Neuroprotective effect of salidroside on hippocampal neurons in diabetic mice via PI3K/Akt/GSK-3ß signaling pathway.

BACKGROUND: Diabetic encephalopathy is manifested by cognitive dysfunction. Salidroside, a nature compound isolated from Rhodiola rosea L, has the effects of anti-inflammatory and antioxidant, hypoglycemic and lipid-lowering, improving insulin resistance, inhibiting cell apoptosis, and protecting neurons. However, the mechanism by which salidroside alleviates neuronal degeneration and improves learning and memory impairment in diabetic mice remains unclear. OBJECTIVE: To investigate the effects and mechanisms of salidroside on hippocampal neurons in streptozotocin-induced diabetic mice. MATERIALS AND METHODS: C57BL/6 mice were randomly divided into 4 groups to receive either sham (control group (CON)), diabetes mellitus (diabetes group (DM)), diabetes mellitus + salidroside (salidroside group (DM + SAL)), and diabetes mellitus + salidroside + phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (diabetes mellitus + salidroside + LY294002 group (DM + SAL + LY294002)). After 12 weeks of diabetes onset, the cognitive behaviors were tested using Morris water maze. The number of hippocampal neurons was detected by Nissl staining. The expressions of PI3K, p-PI3K, Akt, p-Akt, GSK-3ß, p-GSK-3ß, cleaved caspase-3, caspase-3, Bax, Bcl-2, MAP2, and SYN in the hippocampus were detected by Western blot. Moreover, the expression of MAP2 and SYN in the hippocampus was further confirmed by immunofluorescence staining. RESULTS: Salidroside increased the time of diabetic mice in the platform quadrant and reduced the escape latency of diabetic mice. Salidroside also increased the expression of p-PI3K, p-Akt, p-GSK-3ß, MAP2, SYN, Bcl-2, while suppressed the expression of cleaved caspase-3, caspase3, and Bax in the DM + SAL group compared with the DM group (P < 0.05). The Nissl staining showed that the number of hippocampus neurons in the DM + SAL group was increased with the intact, compact, and regular arrangement, compared with the DM groups (P < 0.05). Interestingly, the protective effects of salidroside on diabetic cognitive dysfunction, hippocampal morphological alterations, and protein expressions were abolished by inhibition of PI3K with LY294002. CONCLUSIONS: Salidroside exerts neuroprotective properties in diabetic cognitive dysfunction partly via activating the PI3K/Akt/GSK-3ß signaling pathway.

Relationship between IL-22 and IL-22BP in diabetic cognitive dysfunction.

BACKGROUND: CD4 + T helper (Th)22 cells play a regulatory role in autoimmune diseases such as type 1 diabetes mellitus. The Th22-related cytokine interleukin (IL)-22, the expression of which is increased in diabetes mellitus (DM), can act as a neurotrophic factor to protect neurons from apoptosis. Paradoxically, neuronal apoptosis and learning and memory decline occur in DM. In this study, we investigated the relationship between IL-22 and its receptors IL-22Rα1 and IL-22 binding protein (IL-22BP, a soluble inhibitor of IL-22) in diabetic encephalopathy (DE) and the effects of IL-22 on hippocampal neurons, learning and memory. METHODS: A C57BL/6 mouse model of diabetes was constructed by intraperitoneal injection of streptozotocin. The mice were randomly divided into 4 groups: the control group, diabetes group, diabetes + recombinantIL-22 (rIL-22) group and diabetes + IL-22BP group. The Morris water maze test was used to evaluate learning and memory, the expression of IL-22 was measured by ELISA, and Evans Blue staining was used to evaluate blood-brain barrier permeability. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was used to measure the mRNA expression of IL-22 and IL-22Rα1 in the hippocampus. The morphology and number of hippocampal neurons were assessed by Nissl staining, and TUNEL staining was used to detect hippocampal neuronal apoptosis. Immunofluorescence was used to analyze IL-22Rα1 expression and localization in hippocampus, and Western blotting was used to evaluate the expression of IL-22, IL-22Rα1, IL-22BP, and the apoptosis related proteins Caspase-3 and C-caspase-3. RESULTS: Compared with those in the control group, mice in the diabetes group showed cognitive decline; apoptosis of hippocampal neurons; increased expression of hippocampal Caspase-3, C-Caspase-3, IL-22, IL-22Rα1, and IL-22BP; and a decreased IL-22/IL-22BP ratio. Learning and memory were improved, neuronal apoptosis was attenuated, IL-22Rα1 expression and the IL-22/IL-22BP ratio were increased, and caspase-3 and C-caspase-3 expression was decreased in the rIL-22-treated group compared with the diabetes group. IL-22BP treatment aggravated diabetic cognitive dysfunction and pathological alterations in the hippocampus, decreased the IL-22/IL-22BP ratio, and increased the expression of caspase-3 and C-caspase-3 in mice with diabetes. CONCLUSION: A decrease in the IL-22/IL-22BP ratio plays an important role in diabetic cognitive dysfunction, and rIL-22 can effectively alleviate DE. Herein, we shed light on the interaction between IL-22 and IL-22BP as therapeutic targets for DM.

