Age-Related Downregulation of TFEB Activity in Proximal Tubules Affects Systemic Lipid Metabolism and Causes Apolipoprotein A4-Related Amyloidosis

Background: Transcription factor EB (TFEB) is important for longevity in Caenorhabditis elegans and age-related deterioration of several organs in mice. However, the role of TFEB in proximal tubules remains unknown. Methods: We investigated TFEB nuclear translocation in mouse kidneys and human kidney biopsy samples. We generated TFEB proximal tubular epithelial cell (PTEC)-conditional knockout mice (TFEB cKO mice). Wild-type mice and TFEB cKO mice were bred for up to 24 months to elucidate the role of TFEB in PTECs of aged mice. Results: TFEB nuclear translocation in PTECs was decreased in aged mice and older patients. Surprisingly, amyloid fibrils were prominently deposited in the glomeruli and the interstitium of several aged TFEB cKO mice. To identify amyloidogenic proteins, we isolated glomeruli by laser-capture microdissection and subject the sample to proteomics. Proteomic analyses indicated that apolipoprotein A4 (ApoA4) was the primary candidate. Indeed, ApoA4 was highly positive, corresponding to the distribution of amyloid deposits, and the hepatic Apoa4 mRNA was increased. We found that hepatic steatosis was more severe in aged TFEB cKO mice, which may upregulate hepatic ApoA4, as previously reported. In addition, we verified white adipose tissue hypertrophy and increased circulating free fatty acids in aged TFEB cKO mice. These indicate that TFEB deficiency in PTECs of aged mice causes metabolic disorders. To further elucidate the role of TFEB in PTECs, we performed scRNA-seq analyses of the kidneys. The scRNA-seq analyses showed that both oxidative phosphorylation (OXPHOS) and lysosome pathways were downregulated in the PTECs of aged TFEB cKO mice. Electron microscopy revealed that the number of mitochondria-lysosome-related organelles, which are involved in mitochondrial quality control dependent on lysosomal function, was increased in the PTECs of aged TFEB cKO mice. Reflecting these results, succinate dehydrogenase staining, indicative of mitochondrial function, was also deteriorated in the PTECs of aged TFEB cKO mice. Conclusion: TFEB deficiency in PTECs of aged mice induces metabolic disorder due to dysfunction of both OXPHOS and lysosome pathways, likely contributing to ApoA4-related amyloidosis. Funding: Private Foundation Support, Government Support – Non-U.S.