Epithelial Cell Biology Research Center, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
Hum Reprod. 2012 Sep;27(9):2585-97. doi: 10.1093/humrep/des254. Epub 2012 Jul 9.
Does elevated temperature-induced cystic fibrosis transmembrane conductance regulator (CFTR) down-regulation in Sertoli cells in cryptorchid testis disrupt testicular tight junctions (TJs) through the nuclear factor kappa B (NF-κB)/cyclooxygenase-2 (COX-2)/prostaglandin E(2) (PGE(2)) pathway?
Our results suggest that CFTR may be involved in regulating testicular TJs and the blood-testis barrier (BTB) through its negative regulation of the NF-κB/COX-2/PGE(2) pathway in Sertoli cells, a defect of which may result in the spermatogenesis defect in cryptorchidism.
Cryptorchidism, or undescended testes, is known to result in defective spermatogenesis. Although an elevated testicular temperature is regarded as an important factor affecting spermatogenesis in cryptorchidism, the exact mechanism remains elusive. It is known that the expression of functional CFTR is temperature sensitive. Our previous study has demonstrated that CFTR negatively regulates NF-κB/COX-2/PGE(2) in bronchial epithelial cells. Disruption of TJs by COX-2/PGE(2) has been found in tumour cells.
Expression of CFTR, NF-κB, COX-2 and TJ proteins was examined in the testes of a surgical-induced cryptorchidism mouse model and a testicular hyperthermia mouse model, as well as in control or CFTR-inhibited/knocked down primary rat Sertoli cells. PGE(2) production was measured by ELISA. Sertoli cell barrier function was determined by transepethelial resistance (TER) measurements in rat Sertoli cell primary cultures. BTB integrity in the cryptorchidism model was monitored by examining tracker dye injected into seminiferous tubules.
Down-regulation of CFTR accompanied by activation of NF-κB, up-regulation of COX-2 and down-regulation of TJ proteins, including ZO-1 and occludin, was observed in a cryptorchidism mouse model. BTB leakage revealed impaired BTB integrity in cryptorchid testes, confirming the destruction of TJs. The inverse correlation of CFTR and COX-2 was further confirmed in a mouse testis hyperthermia model and CFTR knockout mouse model. Culturing primary Sertoli cells at 37°C, which mimics the pathological condition of cryptorchidism, led to a significant decrease in CFTR and increase in COX-2 expression and PGE(2) production compared with the culture at the physiological 32°C. Inhibition or knockdown of CFTR led to increased COX-2 but decreased ZO-1 and occludin expression in Sertoli cells, which could be mimicked by PGE(2), but reversed by NF-κB or COX-2 inhibitor, suggesting that the regulation of TJs by CFTR is mediated by a NF-κB/COX-2/PGE(2) pathway. Inhibition of CFTR or administration of PGE(2) significantly decreased Sertoli cell TER.
This study has tested only the CFTR/NF-κB/COX-2/PGE(2) pathway in mouse testes in vivo and in rat Sertoli cells in vitro, and thus, it has some limitations. Further investigations in other species, especially humans, are needed.
Our study may shed more light on one of the aspects of the complicated underlying mechanisms of defective spermatogenesis induced by cryptorchidism.
隐睾症睾丸中升高的温度诱导的囊性纤维化跨膜电导调节因子（CFTR）下调是否通过核因子 kappa B（NF-κB）/环氧化酶-2（COX-2）/前列腺素 E（PGE（2））途径破坏 Sertoli 细胞中的睾丸紧密连接（TJ）？
我们的结果表明，CFTR 可能通过其对 Sertoli 细胞中 NF-κB/COX-2/PGE（2）途径的负调节来参与调节睾丸 TJ 和血睾屏障（BTB），其缺陷可能导致隐睾症中的精子发生缺陷。
隐睾症或未降睾丸会导致精子发生缺陷。虽然升高的睾丸温度被认为是隐睾症中影响精子发生的重要因素，但确切的机制仍不清楚。已知功能性 CFTR 的表达对温度敏感。我们之前的研究表明，CFTR 负调节支气管上皮细胞中的 NF-κB/COX-2/PGE（2）。已经在肿瘤细胞中发现 COX-2/PGE（2）破坏 TJ。
在手术诱导的隐睾症小鼠模型和睾丸过热小鼠模型以及对照或 CFTR 抑制/敲低的原代大鼠 Sertoli 细胞中检查 CFTR、NF-κB、COX-2 和 TJ 蛋白的表达。通过 ELISA 测量 PGE（2）的产生。通过在大鼠 Sertoli 细胞原代培养物中测量跨上皮电阻（TER）来确定 Sertoli 细胞屏障功能。通过检查注入生精小管的示踪染料来监测隐睾症模型中的 BTB 完整性。
在隐睾症小鼠模型中观察到 CFTR 下调伴随着 NF-κB 的激活、COX-2 的上调和 TJ 蛋白（包括 ZO-1 和 occludin）的下调。隐睾症睾丸中的 BTB 渗漏显示 BTB 完整性受损，证实了 TJ 的破坏。在睾丸过热模型和 CFTR 敲除小鼠模型中进一步证实了 CFTR 和 COX-2 的反向相关性。将原代 Sertoli 细胞在 37°C 下培养，模拟隐睾症的病理状况，与在生理 32°C 下培养相比，CFTR 显著减少，COX-2 表达和 PGE（2）产生增加。CFTR 的抑制或敲低导致 Sertoli 细胞中 COX-2 增加而 ZO-1 和 occludin 表达减少，这可以被 PGE（2）模拟，但被 NF-κB 或 COX-2 抑制剂逆转，表明 CFTR 对 TJ 的调节是通过 NF-κB/COX-2/PGE（2）途径介导的。CFTR 的抑制或 PGE（2）的给药显著降低了 Sertoli 细胞的 TER。
本研究仅在体内小鼠睾丸和体外大鼠 Sertoli 细胞中测试了 CFTR/NF-κB/COX-2/PGE（2）途径，因此存在一些局限性。需要在其他物种（尤其是人类）中进行进一步研究。
我们的研究可能为隐睾症引起的精子发生缺陷的复杂潜在机制的一个方面提供更多的线索。