Salidroside Alleviates Diabetic Cognitive Dysfunction Via B3galt2/F3/Contactin Signaling Pathway in Mice.

Diabetes is frequently accompanied by cognitive impairment with insidious onset, and progressive cognitive and behavioral changes. ß-1, 3-galactosyltransferase 2 (B3galt2) contributes to glycosylation, showing a clue for neuronal apoptosis, proliferation and differentiation. However, the role of B3galt2 in diabetic cognitive dysfunction (DCD) has not been investigated. In the present study, we aimed to explore the role of B3galt2 in DCD. Additionally, the potential therapeutic effects of salidroside on DCD was also explored. Diabetic C57BL/6J mice showed cognitive dysfunction together with down-regulated B3galt2. Overexpression of B3galt2 reversed the cognitive decline of diabetic C57BL/6J. Moreover, cognitive impairment was aggravated in B3galt2+/- diabetic mice compared with C57BL/6J diabetic mice. Immunohistochemistry fluorescence indicated that B3galt2 and F3/Contactin were co-localized in the hippocampal regions. Importantly, the expression of F3/Contactin can be regulated by the manipulation of B3galt2, overexpression of which assuaged hippocampal neuronal damage, protected the synapsin, and reduced neuronal apoptosis in diabetic mice. Interestingly, SAL alleviated DCD and reversed the expression of B3galt2 in diabetic C57BL/6J mice. These findings indicate that inhibition of B3galt2/F3/Contactin pathway contributes to DCD, and participates in SAL reversed DCD.

Th22 cells induce Müller cell activation via the Act1/TRAF6 pathway in diabetic retinopathy.

T helper 22 (Th22) cells have been implicated in diabetic retinopathy (DR), but it remains unclear whether Th22 cells involve in the pathogenesis of DR. To investigate the role of Th22 cells in DR mice, the animal models were established by intraperitoneal injection of STZ and confirmed by fundus fluorescein angiography and retinal haematoxylin-eosin staining. IL-22BP was administered by intravitreal injection. IL-22 level was measured by ELISA in vivo and in vitro. The expression of IL-22Rα1 in the retina was assessed by immunofluorescence. We assessed GFAP, VEGF, ICAM-1, inflammatory-associated factors and the integrity of blood-retinal barrier in control, DR, IL-22BP, and sham group. Müller cells were co-cultured with Th22 cells, and the expression of the above proteins was measured by immunoblotting. Plasmid transfection technique was used to silence Act1 gene in Müller cells. Results in vivo and in vitro indicated that Th22 cells infiltrated into the DR retinal and IL-22Rα1 expressed in Müller cells. Th22 cells promoted Müller cells activation and inflammatory factor secretion by secreting IL-22 compared with high-glucose stimulation alone. In addition, IL-22BP ameliorated the pathological alterations of the retina in DR. Inhibition of the inflammatory signalling cascade through Act1 knockdown alleviated DR-like pathology. All in all, the results suggested that Th22 cells infiltrated into the retina and secreted IL-22 in DR, and then IL-22 binding with IL-22Rα1 activated the Act1/TRAF6 signal pathway, and promoted the inflammatory of Müller cells and involved the pathogenesis of DR.