Trem2/Dap12/Syk/PI3K axis contributes to the protection against cryptorchidism outcomes via modulating testicular macrophages

Description

Reduced hormone insulin-like 3 (Insl3), exclusively secreted by Leydig cells, has been identified as a recognized mechanism of cryptorchidism. Testicular macrophages residing in the testicular interstitium were thought to play a vital role on promoting Leydig cell hormone secretion, but their exact role in cryptorchidism remained poorly understood. Here, through RNA-seq analysis of normal and human cryptorchidism testes, triggering receptor expressed on myeloid cell-2 (Trem2) could be recognized as the most significant macrophage marker gene involved in human cryptorchidism, with Trem2-/- mouse testes at embryonic day 16.5 (E16.5) showing reduced Insl3 levels, leading to approximately 60% cryptorchidism mice. In our investigation into the underlying cause, utilizing an in vitro co-culture system, we found that Trem2-silenced macrophages impaired the proliferative capacity of Testicular macrophages acquired a distinctive transcriptional profile in unique cytoplasmic cross-fingering interactions with Leydig cells, primarily mediated by the Trem2-DNAX activation protein 12 (Dap12) receptor complex, which transduces intracellular signals via the spleen tyrosine kinase (Syk) and phosphoinositide 3-kinase (PI3K). Mechanistically, we found a reduction in the level of transforming growth factor-β (TGF-β), accompanied by elevated levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in RAW264.7 cells by ketoconazole (KET) treatment. Additionally, we found a positive correlation between Trem2 and Insl3 expression in a human ex vivo tissue culture model. In summary, our study proposes Trem2 as a novel target for maintaining normal testicular descent by regulating the testicular immune microenvironment.

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Reduced hormone insulin-like 3 (Insl3), exclusively secreted by Leydig cells, has been identified as a recognized mechanism of cryptorchidism. Testicular macrophages residing in the testicular interstitium were thought to play a vital role on promoting Leydig cell hormone secretion, but their exact role in cryptorchidism remained poorly understood. Here, through RNA-seq analysis of normal and human cryptorchidism testes, triggering receptor expressed on myeloid cell-2 (Trem2) could be recognized as the most significant macrophage marker gene involved in human cryptorchidism, with Trem2-/- mouse testes at embryonic day 16.5 (E16.5) showing reduced Insl3 levels, leading to approximately 60% cryptorchidism mice. In our investigation into the underlying cause, utilizing an in vitro co-culture system, we found that Trem2-silenced macrophages impaired the proliferative capacity of Testicular macrophages acquired a distinctive transcriptional profile in unique cytoplasmic cross-fingering interactions with Leydig cells, primarily mediated by the Trem2-DNAX activation protein 12 (Dap12) receptor complex, which transduces intracellular signals via the spleen tyrosine kinase (Syk) and phosphoinositide 3-kinase (PI3K). Mechanistically, we found a reduction in the level of transforming growth factor-β (TGF-β), accompanied by elevated levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in RAW264.7 cells by ketoconazole (KET) treatment. Additionally, we found a positive correlation between Trem2 and Insl3 expression in a human ex vivo tissue culture model. In summary, our study proposes Trem2 as a novel target for maintaining normal testicular descent by regulating the testicular immune microenvironment.

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