Impaired Function of the Blood-Testis Barrier during Aging Is Preceded by a Decline in Cell Adhesion Proteins and GTPases

Abstract

With increasing age comes many changes in the testis, including germ cell loss. Cell junctions in the testis tether both seminiferous epithelial and germ cells together and assist in the formation of the blood-testis barrier (BTB), which limits transport of biomolecules, ions and electrolytes from the basal to the adluminal compartment and protects post-meiotic germ cells. We hypothesize that as male rats age the proteins involved in forming the junctions decrease and that this alters the ability of the BTB to protect the germ cells. Pachytene spermatocytes were isolated from Brown Norway rat testes at 4 (young) and 18 (aged) months of age using STA-PUT velocity sedimentation technique. RNA was extracted and gene expression was assessed using Affymetrix rat 230 2.0 whole rat genome microarrays. Microarray data were confirmed by q-RT-PCR and protein expression by Western blotting. Of the genes that were significantly decreased by at least 1.5 fold, 70 were involved in cell adhesion; of these, at least 20 are known to be specifically involved in junction dynamics within the seminiferous epithelium. The mRNA and protein levels of Jam2, Ocln, cdh2 (N-cadherin), ctnna (α-catenin), and cldn11 (involved in adherens junctions), among others, were decreased by approximately 50% in aged spermatocytes. In addition, the GTPases Rac1 and cdc42, involved in the recruitment of cadherins to the adherens junctions, were similarly decreased. It is therefore not surprising that with lower expression of these proteins that the BTB becomes diminished with age. We saw, using a FITC tracer, a gradual collapse of the BTB between 18 and 24 months. This provides the opportunity for harmful substances and immune cells to cross the BTB and cause the disruption of spermatogenesis that is observed with increasing age.

AKAP9, a Regulator of Microtubule Dynamics, Contributes to Blood-Testis Barrier Function

“…However, the mice exhibited a significant number of patchy FITC-inulin deposits within the tubules that further increased in 42-dpp animals ( Figure 6C), indicating a breach of the BTB. The patchy distribution is similar to that observed by traditional analysis of FITC-inulin in tissue cross sections 47,48 whereas the more uniform FITC-inulin staining observed in the Akap9 KO ( Figure 6A) may be due to more robust leakage in these animals. Unlike the histologic analysis of FITC-inulin, the IVM approach may be able to distinguish between different levels of leakiness because there is no loss of the diffusible FITCinulin during sectioning and tissue preparation and because IVM permits observation of greater tissue volume than tissue sections.…”

The Gut Microbiota and Developmental Programming of the Testis in Mice

“…The levels of a trans-membrane component of the adherens junction complex, E-cadherin, was also reduced in GF mice, whereas the levels of an adaptor protein involved in intracellular signal transduction, β-catenin, was unaffected in testis tissue specimens obtained from GF mice. An age-related reduction of the components of adherens junctions (mRNA and protein) in aging mice was recently described by Paul and Robaire [37] . Furthermore, this demise of the BTB was associated with an increased permeability for a FITC tracer between the ages of 18 to 24 months.…”

Spermatotoxic Effects of Single-Walled and Multi-Walled Carbon Nanotubes on Male Mice

“…Oxidative stress (OS) and mitochondrial dysfunctionality seem to be the primary mechanisms in inducing CNT toxicity in the reproductive system. Testicular germ cells are protected via BTB (75). Bai et al (45) showed that continuous intravenous (i.v) injection of CNTs to BALB/c mice resulted in reversible injury to the testes due to testicular CNT accumulation and OS, even though fertility was not affected by CNT treatment.…”