Histone Variant H2A.J Links Epigenetic Reprogramming to Mitochondrial-dependent Kidney Regeneration under Radiation Stress

The histone variant H2A.J is implicated in radiation-induced senescence by promoting the transcription of inflammatory genes. While H2A.J expression increases in renal tubular epithelial cells (TECs) following ionizing radiation (IR), its functional role remains poorly understood. To investigate this, constitutive H2A.J knock-out (KO) mice and wild-type (WT) controls were subjected to CT-guided IR (fractionated whole-body or localized kidney IR). Kidneys were analyzed at acute, intermediate, and chronic stages using immunofluorescence, histochemistry, automated image analysis, and electron microscopy. In WT TECs, IR induced rapid chromatin incorporation and C-terminal serine phosphorylation of H2A.J. Conversely, KO kidneys exhibited significantly more severe histopathological damage, including tubular dilation, flattened epithelium, associated with increased apoptosis, and premature senescence, characterized by persistent DNA damage with lamin B1 loss. Notably, KO TECs displayed disrupted mitochondrial networks and reduced brush borders even at baseline, which were further exacerbated by IR. Unlike WT controls, KO kidneys developed progressive tubular atrophy and incipient fibrosis, indicating a failure in regenerative capacity. Our findings suggest that H2A.J loss impairs tubular regeneration due to defective mitochondrial activation, resulting in insufficient energy supply for coordinated repair. Collectively, these results identify H2A.J as a critical stress-adaptive histone variant essential for the epigenetic regulation of tissue repair following radiation-induced damage. One Sentence SummaryIn irradiated kidney, the loss of histone variant H2A.J impairs the chromatin-mediated adaptation of mitochondrial function in tubular epithelial cells, thereby exacerbating cellular stress - characterized by increased induction of apoptosis and senescence - and ultimately leading to tubular atrophy. Translational RelevanceAcute and chronic kidney injury are frequent complications of genotoxic cancer therapies. Chemo- and radiotherapy induce DNA lesions that trigger cell death and senescence, often leading to irreversible renal damage. However, renal regeneration can occur through the dedifferentiation, proliferation, and redifferentiation of surviving tubular epithelial cells (TECs). This repair process is governed by epigenetic mechanisms that regulate the DNA damage response (DDR) and adapt gene expression programs. Following ionizing radiation (IR), epigenetic remodeling involves the incorporation of histone variants that modulate chromatin accessibility for stress-responsive transcription factors. We identify the histone variant H2A.J as a constitutive component of renal TECs, significantly upregulated after exposure to ionizing radiation (IR). Using H2A.J knock-out (KO) mice, we demonstrate that its absence disrupts acute damage responses and prevents coordinated repair, severely impairing regeneration. Mechanistically, H2A.J deficiency compromises mitochondrial function under postirradiation metabolic stress, driving the transition from acute injury to chronic kidney disease via persistent inflammation and maladaptive tubulointerstitial repair. Targeting these epigenetic drivers offers a promising strategy for regenerating damaged kidney tissue in oncology.