Activation of spleen tyrosine kinase (SYK) contributes to neuronal pyroptosis and cognitive impairment in diabetic mice via the NLRP3/Caspase-1/GSDMD signaling pathway.

Diabetes mellitus (DM) patients are at increased risk of cognitive impairment. The precise mechanisms underlying the association between DM and cognitive impairment remain unclear. Spleen tyrosine kinase (SYK), a crucial regulator of signal transduction, has been implicated in microglial pyroptosis in experimental ischemic stroke models. The present study investigated the potential role of SYK in DM-associated cognitive impairment. Diabetes was induced by streptozotocin (STZ) in C57BL/6 mice, and cognitive function and cerebral injury were assessed 12 weeks later using the Morris water maze (MWM), TUNEL assay and Western blotting. In vitro, the inhibition of SYK was investigated in a mouse hippocampal neuronal cell line cultured with high glucose. Compared with control mice, DM mice presented impaired spatial learning and memory. Additionally, SYK activation was linked to neuronal pyroptosis, as evidenced by increases in the number of TUNEL-positive cells and protein levels of NLRP3, ASC, procaspase-1, caspase-1, GSDMD, the GSDMD N-terminal fragment, pro-IL-1β, and IL-1β in the hippocampus of DM mice. Compared with no treatment, SYK knockdown markedly attenuated cognitive impairment and histologic and ultrastructural pathological changes in the hippocampus of DM mice. The increased expression of pyroptosis-associated proteins and the increased number of TUNEL-positive cells were also significantly reduced. In vitro, high glucose significantly activated SYK to trigger the canonical pyroptotic pathway in cultured HT22 cells. The inhibition of SYK with a small interfering RNA or specific inhibitor significantly ameliorated the neuronal pyroptosis mediated by high glucose. Our findings demonstrate that SYK activation plays a pivotal role in promoting the cognitive impairment associated with DM. This effect is mediated by triggering neuronal pyroptosis through the canonical NLRP3/Caspase-1/GSDMD pathway. These results suggest that SYK may serve as a potential target for preventing or mitigating cognitive impairment in patients with DM.

Zhou C ，Li J ，Wu X ，Liu F ... -  《-》

Nerolidol rescues hippocampal injury of diabetic rats through inhibiting NLRP3 inflammasome and regulation of MAPK/AKT pathway.

Despite the observation of diabetes-induced brain tissue damage and impaired learning and memory, the underlying mechanism of damage remains elusive, and effective, targeted therapeutics are lacking. Notably, the NLRP3 inflammasome is highly expressed in the hippocampus of diabetic individuals. Nerolidol, a naturally occurring compound with anti-inflammatory and antioxidant properties, has been identified as a potential therapeutic option for metabolic disorders. However, the ameliorative capacity of nerolidol on diabetic hippocampal injury and its underlying mechanism remain unclear. Network pharmacology and molecular docking was used to predict the signaling pathways and therapeutic targets of nerolidol for the treatment of diabetes. Then established a diabetic rat model using streptozotocin (STZ) combined with a high-fat diet and nerolidol was administered. Morris water maze to assess spatial learning memory capacity. Hematoxylin and eosin and Nissl staining was used to detect neuronal damage in the diabetic hippocampus. Transmission electron microscopy was used to detect the extent of damage to mitochondria, endoplasmic reticulum (ER) and synapses. Immunofluorescence was used to detect GFAP, IBA1, and NLRP3 expression in the hippocampus. Western blot was used to detect apoptosis (Bcl-2, BAX, and Cleaved-Caspase-3); synapses (postsynaptic densifying protein 95, SYN1, and Synaptophysin); mitochondria (DRP1, OPA1, MFN1, and MFN2); ER (GRP78, ATF6, CHOP, and caspase-12); NLRP3 inflammasome (NLRP3, ASC, and caspase-1); inflammatory cytokines (IL-18, IL-1β, and TNF-α); AKT (P-AKT); and mitogen-activated protein kinase (MAPK) pathway (P-ERK, P-p38, and P-JNK) related protein expression. Network pharmacology showed that nerolidol's possible mechanisms for treating diabetes are the MAPK/AKT pathway and anti-inflammatory effects. Animal experiments demonstrated that nerolidol could improve blood glucose, blood lipids, and hippocampal neuronal damage in diabetic rats. Furthermore, nerolidol could improve synaptic, mitochondrial, and ER damage in the hippocampal ultrastructure of diabetic rats by potentially affecting synaptic, mitochondrial, and ER-related proteins. Further studies revealed that nerolidol decreased neuroinflammation, NLRP3 and inflammatory factor expression in hippocampal tissue while also decreasing MAPK pathway expression and enhancing AKT pathway expression. However, nerolidol improves hippocampal damage in diabetic rats cannot be shown to improve cognitive function. In conclusion, our study reveals for the first time that nerolidol can ameliorate hippocampal damage, neuroinflammation, synaptic, ER, and mitochondrial damage in diabetic rats. Furthermore, we suggest that nerolidol may inhibit NLRP3 inflammasome and affected the expression of MAPK and AKT. These findings provide a new experimental basis for the use of nerolidol to ameliorate diabetes-induced brain tissue damage and the associated disease.

