Kallikrein-modified mesenchymal stem cell implantation provides enhanced protection against acute ischemic kidney injury by inhibiting apoptosis and inflammation

Potential advantages of acute kidney injury management by mesenchymal stem cells

Mesenchymal stem cells are currently considered as a promising tool for therapeutic application in acute kidney injury (AKI) management. AKI is characterized by acute tubular injury with rapid loss of renal function. After AKI, inflammation, oxidative stress and excessive deposition of extracellular matrix are the molecular events that ultimately cause the end-stage renal disease. Despite numerous improvement of supportive therapy, the mortality and morbidity among patients remain high. Therefore, exploring novel therapeutic options to treat AKI is mandatory. Numerous evidence in animal models has demonstrated the capability of mesenchymal stem cells (MSCs) to restore kidney function after induced kidney injury. After infusion, MSCs engraft in the injured tissue and release soluble factors and microvesicles that promote cell survival and tissue repairing. Indeed, the main mechanism of action of MSCs in tissue regeneration is the paracrine/endocrine secretion of bioactive molecules. MSCs can be isolated from several tissues, including bone marrow, adipose tissue, and blood cord; pre-treatment procedures to improve MSCs homing and their paracrine function have been also described. This review will focus on the application of cell therapy in AKI and it will summarize preclinical studies in animal models and clinical trials currently ongoing about the use of mesenchymal stem cells after AKI.

Kallikrein-kinin in stem cell therapy

The tissue kallikrein-kinin system exerts a wide spectrum of biological activities in the cardiovascular, renal and central nervous systems. Tissue kallikrein-kinin modulates the proliferation, viability, mobility and functional activity of certain stem cell populations, namely mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs), mononuclear cell subsets and neural stem cells. Stimulation of these stem cells by tissue kallikrein-kinin may lead to protection against renal, cardiovascular and neural damage by inhibiting apoptosis, inflammation, fibrosis and oxidative stress and promoting neovascularization. Moreover, MSCs and EPCs genetically modified with tissue kallikrein are resistant to hypoxia- and oxidative stress-induced apoptosis, and offer enhanced protective actions in animal models of heart and kidney injury and hindlimb ischemia. In addition, activation of the plasma kallikrein-kinin system promotes EPC recruitment to the inflamed synovium of arthritic rats. Conversely, cleaved high molecular weight kininogen, a product of plasma kallikrein, reduces the viability and vasculogenic activity of EPCs. Therefore, kallikrein-kinin provides a new approach in enhancing the efficacy of stem cell therapy for human diseases.

Association of functional kallikrein-1 promoter polymorphisms and acute kidney injury: a case-control and longitudinal cohort study

BACKGROUND

Kallikrein-1 (KLK1) is a highly conserved serine protease that is expressed in the kidney and involved in blood pressure regulation. The activity of this enzyme is diminished in acute kidney injury (AKI).

METHODS

We first evaluated the potential role of functional multiallelic KLK1 promoter gene polymorphisms in a case-control study of 481 subjects (214 hospitalized patients with AKI of mixed causes and 267 healthy subjects). The complex, multiallelic G/C-rich repeat region of the proximal KLK1 promoter was determined by direct Sanger/capillary resequencing.

RESULTS

16 alleles were identified in a complex, polymorphic G/C-rich region of the KLK1 proximal promoter; 5 of these alleles (F, G, H, I, and K) were associated with development of AKI. Alleles I and G were classified as risk-alleles (unadjusted OR 1.86; 95% CI 1.23, 2.81; p = 0.003), whereas alleles F, H, and K were classified as protective-alleles (unadjusted OR 0.32; 95% CI 0.22, 0.46; p < 0.001) according to their directional association with development of AKI. After adjustment for sex, race, preexisting chronic kidney disease and APACHE II score, the KLK1 risk-allele (I or G) carrier state was associated with the composite of ≥2-fold increase in serum creatinine, oliguria, or dialysis requirement (adjusted OR 2.71; 95% CI 1.14, 6.44; p = 0.02). The KLK1 risk-allele carrier state was also marginally associated with the composite of ≥2-fold increase in serum creatinine, oliguria, dialysis requirement, or in-hospital death (adjusted OR 2.33; 95% CI 0.98, 5.52; p = 0.06).

CONCLUSIONS

KLK1 promoter polymorphisms are associated with development of AKI and adverse outcomes. Further studies are needed to validate these findings.