Association between FNDC5 Deficiency and Compromised Mitochondrial Integrity and Biogenesis in Kidney Disease.

Abstract

Background: Mitochondrial dysfunction is a hallmark of acute and chronic kidney diseases. This study investigates the expression landscape and potential association of FNDC5 with renal injury.

Methods: We integrated human scRNA-seq, mouse spatial transcriptomics (ischemia-reperfusion injury model), in vitro high-glucose (HG) models in proximal tubule cells and podocytes, and a constitutive Fndc5 knockout mouse model. Candidate transcription factor occupancy at the FNDC5 promoter was examined by ChIP-qPCR, and associations were assessed in a non-insulin-dependent diabetes mellitus mouse model.

Results: scRNA-seq localized FNDC5 to specific tubules, showing downregulation in diabetic nephropathy. Spatial transcriptomics confirmed a distinct loss of cortical Fndc5 following ischemia-reperfusion injury. In vitro, HG treatment suppressed FNDC5, reduced cell viability, and triggered mitochondrial fragmentation, evidenced by increased DRP1 phosphorylation and downregulated MFN1/OPA1. ZEB1 and CREB1 were identified as candidate transcription factors showing occupancy at the FNDC5 promoter. Genetic deletion of Fndc5 reproduced this fission-permissive shift and reduced PGC1α expression under basal, non-diabetic conditions, providing loss-of-function evidence that Fndc5 deficiency is sufficient to reproduce this phenotype, independent of any additional metabolic stressor. In vivo, diabetic mice exhibited diminished FNDC5 levels, which correlated with an oxidative stress-associated marker (4-HNE) and reduced expression of the biogenesis-associated marker PGC1α.

Conclusion: FNDC5 downregulation is a conserved feature of renal injury associated with mitochondrial fission, and genetic loss-of-function data indicates that Fndc5 deficiency is sufficient to reproduce selected features of this fission-permissive mitochondrial phenotype; whether FNDC5 acts through a defined downstream pathway remains to be established.