N-methyl-d-aspartate receptor hyperfunction contributes to d-serine-mediated renal insufficiency

Glutamate N-methyl-d-aspartate receptor (NMDAR) hyperfunction is known to contribute to acute renal failure due to ischemia-reperfusion and endotoxemia. d-Serine is a coagonist for NMDAR activation, but whether NMDARs play a role in d-serine-mediated nephrotoxicity remains unclear. Here, we demonstrate that NMDAR blockade ameliorated d-serine-induced renal injury. In NMDAR-expressing LLC-PK1 cells, which were used as a proximal tubule model, d-serine but not l-serine induced cytotoxicity in a dose-dependent manner, which was abrogated by the selective NMDAR blockers MK-801 and AP-5. Time-dependent oxidative stress, evidenced by gradually increased superoxide and H2O2 production, was associated with d-serine-mediated cytotoxicity; these reactive oxygen species could be alleviated not only after NMDAR inhibition but also by NADPH oxidase (NOX) inhibition. Activation of protein kinase C (PKC)-δ and PKC-ζ is a downstream signal for NMDAR-mediated NOX activation because PKC inhibition diminishes the NOX activity that is induced by d-serine. Renal injury was further confirmed in male Wistar rats that intraperitoneally received d-serine but not l-serine. Peak changes in glucosuria, proteinuria, and urinary excretion of lactate dehydrogenase and malondialdehyde were found after 24 h of treatment. Persistent tubular damage was observed after 7 days of treatment. Cotreatment with the NMDAR blocker MK-801 for 24 h abolished d-serine-induced functional insufficiency and tubular damage. MK-801 attenuated renal superoxide formation by lowering NOX activity and protein upregulation of NOX4 but not NOX2. These results reveal that NMDAR hyperfunction underlies d-serine-induced renal injury via the effects of NOX4 on triggering oxidative stress.NEW & NOTEWORTHY Ionotropic N-methyl-d-aspartate receptors (NMDARs) are not only present in the nervous system but also expressed in the kidney. Overstimulation of renal NMDARs leads to oxidative stress via the signal pathway of calcium/protein kinase C/NADPH oxidase in d-serine-mediated tubular cell damage. Intervention of NMDAR blockade may prevent acute renal injury caused by d-serine.

P5388N-cadherin promotes cardiac regeneration by stabilizing beta-catenin

Background

Although the adult mammalian heart fails to regenerate after injury, it is known that newborn mice within a week have full cardiac regenerative capacity. The molecular determinants underlying the disparate regenerative capacity between neonatal and adult mice, however, remain incompletely understood. Exploiting RNA sequencing in isolated cardiomyocytes from neonatal and adult mouse heart, we identified Cdh2, which encodes the adherence junction protein N-cadherin, as a potential novel mediator of cardiac regeneration. Cdh2 expression levels were much higher in neonatal, compared with adult, cardiomyocytes and showed a strong positive correlation with that of multiple cell cycle genes. N-cadherin has been reported to be essential for embryonic cardiac development; its role in cardiac regeneration, however, remains unknown.

Purpose

To determine the role of Cdh2 (N-cadherin) in cardiac regeneration and to investigate the underlying molecular mechanisms.

Methods

Apical resection in postnatal day 1 mice was used as a cardiac regenerative model. The in vitro gain/loss-of function studies of Cdh2/N-cadherin was performed in postnatal day 1 neonatal mouse cardiomyocytes (P1CM) and human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM). N-cadherin inhibitor exherin was used to study the effects of N-cadherin in vivo.

Results

Comparing to sham-operated control, Cdh2 was significantly upregulated in mouse cardiac apex and border zone following apical resection, which was accompanied with increased cardiomyocyte proliferation activity. In vitro, knocking down Cdh2 or inhibition of N-cadherin activity with exherin in P1CM significantly reduced the proliferative activity of cardiomyocytes, whereas overexpression of Cdh2 markedly increased the proliferation of P1CM. In addition, forced expression of Cdh2 resulted in significant upregulation of multiple cell cycle genes, including Ccnd1 (Cyclin D1) and Pcna (proliferating cell nuclear antigen), in P1CM. In vivo inhibition of N-cadherin in P1 neonatal mice with exherin following apical resection impaired cardiac regeneration and increased scar formation (Figure). Knocking down CDH2 in human iPSC-CMs significantly reduced the proliferative activity and the expression levels of cell cycle gene CCND1 in iPSC-CMs. Mechanistically, we demonstrated that the pro-mitotic effects of N-cadherin in cardiomyocytes were mediated, at least partially, by stabilizing β-catenin, a pro-mitotic transcription factor, through direct interaction with its cytoplasmic domain and/or inactivation of GSK3β, a critical component of β-catenin destruction complex.

N-Cad blocker impairs heart regeneration

Conclusion

Our study uncovered a previously unrecognized role of Cdh2 (N-cadherin) in cardiomyocyte proliferation and cardiac regeneration. Enhancing cardiac expression or activity of N-cadherin, therefore, could be a potential novel therapeutic approach to promote cardiac regeneration and restore cardiac function in adult heart following injury.

Cloning, sequencing, and expression of the rpoD gene encoding the primary sigma factor of Xanthomonas campestris

A DNA fragment encoding the primary sigma factor from Xanthomonas campestris pv. campestris was cloned and sequenced. The gene (rpoD) encodes a polypeptide of 622 amino acids with a calculated MW of 70,700. The deduced amino acid sequence exhibits extensive sequence homology to the conserved regions of the primary sigma factors from bacteria. The gene product expressed in Escherichia coli, detected by Western blot analysis, had a MW similar to that estimated for the purified protein in SDS-PAGE. The NH2-terminal amino acid sequence determined chemically matched with that deduced from the nucleotide sequence of the rpoD gene. The calculated pI value (9.31) for the X. campestris primary sigma factor is much higher than the values observed for the analogous proteins from other bacteria.