The Molecular Mechanism Of Berberine On Cognitive Function In Type 2 Diabetic Encephalopathy Rats

Part 1 Mechanisms of berberine on axonopathy in type 2 diabetic encephalopathy rat modelBackground: Diabetic encephalopathy is a serious complication of the central nervous system in diabetes.Progressive cognitive impairment is its main clinical manifestation.The main pathological features are Alzheimer disease(AD)-like pathological changes in the brain,which contain neurofibrillary tangles(NFTs)forming due to hyperphosphorylation of tau protein or senile plaque(SP)forming caused by the deposition of amyloid β-protein(Aβ),but its exact pathogenesis is not yet clear.Recently,a large number of studies have shown that axonopathy earlier than the two distinguishable characteristic pathological changes,and it is considered as one of the important nosogenesis in AD.But whether the axonopathy is involved in the pathogenesis progression of diabetic encephalopathy is still unknown,pending for further study.Other studies showed that berberine can effectively relieve insulin resistance to prevent and treat type 2 diabetic in periphery.Some studies found that berberine can freely penetrate the blood-brain barrier and accumulate in hippocampus.Berberine has been shown to hold promising effect to neuronal damage in diabetes,but its mechanisms remains to be further elucidated.This paper aimed to investigate the molecular mechanisms about high glucose-induced axonal lesions in neurons and the protective effectes of berberine on high glucose-induced neuronal axonal injury in vitro and in vivo.Experimental approach: First,the diabetic encephalopathy rat model was induced by high glucose/high fat diet and streptozotocin(STZ)injection.Subsequently,the model rats were given berberine by gavage for 10 weeks,and the spatial learning and memory abilities of the rats were detected by the Morris water maze test.At the same time,the axonal morphology of the rat hippocampal neurons was detected using the neuronal tracing by BDA;IF(immunofluorescence)and Western-blot techniques were used to detect protein localization and expression.Secondly,the effects of high glucose stimulation on the axonal transport of neurons and the protective effect of berberine were examined using TIRFM in primary neurons;PI3K inhibitor LY294002 and insulin signaling pathway activator Insulin were further used to uncover the possible molecular mechanisms.Key Results: The hippocampal neuronal axonal lesions were induced in vivo and in vitro,which was accompanied with hyperphosphorylation of tau protein.These changes led to cognitive impairment in type 2 diabetic encephalopathy model rats.Berberine can significantly reduce peripheral blood glucose and serum insulin levels and effectively relieve peripheral insulin resistance in type 2 diabetic encephalopathy model rats.It can largely improve the learning and memory impairment and axonal pathological changes of brain neurons in model rats.Further studies showed that berberine can greatly reduce the phosphorylation of tau protein in model rats and the activity of GSK3β by up-regulating PI3K/Akt signaling pathway.After the primary neurons was treated with high glucose(45 m M)for 24 hours,the PI3K/Akt signaling pathway was inactivation and the phosphorylation level of GSK3β ser 9 was significantly decreased which resulted in a significant increase with GSK3β activity and a significantly increase of phosphorylation level of tau.These terrible effects can be reversed by intervention with berberine.Berberine can significantly improve the high glucose-induced axonal transport impairment in primary neurons.In addition,when the primary neurons were treated with the PI3 K inhibitor LY294002 and/or the insulin signaling pathway activator insulin,the results showed that the administration of LY294002 blocked PI3K/Akt signaling pathways,and LY294002 treatment attenuated the ability of reducing tau phosphorylation by berberine,while the insulin treatment effectively reversed the blocking effect of LY294002 on berberine.Conclusions: Berberine exerts the protective effect against cognitive deficits via improving tau hyperphosphorylation and the axonal damage through restoring PI3K/Akt/GSK3β signaling pathway.Part 2 The mechanism of berberine on the production of Aβ in type 2 diabetic encephalopathy rat modelBackground: With the improvement of material living standards and disease treatment,the lifetime of diabetic patients are obviously prolonged.At the same time,the complications caused by diabetes have gradually attracted researchers’ attention.Moreover,the incidence of neuropathy is the highest among diabetic complications.Diabetic encephalopathy,a proven complication of diabetes,is associated with the progressive development of end-organ injuries in the CNS.In addition,it is formed accompany with cognitive impairment and severely threatens the quality of life in diabetic patients.It has been reported in the literature that chronic inflammatory infiltration in diabetic models led to the occurrence of insulin resistance.Peripheral insulin resistance can lead to the impairments of memory,executive functions deficits and language understanding damage.The marker of AD Alzheimer’s disease,a toxic oligopeptide protein Aβ42,also increased.There have been reports that the medial prefrontal cortex(m PFC)has the function to coordinate information monitoring and processing.The neural circuit of m PFC in the brain is directly related to various forms of memory.Clinical studies have shown that terrible executive function and memory impairment in T2 D are closely related to poor glucose uptake/metabolism in the m PFC,temporal and cerebellar regions.Berberine,a small molecule compound derived from natural products,has shown excellent anti-inflammatory and hypoglycemic effects in diabetic peripheral tissues.However,in the central nervous system,the role of berberine on m PFC in diabetic rats is rarely reported.To better understand the effects of berberine on cognitive function in diabetic patients,we used a model of STZ-induced type 2 diabetes to study the molecular mechanisms of berberine in antagonizing the inflammatory response of m PFC in diabetic rats or improving insulin resistance.Methods: Intragastric administration of berberine(200 mg/Kg/d)was used in diabetic rats.Fear-condition assay was applied for cognitive assessment,and relative protein expressions were detected by western-blot.The glucose uptake in prefrontal cortex of diabetic rats was tested by Positron-Emission Tomography(PET)imaging.The levels of inflammation mediators were determined by commercial ELISA kits.Aβ42 level in m PFC was detected by immunohistochemistry.Results: Firstly,we performed PET experiments in vivo and found that berberine promoted glucose uptake in m PFC of diabetic rats.Subsequently,the results of Western and immunofluorescence showed that berberine can significantly inhibit the release of inflammatory mediators,relieve insulin resistance,and inactivate the MAPK signaling pathway in m PFC of diabetic rats.At the same time,the expression levels of PKCη and PKC ε and NF-κB translocation in neurons was effectively suppressed.In addition,the neuron-specific glucose transporter GLUT3 was also significantly increased 2-3 fold.Moreover,berberine also reduced the expression of amyloid precursor protein(APP)and BACE-1 and the production of oligomer Aβ 42.Finally,behavioral test data showed that treatment with berberine accelerated the processing of information and enhanced memory function in diabetic rats,thereby alleviating cognitive impairment.Conclusion: Berberine inhibited the activation of inflammation pathway and insulin resistance in the m PFC of diabetic rats.Finally,it improved cognition lesion in diabetic rats.