N-myc downstream-regulated gene 4, up-regulated by tumor necrosis factor-α and nuclear factor kappa B, aggravates cardiac ischemia/reperfusion injury by inhibiting reperfusion injury salvage kinase pathway.

N-myc downstream-regulated gene 4 (NDRG4) is expressed weakly in heart and has been reported to modulate cardiac development and QT interval duration, but the role of NDRG4 in myocardial ischemia/reperfusion (I/R) injury remains unknown. In the present study, we analyzed the expression as well as potential function of cardiac NDRG4 and investigated how NDRG4 expression is regulated by inflammation. We found that NDRG4 was weakly expressed in cardiomyocytes and that its expression increased significantly both in I/R injured heart and in hypoxia-reoxygenation (H/R) injured neonatal rat ventricular myocytes (NRVMs). The increased NDRG4 expression aggravated myocardial I/R injury by inhibiting the activation of the reperfusion injury salvage kinase (RISK) pathway. Forced over-expression of NDRG4 inhibited RISK activation and exacerbated injury not only in I/R injured heart, but also in H/R treated NRVMs, whereas short hairpin RNA (shRNA)-mediated knock-down of NDRG4 enhanced RISK activation and attenuated injury. Upon injury, myocardial NDRG4 expression was induced by tumor necrosis factor-α (TNF-α) through nuclear factor kappa B (NF-κB), and we found that pre-treatment with inhibitors of either TNF-α or NF-κB blocked NDRG4 expression as well as I/R injury in vivo and H/R injury in vitro. Our study indicates that up-regulation of NDRG4 aggravates myocardial I/R injury by inhibiting activation of the RISK pathway, thereby identifying NDRG4 as a potential therapeutic target in I/R injury.

Up-regulation of NDRG2 through nuclear factor-kappa B is required for Leydig cell apoptosis in both human and murine infertile testes.

Many pro-apoptotic factors, such as nuclear factor-kappa B (NF-κB) and Fas, play crucial roles in the process of Leydig cell apoptosis, ultimately leading to male sterility, such as in Sertoli cell only syndrome (SCO) and hypospermatogenesis. However, the molecular mechanism of such apoptosis is unclear. Recent reports on N-myc downstream-regulated gene 2 (ndrg2) have suggested that it is involved in cellular differentiation, development, and apoptosis. The unique expression of NDRG2 in SCO and hypospermatogenic testis suggests its pivotal role in those diseases. In this study, we analyzed NDRG2 expression profiles in the testes of normal spermatogenesis patients, hypospermatogenesis patients, and SCO patients, as well as in vivo and in vitro models, which were Sprague-Dawley rats and the Leydig cell line TM3 treated with the Leydig cell-specific toxicant ethane-dimethanesulfonate (EDS). Our data confirm that NDRG2 is normally exclusively located in the cytoplasm of Leydig cells and is up-regulated and translocates into the nucleus under apoptotic stimulations in human and murine testis. Meanwhile, transcription factor NF-κB was activated by EDS administration, bound to the ndrg2 promoter, and further increased in expression, effects that were abolished by NF-κB inhibitor Pyrrolidine dithiocarbamate (PDTC). Furthermore, siRNA knock-down of ndrg2 led to increased proliferative or decreased apoptotic TM3 cells, while over-expression of ndrg2 had the reverse effect. This study reveals that ndrg2 is a novel gene that participates in Leydig cell apoptosis, with essential functions in testicular cells, and suggests its possible role in apoptotic Leydig cells and male fertility.

Discoidin domain receptor 2 expression increases phagocytotic capacity in sertoli cells of sertoli cell-only syndrome testes.