Lei Y ，Li M ，Liu X ，Zhang L ，Zhang R ，Cai F ... -  《-》

Huang-Lian-Jie-Du decoction alleviates cognitive impairment in high-fat diet-induced obese mice via Trem2/Dap12/Syk pathway.

Cognitive impairment induced by a high-fat diet (HFD) is common, but its mechanism is largely unknown. Huang-Lian-Jie-Du (HLJD) decoction is a classical and powerful prescription in China. It consists of four medicinal plants and is widely used in traditional Chinese medicines (TCM). Studies have shown that HLJD decoction is effective in treating obesity, depression, and so on. However, the therapeutic mechanism of HLJD is still poorly understood. Our study aimed to explore whether inflammatory factors and Trem2/Dap12/Syk pathway are involved in this process and whether HLJD treatment can repair cognitive impairment in HFD-induced obesity. To obtain the obese mice, male mice were treated with HFD (60 Kcal% fat) for 16 weeks. After an additional eight weeks, HLJD decoction was administered orally at doses of 4 and 8 g/kg daily for eight weeks. The mice were then subjected to four behavior tests. Aβ42, total Tau, inflammatory-related, and microglial dysregulation-related markers expression were measured. Molecular docking analysis was also conducted to predict the interaction of the chemical constituents of HLJD with human TREM2, DAP12, and SYK. HLJD at doses of 12.5, 25, and 50 µg/mL or limonin at concentrations of 12.5, 25, and 50 µM were used to treat BV2 cells for 24 h. CCK8 assay and Trem2, Dap12, Syk, and p-Syk expression were measured. Our study revealed that cognitive impairment was evident in mice treated with HFD, indicating the impact of obesity on cognitive function. The expression of Aβ42 and total Tau in the hippocampus (HIP) was significantly higher in obese (HFD-V) mice compared to normal control (NC-V) mice. The Il6, Il1b, and Il10 mRNA expression levels were also markedly increased in the HIP of obese mice. Furthermore, Trem2, Dap12, p-Syk, and Iba1 expression were elevated in the HIP of obese mice. Importantly, HLJD treatment was found to repair cognitive impairment and lower the protein expression of Aβ42, Tau, Trem2, Dap12, p-Syk, and the expression of Il6, Il1b, and Il10 mRNA in HIP of HFD-V mice. The increased expression of Trem2, Dap12, p-Syk, and Iba1 in HIP after HFD consumption could be reduced after receiving HLJD decoction. The compound Limonin showed a well-predicted binding energy with TREM2, DAP12, and SYK. BV2 cells with HLJD or limonin detected the mRNA expressions of Trem2/Dap12. HLJD at 25 and 50 µg/mL decreased Trem2, Dap12, and p-Syk protein levels in BV2 cells. These results reveal that HLJD treatment could alleviate cognitive impairment in HFD-induced obese mice by controlling the activation of the Trem2/Dap12 pathway and reducing Syk phosphorylation in HIP microglia. HLJD and limonin suppressed Trem2/Dap12/Syk signaling pathway in BV2 cells. HLJD therapy might represent a novel treatment for patients with cognitive impairment induced by obesity.

