Human umbilical cord mesenchymal stem cell transplantation protects against reproductive damage induced by high-altitude hypoxia exposure in male mice

Abstract

BACKGROUND: High-altitude hypoxia has been reported to damage the male reproductive system, but whether stem cells can protect against male reproductive damage caused by high-altitude hypoxia has not been reported. OBJECTIVE: To investigate the preventive effect of human umbilical cord mesenchymal stem cell transplantation on reproductive damage in hypoxia-exposed male mice. METHODS: Human umbilical cord mesenchymal stem cells were isolated and cultured, and three-lineage differentiation and flow cytometry identification were performed. Twenty-one C57BL/6 male mice were randomly divided into control, hypoxia, and stem cell groups (n=7). The hypoxia and stem cell groups were exposed to a chronic intermittent hypoxia model simulating an altitude of 5,000 m (11.1% oxygen). In the stem cell group, 1×10^6 human umbilical cord mesenchymal stem cells were injected via the tail vein once a week for 6 weeks, while the other groups received PBS. Body mass, food intake, and water intake were monitored. After hypoxia exposure, testicular tissue was analyzed for morphology, ultrastructure, reactive oxygen species levels, and mitochondrial membrane potential; epididymal tissue was analyzed by hematoxylin-eosin staining and sperm motility; and the homing ability of stem cells was observed by DiL fluorescence tracing. RESULTS AND CONCLUSION: Human umbilical cord mesenchymal stem cell transplantation significantly improved water and food intake in hypoxic mice but had no significant effect on body mass. Morphological analysis showed that hypoxia caused edema of the testis and epididymis and shedding of spermatogenic cells, while stem cell transplantation alleviated these structural damages and reversed mitochondrial swelling and atrophy in germ cells. Additionally, stem cell transplantation significantly inhibited hypoxia-induced increase in reactive oxygen species, restored mitochondrial membrane potential, and improved sperm motility. Tracing experiments showed that after entering the mice, stem cells mainly accumulated in lung tissue, with low homing to the testis. In conclusion, human umbilical cord mesenchymal stem cell transplantation can protect the structure and function of germ cell mitochondria, reduce hypoxia-induced testicular and epididymal edema, and thereby restore spermatogenesis and sperm motility.

1. Introduction

Over the past few decades, global average sperm count and sperm concentration have declined by more than 50% [1-2]. Hypoxia is an important factor causing male reproductive damage. In addition to clinically common sleep apnea syndrome, the impact of high-altitude hypoxia on male reproduction has attracted widespread attention in recent years [3-4]. VERRATTI et al. [5] reported that healthy male mountaineers staying at high altitudes (2,000-5,600 m) for 26 days developed oligospermia, with reduced total motile sperm count and increased abnormal or immature sperm. Another study showed that after prolonged stays at high altitudes (5,100 m for 21-24 days; 6,700 m for 4-5 days), mountaineers experienced decreased sperm count, increased sperm abnormality rate, and decreased testosterone levels, which did not recover even 3 months after returning to plain areas [6]. LI et al. [7] found that hypoxia exposure reduced the number of undifferentiated spermatogonia in mice and significantly increased the proportion of abnormal sperm, indicating long-term damage to spermatogenesis. These studies demonstrate that high-altitude hypoxia severely affects male reproductive health.

Currently, drugs used to prevent or alleviate high-altitude damage mainly include synthetic chemicals and traditional Chinese medicines. In animal studies, chemical drugs such as pentoxifylline and erdosteine have shown protective effects against spermatogenic damage caused by high-altitude hypoxia [8-9], but these are primarily therapeutic drugs for other diseases, mainly used to alleviate altitude sickness, and have significant side effects. Traditional Chinese medicines have some efficacy, but their anti-hypoxia mechanisms are unclear and they are mostly used as health supplements [4]. Mesenchymal stem cells are a type of adult stem cells with multilineage differentiation potential, wide sources, high self-renewal, multilineage differentiation, low immunogenicity, immunomodulatory and tissue repair properties. Their safety and efficacy have been widely verified, and they have been used in various clinical applications.