Caspase-3-Independent Internucleosomal DNA Fragmentation in Ischemic Acute Kidney Injury

Abstract

Background/Aims: Renal tubular cell death in ischemia-reperfusion does not follow the classical apoptosis or necrosis phenotype. We characterized the morphological and biochemical features of injured tubular epithelial cells in ischemic acute kidney injury (AKI). Methods: Ischemic AKI was induced in rats by 60 min of ischemia followed by 24 h of reperfusion. Light and electron microscopic TUNEL (LM-TUNEL and EM-TUNEL), gel electrophoresis of extracted DNA, and caspase-3 involvement were examined during the development of death. Results: Damaged tubular epithelial cells with condensed and LM-TUNEL-positive (+) nuclei were prominent at 12 and 18 h after reperfusion with DNA ‘ladder’ pattern on gel electrophoresis. EM-TUNEL+ cells were characterized by nuclei with condensed and clumping chromatin, whereas the cytoplasm showed irreversible necrosis. The protein levels and activity of caspase-3 did not increase in kidneys after reperfusion. In addition, caspase inhibitor (ZVAD-fmk) failed to inhibit DNA fragmentation and prevent tubular epithelial cell death in ischemic AKI. Conclusion: Caspase-3-independent internucleosomal DNA fragmentation occurs in injured tubular epithelial cells undergoing irreversible necrosis in ischemic AKI. The manner of this cell death may be identical to the cell death termed apoptotic necrosis, aponecrosis, or necrapoptosis. Ischemia-reperfusion injury activates caspase-3-independent endonuclease, which in turn induces irreversible damage of tubular epithelial cells, and may contribute to the initiation and development of AKI.

Autophagy Function and Regulation in Kidney Disease

“…Our understanding of the various modes of cell death in renal injury is likely limited by methodology. For example, DNA fragmentation determined by the TUNEL assay has been used as a hallmark of apoptosis in in vivo renal injury studies in animal models; however, the TUNEL assay cannot be considered as conclusive for apoptosis [206] because DNA fragmentation also occurs in necroptosis [207]. Also, the pan-caspase inhibitor zVAD does not provide protection against tubular damage or loss of renal function in renal IRI [208].…”

Transplantation and Damage-Associated Molecular Patterns (DAMPs)

“…Since these topics have recently taken center stage in the research field of stress responses → RCD → immunity, they will be detailed below. In particular, the impact of IRI on necroptosis, parthanatos, and (more pronounced) ferroptosis , ER stress/UPR , ER stress/UPR/autophagy , and DDR has recently been highlighted. These reports clearly attest IRI to be critically implicated in the emission of a plethora of DAMPs inherently capable—via recognition by PRRs on/in cells of the innate immune system—to instigate various inflammatory and adaptive immune pathways promoting, for example, acute and chronic allograft rejection.…”

ELABELA and an ELABELA Fragment Protect against AKI

“…5,8,9 DNA damage, such as apoptosis-associated DNA cleavage in renal tubular cells, occurs in renal I/R injury. 10,11 On DNA damage, cells activate a network of signaling pathways known as DNA damage response (DDR) that initiate with the activation of sensors, including ataxia telangiectasis mutated (ATM) and ataxia telangiectasis and Rad3 related (ATR) protein kinases. 12,13 ATM and ATR phosphorylate mediators, which further recruit transducers, such as checkpoint kinase 1 and 2 (Chk1/2), to phosphorylate effectors and regulate DNA repair, cell cycle arrest, and cell death.…”