mTOR-dependent TFEB activation and TFEB overexpression enhance autophagy-lysosome pathway and ameliorate Alzheimer's disease-like pathology in diabetic encephalopathy

BACKGROUND: Diabetic encephalopathy (DE) is a complication of type 2 diabetes mellitus (T2DM) that features Alzheimer's disease (AD)-like pathology, which can be degraded by the autophagy-lysosome pathway (ALP). Since transcription factor EB (TFEB) is a master regulator of ALP, TFEB-mediated ALP activation might have a therapeutic effect on DE, but this has yet to be investigated. METHODS: We established T2DM mouse models and cultured HT22 cells under high-glucose (HG) conditions to confirm the role of ALP in DE. To further investigate this, both mice and HT22 cells were treated with 3-methyladenine (3-MA). We also analyzed the content of TFEB in the nucleus and cytoplasm to evaluate its role in ALP. To confirm the effect of TFEB activation at the post-translational level in DE, we used rapamycin to inhibit the mechanistic target of rapamycin (mTOR). We transduced both mice and cells with TFEB vector to evaluate the therapeutic effect of TFEB overexpression on DE. Conversely, we conducted TFEB knockdown to verify its role in DE in another direction. RESULTS: We found that T2DM mice experienced compromised cognitive function, while HG-cultured HT22 cells exhibited increased cell apoptosis. Additionally, both T2DM mice and HG-cultured HT22 cells showed impaired ALP and heavier AD-like pathology. This pathology worsened after treatment with 3-MA. We also observed decreased TFEB nuclear translocation in both T2DM mice and HG-cultured HT22 cells. However, inhibiting mTOR with rapamycin or overexpressing TFEB increased TFEB nuclear translocation, enhancing the clearance of ALP-targeted AD-like pathology. This contributed to protection against neuronal apoptosis and alleviation of cognitive impairment. Conversely, TFEB knockdown lessened ALP-targeted AD-like pathology clearance and had a negative impact on DE. CONCLUSION: Our findings suggest that impaired ALP is responsible for the aggravation of AD-like pathology in T2DM. We propose that mTOR-dependent TFEB activation and TFEB overexpression are promising therapeutic strategies for DE, as they enhance the clearance of ALP-targeted AD-like pathology and alleviate neuronal apoptosis. Our study provides insight into the underlying mechanisms of DE and offers potential avenues for the development of new treatments for this debilitating complication of T2DM. Video abstract.