Renal Cells from Spermatogonial Germline Stem Cells Protect against Kidney Injury

Abstract

Spermatogonial stem cells reside in specific niches within seminiferous tubules and continuously generate differentiating daughter cells for production of spermatozoa. Although spermatogonial stem cells are unipotent, these cells are able to spontaneously convert to germline cell-derived pluripotent stem cells (GPSCs) in vitro. GPSCs have many properties of embryonic stem cells and are highly plastic, but their therapeutic potential in tissue regeneration has not been fully explored. Using a novel renal epithelial differentiation protocol, we obtained GPSC-derived tubular-like cells (GTCs) that were functional in vitro, as demonstrated through transepithelial electrical resistance analysis. In mice, GTCs injected after ischemic renal injury homed to the renal parenchyma, and GTC-treated mice showed reduced renal oxidative stress, tubular apoptosis, and cortical damage and upregulated tubular expression of the antioxidant enzyme hemeoxygenase-1. Six weeks after ischemic injury, kidneys of GTC-treated mice had less fibrosis and inflammatory infiltrate than kidneys of vehicle-treated mice. In conclusion, we show that GPSCs can be differentiated into functionally active renal tubular-like cells that therapeutically prevent chronic ischemic damage in vivo, introducing the potential utility of GPSCs in regenerative cell therapy. AKI is a common complication characterized by a rapid reduction in kidney function that results in failure to maintain fluid. AKI is a potentially reversible disease. However, some patients recover incompletely from AKI, and these patients either continue undergoing dialysis or progress to CKD. Moreover, development of CKD can lead to ESRD. One of the main causes of AKI is ischemia/reperfusion injury (IRI). 1 IRI is a pathologic condition characterized by an initial restriction of blood supply followed by the subsequent restoration of perfusion and concomitant reoxygenation that is frequently associated with an exacerbation of tissue injury and a strong inflammatory response. 2 The cells within the renal parenchyma that suffer the most damage upon kidney ischemia are the proximal tubular cells. This is likely due to the presence of a brush border on these cells that increases cell surface area and sensitizes them to damage.The recent discovery of the ability to reprogram adult cells into pluripotent stem cells (iPSCs) has profound therapeutic implications for diseases involving tissue damage and degeneration. Derivation of pluripotent stem cells from an adult source avoids several ethical concerns of obtaining such cells from embryos. However, efficient generation of iPSCs typically requires transduction of cells with reprogramming factors, including potent proto-oncogenes that can limit their therapeutic uses. 3 The existence of inherent epigenetic differences between iPSCs and regular embryonic stem cells (ESCs) can adversely affect iPSCs functionality. 4,5

Long Term Liver Engraftment of Functional Hepatocytes Obtained from Germline Cell-Derived Pluripotent Stem Cells

“…There is also report of GPSC-derived hematopoietic cells homing to bone marrow cavity following intra-bone marrow injection in immune-compromised mice[ 34 ]. Moreover, we recently described the engraftment of GPSC-derived renal tubular cells in mice after renal damage [ 15 ]. To our knowledge, this is the first study demonstrating the engraftment of GPSC-derived hepatocytes in the liver of mice.…”

“…FISH for Y chromosome was performed using mouse Y chromosome (catalogue # 1189-YMF-02; Cambio) according to the manufacturer’s protocol. We also synthesised a biotinylated probe as previously described with the following modifications[ 15 ]. Formalin-fixed and paraffin-embedded liver sections (3.5 μm) were treated with citrate buffer (pH 6) at 80°C for 90 minutes for antigen retrieval.…”

“…GPSCs show high plasticity and several authors have shown that these cells can be induced to differentiate into functional cardiomyocytes, neurons, hematopoietic cells[ 12 – 14 ]. Recently, we demonstrated that functional renal tubular cells can be obtained from GPSCs and can protect mice against kidney ischemia reperfusion injury[ 15 ].…”

Cell-Based Therapies in Acute Kidney Injury (AKI)

“…Nevertheless, artificial procedures can be applied in order to reprogram SSCs into cells with pluripotent behavior. Two methods have been reported, the first involves SSC culturing in leukemia inhibitory factor-containing medium, the second requires co-culturing of SSCs and Mitomycine-C treated embryonic fibroblasts from mice [20]. The ensuing cell population has been defined as Germline cell-derived Pluripotent Stem Cells (GPSCs) [21].…”

“…Nevertheless, the mentioned study did not evaluate post-AKI outcome parameters such as serum creatinine. Another study, published by De Chiara and colleagues employed GPSCs instead and found the in vitro -differentiation of renal tubular like cells accompanied by significant AKI-protection in the long-term: interstitial fibrosis and inflammation were reduced at week 6 post-injury [20]. As oposed to iPSCs, (SSCs and) GPSCs apparently act by direct mechanisms and not by modifying the post-ischemic milieu through paracrinic and/or other vesicular-dependent mechanisms.…”