According to the Global Observatory on Donation and Transplantation, kidney transplantation accounts for approximately 60%-65% of all solid organ transplants worldwide, with the number of procedures performed in 2023 being nearly three times higher than that of liver transplants, the latter being the second most common type. In 61% of kidney transplants performed that year, the organ originated from deceased donors1, which involves a longer preservation period compared to transplants from living donors, where the waiting time is significantly shorter2. During this preservation period, kidneys are usually preserved using static cold storage in order to slow down cellular metabolism, which reduces oxygen and energy demand and therefore limits ischemic injury3. However, static cold storage provides only partial protection, as it cannot fully sustain cellular metabolism or oxygen delivery, leading to progressive metabolic dysfunction during preservation4,5. Alternatively, ex vivo normothermic preservation has emerged as a viable strategy to maintain the organ at near-physiological temperature, thereby supporting cellular metabolism and oxygenation, and consequently reducing ischemia-reperfusion injury (IRI)6.
However, during kidney transplantation, acute kidney injury (AKI) due to IRI is an unavoidable consequence. IRI results from the interruption of blood flow through the organ, leading to an imbalance between the supply and demand of oxygen and nutrients7. This process has a direct impact on the function of the transplanted kidney, and increases the risk of acute rejection and reduced long-term graft function8,9.
PTECs-especially abundant in the renal cortex-are particularly vulnerable to IRI. These cells constitute approximately 60%-70% of the tubular epithelium and are responsible for the reabsorption of most of the glomerular filtrate, including water, ions, glucose, and amino acids10. Their high metabolic activity is supported by an extensive mitochondrial network to meet ATP-dependent transport demands11. Consequently, they are extremely sensitive to metabolic disturbances, such as oxygen deprivation and mitochondrial dysfunction, both of which are central features of IRI12.
During IRI, the deprivation of oxygen disrupts mitochondrial oxidative phosphorylation, leading to ATP depletion and impaired reabsorption function13,14. This initiates a metabolic switch from fatty acid oxidation (FAO) to anaerobic glycolysis and activation of the pentose phosphate pathway, which, while temporarily protective, is insufficient to fully meet the energetic and redox demands of these cells15. If the suppression of FAO persists during the repair phase, lipid accumulation16 and lipotoxicity ensue17, further damaging the cells and impairing their regenerative capacity18. This maladaptive metabolic state can ultimately drive tubular atrophy, interstitial fibrosis, and progression to chronic kidney disease19.
This metabolic impairment, driven by defective FAO, hinders the ability to meet the high energetic demands of the renal tubule17,19. The resulting ATP depletion and lipid accumulation promote mitochondrial dysfunction and generation of reactive oxygen species, which activate pro-inflammatory signaling and leukocyte infiltration20,21,22. Persistent inflammation and oxidative injury destabilize mitochondrial integrity, amplifying energy failure and eventually triggering apoptotic and necrotic cell death23,24. During this acute-injury phase, specific biomarkers such as Kidney Injury Molecule 1 (KIM-1) and Neutrophil Gelatinase-Associated Lipocalin (NGAL) are upregulated, serving as sensitive indicators of proximal tubular damage and early AKI25.
Following acute injury, maladaptive repair mechanisms promote excessive extracellular matrix deposition, a hallmark of renal fibrosis26. Among the extracellular matrix components, collagen, particularly type I collagen (encoded by the Col1a1 gene), accumulates in the interstitial space, contributing to tubular atrophy and loss of functional parenchyma27. This fibrotic remodeling is largely driven by tubular senescence and partial epithelial-to-mesenchymal transition (pEMT) in tubular epithelial cells, ultimately leading to kidney functional decline28,29,30. The onset of renal pEMT and fibrosis assists the progression from AKI to chronic kidney disease (CKD), culminating in an irreversible loss of kidney function and compromised graft survival31,32.
In this protocol, we describe an in vitro model of H/R injury using mouse SV40-immortalized proximal tubular epithelial cells (IM-PTECs), subjected to controlled H/R conditions. Most preclinical studies of renal IRI have traditionally relied on animal models, which reproduce the complex vascular and immune responses of the kidney but entail higher costs, ethical concerns, and considerably higher biological variability33,34. These limitations have slowed the development of complementary cell-based systems valid for detailed mechanistic and high-throughput studies. This experimental setup allows for the reproducible simulation of oxygen deprivation and restoration, mimicking key features of IRI observed in transplanted kidneys. The model serves as a valuable tool for studying the cellular and molecular mechanisms underlying tubular injury, biomarker expression, and fibrotic responses in a controlled environment. Moreover, it provides a relevant platform for the screening and evaluation of potential therapeutic strategies aimed at preventing or mitigating ischemic damage and improving post-transplant outcomes.