The first day after blood flow is restored to a kidney that has temporarily lost its blood supply is the most lethal period for tubular epithelial cells. Not because of ischemia itself, but because returning blood flow brings a new wave of damage—a biological paradox known as ischemia/reperfusion injury (IRI). This was the focus of research by drg. Finsa Tisna Sari, M.Biomed., Ph.D., and colleagues from the Department of Anatomy, Faculty of Medicine, Public Health, and Nursing (FK-KMK), Universitas Gadjah Mada. Their findings were published in the May 2020 issue of the Medical Journal of Malaysia.
The study revealed a cellular narrative more complex than previously thought: an injured kidney does not simply die or recover—it can also undergo premature aging.
When Blood Returns, Cells Begin to Fall
Acute kidney injury (AKI) caused by IRI is one of the major causes of sudden kidney failure in clinical practice and is associated with high morbidity and mortality. Its mechanisms are complex. Ischemia damages the structure and function of tubular epithelial cells, triggers inflammation, and causes microvascular injury that can further worsen the condition when blood flow is restored.
To map these cellular dynamics in detail, drg. Finsa Tisna Sari and her team used male Swiss-Webster mice aged 3–4 months. Both renal pedicles were clamped for 30 minutes using non-traumatic vascular clamps and then released to induce reperfusion. The mice were subsequently sacrificed on day 1 (I/R1), day 8 (I/R8), and day 12 (I/R12) to capture the dynamics from the acute through chronic phases.
Histological staining with Periodic Acid-Schiff (PAS) revealed substantial damage, including loss of the brush border, disruption of cell polarity, formation of intraluminal casts, and tubular lumen dilation in all injured groups compared with the control group, which underwent sham surgery only.
Three Acts in a Single Injury
RT-PCR and immunohistochemical analyses revealed a clearly structured pattern.
On day 1, expression of Bax, a pro-apoptotic protein from the Bcl-2 family, reached its peak. Renal tubular epithelial cells were undergoing programmed cell death. p53 antibody staining confirmed the location of this apoptosis in the nuclei of tubular epithelial cells. The body was in an extension phase, during which damage spread and the glomerular filtration rate continued to decline.
By day 8, Bcl-2, an anti-apoptotic protein that is also associated with proliferation, became dominant. The cells began attempting to replace those that had been lost. Proliferation occurred in the tubular epithelium, marking a maintenance phase in which the body began consolidating the repair process. But something interesting happened on day 12: both apoptosis and proliferation shifted to the interstitial region rather than remaining in the epithelium. This was not normal recovery. It was a sign of maladaptation.
The most surprising finding was the expression of p16, a marker of cellular senescence. Rather than declining, p16 expression continued to increase over time and reached its highest level during the chronic phase (I/R12). Cells that should either proliferate or undergo apoptosis instead became trapped in a state of permanent arrest. They were neither dead nor functioning normally. These “zombie cells” remained metabolically active while releasing inflammatory and fibrotic signals such as TGF-β and connective tissue growth factor.
“Ischemia/reperfusion injury induces upregulation of proliferation, apoptosis, and cellular senescence in acute kidney injury. Apoptosis reached its peak on day 1, proliferation on day 8, and cellular senescence on day 12.”
This was the research team's conclusion—a precise chronology of three distinct cellular responses occurring within the same organ.
Premature Aging as a Seed of Chronic Kidney Disease
The finding regarding cellular senescence has particularly important clinical implications. Senescent cells do not simply stop functioning. They adopt a senescence-associated secretory phenotype (SASP), releasing IL-8 and other pro-inflammatory cytokines that drive more cells into G2/M arrest. This vicious cycle accelerates tubulointerstitial fibrosis and may contribute to the development of chronic kidney disease (CKD).
In other words, AKI that does not completely recover is not merely a short-term problem. It can leave behind a legacy of a kidney that ages faster than it should.
Funded by a Rekognisi Tugas Akhir (RTA) grant from Universitas Gadjah Mada, the study emphasizes that understanding the mechanisms of cellular senescence in the context of IRI is more than an academic exercise. It represents a potential roadmap toward more targeted therapies, both for preventing AKI and for stopping its progression to CKD.
Cells that refuse to die, refuse to function normally, and continue poisoning their surrounding environment may represent a hidden enemy behind every episode of kidney injury that appears to have recovered.
Authors: Nanda Ayu, drg. Achmad Zam Zam Aghasy, M.Kes.
Photo: Pexels