The role of testicular peritubular cells in human testicular ageing
Endocrinology, Diabetology, Metabolism
Biogerontology and Geriatric Medicine
Final Report Abstract
Testicular peritubular cells are emerging as an important part of the paracrine network of the testis and the testicular stem cell niche in human and nonhuman primate testes. We have put forward the hypothesis that they age and thereby contribute to overall declining testicular function in man. Bearing in mind that humans are long-lived and cannot be readily compared with short-lived animal models, we also postulated that next to the study of HTPCs (i.e. the sole human testicular cells, which can be readily examined in culture), nonhuman primate testes and derived TPCs must be studied. 1. Our studies showed that senescent HTPCs are characterized by a number of morphological and functional alterations. Focused ion beam scanning electron microscopy (FIB/SEM) tomography and thus 3D reconstruction revealed a reduced mitochondrial network and a strongly increased lysosome population. The results coincide with the data of a parallel proteome analysis and indicate deranged proteostasis. The mRNA levels of typical contractility markers and growth factors, important for the SSC niche, were however not significantly altered. A secretome analysis identified elevated levels of macrophage migration inhibitory factor (MIF) suggesting “inflammaging” and dipeptidyl peptidase 4 (DPP4), which may play a role in spermatogenesis, as it is, for example, able to cleave CXCL12, a factor involved in stem cell propagation. While testicular DPP4 could not be examined in testes from old men, it was however seen in some human testes samples of men with impaired spermatogenesis, indicating that it may further represent a possible drug target beyond aging. 2. Mechanistic studies in HTPCs are being hampered by the heterogeneity of human samples (due to age, life style, medical history of men). We therefore established that nonhuman primate monkey testicular peritubular cells (MKTPCs) from the common marmoset monkey (Callithrix jacchus;; cells from six young adult animals (2 3 years) and found that these cells are indeed a suitable translational model for the study of HTPCs. We found that MKTPCs can be propagated in vitro for certain passages (up to 12), retain characteristic markers for testicular peritubular cells and their proteome strongly (correlation coefficient of 0.78) overlaps with the proteome of HTPCs. Therefore, they qualify as a true translational model. 3. As MKTPCs share a high degree of homology with HTPCs, but like their human counterparts age in vitro, replicative senescence detected in high passage numbers limits in-depth functional or mechanistic studies. Therefore, a stable cellular model was established. MKTPCs of a young adult animal were immortalized by piggyBac transposition of human telomerase (hTERT), i.e. without the expression of viral oncogenes. Immortalized MKTPCs (iMKTPCs) grew without discernable changes for more than 50 passages and proof of principle experiments indicate that they are a highly appropriate cellular model for the study of primate peritubular cells. 4. Further studies were performed and are currently being evaluated. Especially proteome studies of CJ testes and in vivo data for MKTPCs yielded highly interesting results. The data collectively highlight the importance of peritubular cells for the human testis, and provided information that may be of clinical relevance. The project also served to build a multi-lab research consortium with common interests. For example, a follow up-project was recently funded by DFG, in which Artur Mayerhofer, Rüdiger Behr and Thomas Fröhlich will continue the fruitful interactions and work with TPCs.
Publications
- Characterization of a non-human primate model for the study of testicular peritubular cells-comparison with human testicular peritubular cells. Mol Hum Reprod. 2018 Aug 1;;24(8):401-410
Schmid N, Stöckl JB, Flenkenthaler F, Dietrich KG, Schwarzer JU, Köhn FM, Drummer C, Fröhlich T, Arnold GJ, Behr R, Mayerhofer A
(See online at https://doi.org/10.1093/molehr/gay025) - Insights into replicative senescence of human testicular peritubular cells. Sci Rep. 2019 Oct 21;;9(1):15052
Schmid N, Flenkenthaler F, Stöckl JB, Dietrich KG, Köhn FM, Schwarzer JU, Kunz L, Luckner M, Wanner G, Arnold GJ, Fröhlich T, Mayerhofer A.
(See online at https://doi.org/10.1038/s41598-019-51380-w)
