Synergistic Exacerbation of Mitochondrial and Synaptic Dysfunction and Resultant Learning and Memory Deficit in a Mouse Model of Diabetic Alzheimer’s Disease

Diabetes is considered to be a risk factor in Alzheimer’s disease (AD) pathogenesis. Although recent evidence indicates that diabetes exaggerates pathologic features of AD, the underlying mechanisms are not well understood. To determine whether mitochondrial perturbation is associated with the contribution of diabetes to AD progression, we characterized mouse models of streptozotocin (STZ)-induced type 1 diabetes and transgenic AD mouse models with diabetes. Brains from mice with STZ-induced diabetes revealed a significant increase of cyclophilin D (CypD) expression, reduced respiratory function, and decreased hippocampal long-term potentiation (LTP); these animals had impaired spatial learning and memory. Hyperglycemia exacerbated the upregulation of CypD, mitochondrial defects, synaptic injury, and cognitive dysfunction in the brains of transgenic AD mice overexpressing amyloid-β as shown by decreased mitochondrial respiratory complex I and IV enzyme activity and greatly decreased mitochondrial respiratory rate. Concomitantly, hippocampal LTP reduction and spatial learning and memory decline, two early pathologic indicators of AD, were enhanced in the brains of diabetic AD mice. Our results suggest that the synergistic interaction between effects of diabetes and AD on mitochondria may be responsible for brain dysfunction that is in common in both diabetes and AD

Oxidative stress-mediated activation of extracellular signal-regulated kinase contributes to mild cognitive impairment-related mitochondrial dysfunction

Mild cognitive impairment (MCI) occurs during the pre-dementia stage of Alzheimer’s disease (AD) and is characterized by a decline in cognitive abilities that frequently represents a transition between normal cognition and AD dementia. Its pathogenesis is not well understood. Here, we demonstrate the direct consequences and potential mechanisms of oxidative stress, mitochondrial dynamic and functional defects in MCI-derived mitochondria. Using cytoplasmic hybrid (cybrid) cell model in which mitochondria from MCI or age-matched non-MCI subjects were incorporated into a human neuronal cell line depleted of endogenous mitochondrial DNA, we evaluated the mitochondrial dynamics and functions, as well as the role of oxidative stress in the resultant cybrid lines. We demonstrated increased expression levels of mitofusin 2 (Mfn2) is markedly induced by oxidative stress in MCI-derived mitochondria along with aberrant mitochondrial functions. Inhibition of oxidative stress rescues MCI-impaired mitochondrial fusion/fission balance as shown by the suppression of Mfn2 expression, attenuation of abnormal mitochondrial morphology and distribution, and improvement in mitochondrial function. Furthermore, blockade of MCI related stress-mediated activation of extracellular signal-regulated kinase (ERK) signaling not only attenuates aberrant mitochondrial morphology and function but also restores mitochondrial fission and fusion balance, in particular inhibition of overexpressed Mfn2. Our results provide new insights into the role of the oxidative stress-ERK-Mfn2 signal axis in MCI-related mitochondrial abnormalities, indicating that the MCI phase may be targetable for the development new therapeutic approaches that improve mitochondrial function in age-related neurodegeneration

Association between psychiatric disorders and glioma risk: evidence from Mendelian randomization analysis

Abstract Background Observational studies have explored the association of psychiatric disorders and the risk of brain cancers. However, the causal effect of specific mental illness on glioma remains elusive due to the lack of solid evidence. Methods We performed a two-sample bidirectional Mendelian randomization (MR) analysis to explore the causal relationships between 5 common psychiatric disorders (schizophrenia, major depressive disorder, bipolar disorder, autism spectrum disorder, and panic disorder) and glioma. Summary statistics for psychiatric disorders and glioma were extracted from Psychiatric Genomics Consortium (PGC) and 8 genome-wide association study (GWAS) datasets respectively. We calculated the MR estimates for odds ratio of glioma associated with each psychiatric disorder by using inverse-variance weighting (IVW) method. Sensitivity analyses such as weighted median estimator, MR-Egger and MR-PRESSO were leveraged to assess the strength of causal inference. Results A total of 30,657 participants of European ancestry were included in this study. After correction for multiple testing, we found that genetically predicted schizophrenia was associated with a statistically significant increase in odds of non-glioblastoma multiforme (non-GBM) (OR = 1.13, 95% CI: 1.03–1.23, P = 0.0096). There is little evidence for the causal relationships between the other 4 psychiatric disorders with the risk of glioma. Conclusions In this MR analysis, we revealed an increased risk of non-GBM glioma in individuals with schizophrenia, which gives an insight into the etiology of glioma

Additional file 1 of Association between psychiatric disorders and glioma risk: evidence from Mendelian randomization analysis

Supplementary Table 1 Summary of 8 glioma GWAS dataset