Discoidin domain receptor 2 (DDR2) belongs to the receptor tyrosine kinase (RTK) family, other RTKs have been reported to regulate phagocytic function of Sertoli cells (SCs), yet little is known about the function of DDR2 in Sertoli cells. In the present study, we aim to explore the function and mechanism of ectopic discoidin domain receptor 2 (DDR2) expression in Sertoli cells of Sertoli cell-only syndrome (SCOS) testes. We found that discoidin domain receptor 2 (DDR2) was absent in Sertoli cells of normal testis but was expressed in Sertoli cells of SCOS testes. This Sertoli cell DDR2 expression was induced by impaired androgen receptor (AR) signaling, but was inhibited by increased AR signaling from testosterone administration. The Sertoli cell DDR2 expression led to an increase in phagocytosis through up-regulation of Scavenger receptor class B member 1 (SR-BI) levels. However, loss of DDR2 by knock-out or knock-down weakened the phagocytotic capacity of Sertoli cells. Furthermore, the expression of DDR2 in Sertoli cells activated matrix metallopeptidase 9 (MMP-9) to consume abnormal collagen increase in seminiferous tubules which was responsible for the block of testosterone transportation and AR loss and to compensate for the impaired blood-testis-barrier (BTB). Our data suggest that the AR/DDR2 cascade may serve as a negative feedback mechanism to help compensate for the homeostasis of seminiferous epithelium in SCOS testis.

Abnormal Accumulation of Collagen Type I Due to the Loss of Discoidin Domain Receptor 2 (Ddr2) Promotes Testicular Interstitial Dysfunction.

BACKGROUND: Loss of functional allele for discoidin domain receptor 2 (Ddr2) results in impaired Leydig cell response to luteinizing hormone (LH), low testosterone production and arrested spermatogenesis in older male Ddr2slie/slie mice. However, the underlying mechanism responsible for this phenotype remains unknown. Herein, we reported for the first time that the deregulated expression of Ddr2 cognate ligand, namely collagen type I (COL1), may account for the disruption of the testicular steroidogenesis in Ddr2slie/slie mutant testes. METHODOLOGY/PRINCIPAL FINDINGS: Expression of Ddr2 increased gradually along postnatal development, whereas COL1 expression became negligible from adulthood onwards. In Ddr2slie/slie mutant testis, however, in contrast to the undetectable staining of Ddr2, COL1 expression was constantly detected, with the highest values detected during adulthood. In the experimental vasectomy model, Ddr2slie/slie mutant mice exhibited an early androgen deficiency than wild-type mice, along with the accumulation of fibrotic tissue in the interstitium. Functionally, ablation of endogenous Ddr2 resulted in a significant decrease of testosterone (T) level in TM3 cells in the presence of higher concentration of COL1 treatment. Conversely, overexpression of Ddr2 could help TM3 cells to maintain a normal testicular steroidogenesis even in the presence of high concentration of COL1. Additionally, attenuated expression of Ddr2 correlates to the deregulated level of serum T levels in human pathological testes. CONCLUSIONS: Abnormal accumulation of interstitial COL1 may be responsible for the steroidogenic dysfunction in Ddr2slie/slie mutant testes.

Inhibition of ghrelin signaling improves the reproductive phenotype of male ob/ob mouse.

OBJECTIVE: To investigate whether ghrelin signaling is involved in the pathogenesis of male factor infertility induced by leptin deficiency. DESIGN: Experimental study. SETTING: University academic medical center. ANIMAL(S): Ten-week-old C57BL/6J mice and ob/ob mice. INTERVENTION(S): Western blotting, (quantitative) reverse transcription-polymerase chain reaction (qRT-PCR), immunohistochemistry, and in situ end labeling of fragmented DNA. MAIN OUTCOME MEASURE(S): Expression levels of ghrelin and its functional receptor growth hormone (GH) secretagogue receptor 1a (GHS-R1α) were examined by Western blotting and immunohistochemistry. Ob/ob mice were injected IP with specific GHS-R1α antagonist, and thereafter germ cell apoptosis and steroidogenic capability were assessed by TUNEL assay, (q) RT-PCR, and radioimmunoassay. RESULT(S): Expression of GHS-R1α and its endogenous ligand ghrelin was both up-regulated in ob/ob testis. Inhibition of the ghrelin pathway restored androgen synthesis, reduced germ cell apoptosis, and thereby resulted in improved sperm production in ob/ob mice. CONCLUSION(S): Ghrelin, as an antagonistic partner of leptin in the endocrinic/paracrine circuit, may be involved in the pathogenesis of male factor infertility induced by leptin deficiency.