Characterization of Adult Canine Kidney Epithelial Stem Cells That Give Rise to Dome-Forming Tubular Cells.

Dome formation can occur in cultured tubular epithelial cells originating from various tissues, including the mammary gland and the kidney. The isolation and characterization of normal kidney epithelial stem cells that give rise to dome-forming tubular cells have never been reported. We attempted to isolate and characterize canine kidney epithelial stem cells using a simple cell culture method that we have previously used to isolate other adult human stem cells. Dome-forming kidney epithelial cells were derived from dissociated adult canine kidney tissues that were cultured in a modified keratinocyte serum-free medium supplemented with N-acetyl-l-cysteine, l-ascorbic acid 2-phosphate, nicotinamide, and fetal bovine serum. These cells exhibited high self-renewal capacity in long-term culture (growth for >13 months and 30 cumulative population doublings) and exhibited characteristics of stem cells, including (1) deficiency in gap junctional intercellular communication, (2) anchorage-independent growth, (3) expression of stem cell markers octamer-binding transcription factor 4 and SRY (sex determining region Y)-box 2, (4) expression of cell surface markers CD24 and CD133, and (5) multipotent differentiation into osteoblasts, adipocytes, chondrocytes, and dome-forming tubular cells. Most of these characteristics are shared by the well-known canine renal tubule-derived immortalized Madin-Darby Canine Kidney cell line. Furthermore, the putative canine kidney stem cells developed in this study formed budding tubule-like organoids on Matrigel and required high cell density (>4,000 cells/cm2) for sustained growth and confluency for dome formation. The signal transducer and activator of transcription-3 (STAT3) phosphorylation inhibitor, AG490, inhibited colony-forming efficiency and dome formation, whereas lipopolysaccharide, an activator of STAT3, increased colony-forming efficiency in a dose-dependent manner. These results are consistent with the hypothesis that high cell density induces STAT3 expression, which promotes both stem cell self-renewal and differentiation into tubular cells. Our novel cell culture method should be useful for the future development of normal human kidney stem cells for clinical applications and for studying mechanisms of nephrotoxicity.

Fulvic acid attenuates homocysteine-induced cyclooxygenase-2 expression in human monocytes.

BACKGROUND: Homocysteine and pro-inflammatory mediators such as cyclooxygenase-2 (COX-2) have been linked to vascular dysfunction and risks of cardiovascular diseases. Fulvic acid (FA), a class of compounds of humic substances, possesses various pharmacological properties. However, the effect of FA on inflammatory responses of the monocytes remains unclear. We investigated the regulatory effect of FA on homocysteine-induced COX-2 expression in human monocytes. METHODS: Peripheral blood monocytes and U937 cells were used for all experiments. Real-time PCR and ELISA assay were used to analyze the COX-2 mRNA expression and PGE2 secretion, respectively. Specific inhibitors were used to investigate the mechanism of homocysteine-mediating COX-2 mRNA expression and PGE2 secretion. Luciferase assay, transcription factor ELISA, and chromatin immunoprecipitation were used to determine the role of nuclear factor-κB in FA-mediated inhibition of homocysteine effect on monocytes. RESULTS: The results show that pretreating monocytes with FA inhibited the homocysteine-induced COX-2 expression in a dose-dependent manner. Stimulation of U937 monocytes with homocysteine induced rapid increases in the phosphorylation of ERK and JNK; the inhibitor for ERK and JNK attenuated the homocysteine-induced nuclear factor-κB activation and COX-2 expression. Transcription factor ELISA and chromatin immunoprecipitation assays showed that FA blocked the homocysteine-induced increases in the binding activity and in vivo promoter binding of nuclear factor-κB in monocytes. CONCLUSIONS: Our findings provide a molecular mechanism by which FA inhibits homocysteine-induced COX-2 expression in monocytes, and a basis for using FA in pharmaceutical therapy against inflammation.

Two different approaches to restore renal nitric oxide and prevent hypertension in young spontaneously hypertensive rats: l-citrulline and nitrate.

Nitric oxide (NO) deficiency mediates oxidative stress in the kidney and is involved in the development of hypertension. NO synthesis occurs via 2 pathways: nitric oxide synthase (NOS) dependent and NOS-independent. We tested whether the development of hypertension is prevented by restoration of NO by dietary l-citrulline or nitrate supplementation in young spontaneously hypertensive rats (SHRs). Male SHRs and normotensive Wistar Kyoto control rats (WKYs)s age 4 weeks were assigned to 4 groups: untreated SHRs and WKYs, and SHRs and WKYs that received 0.25% l-citrulline for 8 weeks. In our second series of studies, we replaced l-citrulline with 1 mmol/kg/d sodium nitrate. All rats were sacrificed at age 12 weeks. We found an increase in the blood pressure of SHRs was prevented by dietary supplementation of l-citrulline or nitrate. Both treatments restored NO bioavailability and reduced oxidative stress in SHR kidneys. l-Citrulline therapy reduced levels of l-arginine and asymmetric dimethylarginine (ADMA)-an endogenous inhibitor of NOS-and increased the l-arginine-to-ADMA ratio in SHR kidneys. Nitrate treatment reduced plasma levels of l-arginine and ADMA concurrently in SHRs. Our findings suggest that both NOS-dependent and -independent approaches in the prehypertensive stage toward augmentation of NO can prevent the development of hypertension in young SHRs.