| Abstract |
Testicular macrophages (TM) are critical for the function of the testis by regulating homeostasis and inflammatory responses. However, the mechanisms by which TM fulfil these roles remain elusive. In this study, we explored the impact of two key testicular microenvironmental factors, namely 25-hydroxycholesterol (25HC), an oxysterol related to sex hormones and macrophage colony-stimulating factor (M-CSF), a factor crucial for macrophage survival and differentiation, on the regulation of the TM phenotype. Specifically, we examined their role in controlling the expression of the transcription factor interferon regulatory factor 7 (Irf7), a factor critical for maintaining the alternative macrophage phenotype. To achieve this, we used an in vitro bone marrow-derived macrophage (BMDM) model as a surrogate for TM to investigate the roles of 25HC and M-CSF in regulating the expression of Irf7 during the polarization of murine TM. M-CSF was identified as the main regulator of Irf7 expression, while 25HC production is a consequence of Irf7 activation in BMDM. In turn, 25HC plays a role in a negative feedback loop on the expression levels of Irf7 in BMDM. Using flow cytometry in Irf7-/- mouse testis the CD64loMHChi TM subpopulation was found to be decreased. Together with lower IL-10 protein levels in Irf7-/- TM this indicates a shift towards an M1-like macrophage profile. In summary, our data indicates that M-CSF could act as an inducer of high Irf7 expression levels in the mouse testis. However, the exact role of the high 25HC concentration in the testis in maintaining the local immune milieu still needs further study.
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