Paracrine Mechanisms of Histoplasma-Infected BM-MSCs Alter Signaling, Proliferation, and Viability of HSPCs

Stem cells possess regenerative and immunomodulatory capabilities; however, their role can be paradoxical during infections that alter hematopoiesis. Disseminated histoplasmosis is clinically associated with anemia and pancytopenia. Previous studies have shown that Histoplasma capsulatum can internalize and alter the function of mesenchymal stromal cells (MSCs) and hematopoietic stem cells and their progenitors (HSPCs). This study aimed to determine whether infection of BM-MSCs with H. capsulatum modulates HSPC viability, proliferation, and signaling through paracrine mechanisms. MSCs and HSPCs were isolated from the bone marrow of C57BL/6 mice. MSCs were infected with H. capsulatum yeast and subsequently co-cultured with HSPCs using transwell plates; additionally, HSPCs were treated with supernatants from infected MSCs. HSPCs were analyzed by flow cytometry to assess apoptosis, necrosis, and proliferation. Relative expression of genes related to Notch signaling was quantified by RT-qPCR. HSPCs cultured with conditioned medium or H. capsulatum-infected MSCs showed significantly increased apoptosis and necrosis, accompanied by reduced proliferation. Additionally, NOTCH1, NOTCH2, and JAGGED1 expression increased, whereas BCL2 expression decreased. These findings indicate that H. capsulatum-infected MSCs alter signaling pathways and cell fate in HSPCs through a paracrine mechanism.