR); Simultaneously, by increasing the expression of fatty acid oxidation and lipid decomposition genes (CPT1, PGC1, and HSL, ATGL) involved in fatty acid oxidation and lipid decomposition, the body’s natural lipid balance can be maintained. At present, some AMPK activators are thought to be beneficial during therapeutic treatment. Therefore, activation of AMPK signaling pathway is a potential therapeutic target for disorders of the liver. We summarized the most recent research on the role of the AMPK pathway in FLD in this review. Simultaneously, we performed a detailed description of each signaling axis of the AMPK pathway, as well as a discussion of its mechanism of action and therapeutic significance.