Trimethylamine N-oxide promotes lymphoid differentiation of hematopoietic stem and progenitor cells

Background Persistent lymphopenia represents a clinically relevant adverse effect associated with radiotherapy, surgery and infection and is linked to unfavorable clinical outcomes. Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite generated from dietary choline and L -carnitine, has emerged as a potential regulator of host physiology; however, its role in lymphoid differentiation remains unclear. Methods c-Kit⁺ hematopoietic stem and progenitor cells (HSPCs) were isolated from mouse bone marrow using immunomagnetic beads and subjected to an in vitro lymphoid differentiation assay. Normal and irradiated C57BL/6 mice were treated with L -carnitine by gavage, a high-choline diet, or TMAO-containing drinking water. Serum TMAO concentrations were measured by LC-MS/MS. Lymphoid populations in the bone marrow, spleen, and peripheral blood were analyzed by flow cytometry and routine blood tests, and the underlying mechanism was examined using pharmacological inhibition, qPCR, and Western blotting. Results TMAO promoted the lymphoid differentiation of mouse c-Kit⁺ HSPCs in vitro. Mice treated with L -carnitine by gavage, a high-choline diet, or TMAO-containing drinking water had increased serum TMAO levels. These TMAO-elevating interventions increased the lymphoid cell proportions in the bone marrow, spleen, and peripheral blood and increased the HSPC population. This lymphoid-promoting effect was further evident in irradiated mice, in which TMAO accelerated lymphoid recovery. Mechanistically, TMAO activated its receptor, PERK, leading to increased PERK phosphorylation and subsequent upregulation of HOXA9/Pim-1 signaling, whereas inhibition of PERK or HOXA9 attenuated the lymphoid-promoting effect of TMAO. Conclusions Our findings reveal a previously unrecognized role of TMAO in promoting HSPC lymphoid differentiation through activation of the PERK–HOXA9/Pim-1 signaling axis, providing new insights into potential strategies for managing lymphopenia.