Insulin and liraglutide attenuate brain pathology in diabetic mice by enhancing the Wnt/β‑catenin signaling pathway

Abstract

Insulin and liraglutide have been demonstrated to control blood glucose and exert neuroprotective effects. However, the impact of liraglutide or insulin alone or in combination on brain pathology in type 1 diabetes mellitus (T1DM) and their underlying mechanisms are unclear. In the present study, diabetes mellitus (DM) was induced via intraperitoneal injection of streptozotocin in mice and subsequently mice were treated with insulin, liraglutide, a combination of the two drugs or saline. Changes in body weight and blood glucose were assessed weekly. The pathological changes in the brain tissue and the apoptosis of neurons were assessed using H&E staining and TUNEL staining. The mRNA and protein expression levels of apoptosis-related proteins were detected using reverse transcription-quantitative PCR (RT-qPCR) and western blotting, respectively. Moreover, Ki67 protein expression was analyzed using immunohistochemistry and the mRNA and protein expression levels of Wnt/β-catenin signaling pathway-related proteins were examined using RT-qPCR and western blotting, respectively. The results of the present study suggested that DM mice developed hyperglycemia and weight loss and also exhibited significantly increased neural cell apoptosis and significantly reduced numbers of Ki67-positive cells. Liraglutide significantly decreased blood glucose levels in DM mice, whereas both insulin and the combination of the two drugs failed to control blood glucose well. Insulin, liraglutide and their combination also failed to control body weight well, but significantly attenuated brain pathological changes and activation of the pro-apoptotic proteins Caspase-3 and Bax, which may have resulted in the significant increase in the expression levels of Wnt/β-catenin signaling pathway-associated molecules such as Wnt3a and S9-pGSK-3β. Liraglutide also promoted the protein expression of the neurogenesis marker of Ki67 and the antiapoptotic factor Bcl-2. These results suggested that insulin and liraglutide may improve brain damage via upregulation of the Wnt/β-catenin signaling pathway and could be of therapeutic relevance for improvement of cognitive impairment in patients with DM.

Insulin signaling promotes neurogenesis in the brain of adult zebrafish

“…In the brain, the protective role of insulin signaling is well documented, particularly in animal models of diabetes and cerebral ischemia, demonstrating the effect of insulin in improving the survival and neurologic scores (Auer, 1998; Zhao et al., 2022). In this context, we examined the expression of genes related to insulin signaling pathway for better understanding the molecular mechanisms that could take place after brain damage.…”

Liraglutide improves sevoflurane-induced postoperative cognitive dysfunction via activating autophagy and inhibiting apoptosis

“…Meanwhile, LRG can penetrate the blood-brain barrier of rodents and plays an important role in regulating central nervous system diseases [ 22 ]. The study shows that LRG has protective effect on cerebral ischemia reperfusion injury in mice [ 23 ]. In addition, LRG improves nonalcoholic steatohepatitis by inhibiting the activation of NLRP3 inflammatory bodies and cell charring [ 24 ].…”

Cognitive dysfunction in diabetes: abnormal glucose metabolic regulation in the brain

“…This point has been proved in some studies. Central injection of liraglutide (an antidiabetic drug) improved memory functions in diabetic rats, which correlated with the ameliorated brain glucose uptake (61). Overexpression of a glucose transporter or stimulation of glucose uptake by metformin attenuated cognitive dysfunction in T2DM, suggesting that the recovery of glucose transport and uptake activities are beneficial to the neuronal function repair (62).…”

“…However, the effect of Wnt signal is partially abolished accompanied by dis-regulated glycolysis. Insulin could attenuate the neuronal damage and cognitive dysfunction in diabetic mice by enhancing the Wnt pathway (61). Therefore, the neuroprotective effects of insulin signaling in DCD mouse models can be attributed, at least in part, to insulin signal-mediated improvement in glucose metabolism and utilization in the glycolysis process.…”