Abstract
Tissue-resident macrophages (Mø) originating from fetal precursors are maintained via self-renewal under tissue-/organ-specific microenvironments. Herein, we developed a propagation method of testicular tissue-resident Mø in mixed primary culture with interstitial cells composed of Leydig cells from the mouse testis. We examined Mø/monocyte marker expression in propagated testicular Mø using flow cytometry; gene expression involved in testosterone production as well as spermatogenesis in testicular Mø and interstitial cells propagated by mixed culture via RT-PCR; and progesterone (P4) de novo production in propagated testicular Mø treated with cyclic adenosine monophosphate, isoproterenol, and M1 polarization inducers using ELISA. Mø marker expression patterns in the propagated Mø were identical to those in testicular interstitial Mø with a CD206-positive/major histocompatibility complex (MHC) II-negative M2 phenotype. We identified the genes involved in P4 production, transcription factors essential for steroidogenesis, and androgen receptors, and showed that P4 production de novo was upregulated by cyclic adenosine monophosphate and β2-adrenergic stimulation and was downregulated by M1 polarization stimulation in Mø. We also demonstrated the formation of gap junctions between Leydig cells and interstitial Mø. This is the first study to demonstrate de novo P4 production in tissue-resident Mø. Based on previous studies revealing inhibition of testosterone production by P4, we propose that local feedback machinery between Leydig cells and adjacent interstitial Mø regulates testosterone production. The results presented in this study can facilitate future studies on immune-endocrine interactions in gonads that are related to infertility and hormonal disorders.
Highlights
There are two types of macrophages (Mø) in adults: tissue-resident Mø, which colonize tissues/organs at a steady state and perform tissue-/organ-specific functions to maintain tissue/organ homeostasis, and recruited Mø, which originate from bone marrow-derived blood monocytes that infiltrate lesions in response to tissue/organ damage
We again hypothesized that testicular interstitial Mø adjacent to Leydig cells can produce sex steroids de novo. We evaluated this hypothesis by attempting to propagate testicular Mø in mixed culture with interstitial cells substantially composed of Leydig cells, assumed to be nicheforming cells, and further examined the presence of de novo sex steroid production in the propagated Mø
Testicular tissue-resident Mø were propagated by mixed culture with interstitial cells from mouse testis
Summary
There are two types of macrophages (Mø) in adults: tissue-resident Mø, which colonize tissues/organs at a steady state and perform tissue-/organ-specific functions to maintain tissue/organ homeostasis, and recruited Mø, which originate from bone marrow-derived blood monocytes that infiltrate lesions in response to tissue/organ damage. Based on recent evidence derived mainly from mice and partly from humans, most adult tissue-resident Mø have been shown to originate from fetal precursors in the yolk sac and/or fetal liver, which migrate to different tissues/organs during embryonic development, colonize tissue-/organspecific microenvironments (niches), and undergo tissue-/organ-specific differentiation into tissue-resident Mø [1]. Biomedicines 2022, 10, 487 that colonize interstitial tissues of different organs, such as the intestines and dermis, but do not proliferate locally in the colonizing tissues at a steady state. They are known to be gradually replaced by blood monocyte-derived Mø in mice [4,5]. This method can be applied to mouse tissueresident Mø from the liver, spleen, lung, and brain [8]
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