Irisin-treated microbiota restore blood–testis barrier integrity and spermatogenesis in chronically stressed rats

Chronic psychological stress impairs male fertility by disrupting spermatogenesis and the blood-testis barrier (BTB), which is essential for testicular function. Irisin, a myokine/adipokine involved in metabolic regulation, protects against testicular dysfunction and may beneficially modulate gut microbiota, highlighting its potential in the gut–testis axis. This study investigated the effect of fecal microbiota transplantation (FMT) from irisin-treated rats in restoring BTB integrity in a chronic unpredictable stress (CUS) rat model. Male Sprague-Dawley rats were randomized into four groups: Control, CUS, CUS + Control-FMT, and CUS + Irisin-FMT. CUS-exposed rats received FMT (5 mL, intra-rectally, on alternate days for 2 weeks) from donors treated with either irisin (100 ng/kg, subcutaneously, 4 weeks) or vehicle. The CUS + Irisin-FMT group showed marked improvements in sperm quality, and hormonal profiles, including testosterone, LH, FSH, and irisin. Irisin-FMT increased crypt length, goblet cells, and histological scores, and improved the testicular histological structure and Johnsen’s index. These effects were accompanied by upregulation of BTB proteins, E- and N-cadherin, spermatogonia markers, suppression of inflammatory markers (NF-κB, IL-1β, IL-6), and activation of integrin–FAK/Akt/mTOR signaling. Microbiota analysis revealed an increase in beneficial genera, including Lactobacillus and Blautia, as well as the restoration of key families and phyla. Dysbiosis promotes systemic inflammation by altering butyrate and acetate, impairing BTB integrity and testicular function via immune activation, oxidative stress, and endocrine disruption. Irisin-FMT mitigates stress-induced testicular dysfunction by modulating gut microbiota and activating protective signaling pathways, highlighting a novel microbiome-based strategy for male infertility.