Zheng JY ，Pang RK ，Ye JH ，Su S ，Shi J ，Qiu YH ，Pan HF ，Zheng RY ，Hu XR ，Deng QW ，Li XX ，Cai YF ，Zhang SJ ... -  《-》

The Stimulator of Interferon Genes Deficiency Attenuates Diabetic Myopathy Through Inhibiting NLRP3-Mediated Pyroptosis.

Diabetic myopathy is characterized by the loss of skeletal muscle mass and function. NOD-like receptor family pyrin domain containing 3 (NLRP3)-mediated pyroptosis is a type of proinflammatory cell death, which can exacerbate significant muscle cell loss and adverse remodelling. The stimulator of interferon genes (STING) is an essential molecule involved in the regulation of inflammation and immune responses across various diseases. The regulatory mechanism by which STING affects muscle pyroptosis in diabetic myopathy remains unclear. STING-knockout and wild-type (WT) mice underwent intraperitoneal injection of streptozotocin (STZ). STING small interfering RNA (siRNA) was transfected into fully differentiated C2C12 myotubes prior to glucose treatment. Muscle function tests, body composition analysis, transmission electron microscopy, scanning electron microscopy, western blotting, immunofluorescence, immunohistochemistry, histology, enzyme-linked immunosorbent assay, and reverse transcription polymerase chain reaction were performed. Co-immunoprecipitation assays were employed to investigate the interaction between STING and NLRP3. STING expression was elevated in the gastrocnemius muscle (GM) tissues of WT diabetic mice. STING-deficient diabetic mice exhibited pronounced hyperglycaemia accompanied by hypoinsulinaemia, with no significant difference compared with WT diabetic mice. However, STING-deficient diabetic mice demonstrated a significantly increased body weight and lean mass. A significant decrease in muscle weight, myofibrillar diameter and area, muscle function, and the expression of genes related to muscle atrophy (MuRF1, Atrogin1) were observed in WT diabetic mice, which was mitigated in STING-deficient diabetic mice. STING deficiency reduced the number of GSDMD-N formed pores and pyroptosis-related components (NLRP3, caspase-1, cle-caspase-1, GSDMD, and GSDMD-N) in the GM tissues and was associated with a reduction in inflammatory chemokines. Similar changes were observed in vitro with glucose-induced myotube atrophy and pyroptosis as seen in vivo. Activation of STING by the agonist diABZI exacerbated muscle atrophy and pyroptosis in C2C12 myotubes. Co-localization of STING and NLRP3 was observed, and the interaction between STING and NLRP3 was enhanced in GM tissues from WT diabetic mice. We also found that STING could activate NLRP3 dependent on its channel activity, which can be attenuated by treated with C53 (an inhibitor of STING's ion-channel function). In conclusion, our results indicate that STING-induced activation of the NLRP3 inflammasome leads to pyroptosis, resulting in muscle atrophy and dysfunction. These findings not only elucidate the mechanism of STING-induced pyroptosis but also identify STING as a potential therapeutic target for diabetic myopathy.

Yang J ，Wang M ，Shi L ，Fang X ，Gao C ，Ma L ，Wang Y ，Ying S ，Yang Y ... -  《-》

TFEB signaling promotes autophagic degradation of NLRP3 to attenuate neuroinflammation in diabetic encephalopathy.

Lin Y ，Cheng L ，Chen Y ，Li W ，Guo Q ，Miao Y ... -  《-》