Unveiling the Role of KSHV-Infected Human Mesenchymal Stem Cells in Kaposi's Sarcoma Initiation

Kaposi's sarcoma (KS) may derive from Kaposi's Sarcoma Herpesvirus (KSHV)-infected human Mesenchymal Stem Cells (hMSCs) that migrate to sites characterized by inflammation and angiogenesis, promoting the initiation of KS. By analyzing the RNA sequences of KSHV-infected primary hMSCs, we have identified specific cell subpopulations, mechanisms, and conditions involved in the initial stages of KSHV-induced transformation and reprogramming of hMSCs into KS progenitor cells. Under pro-angiogenic environmental conditions, KSHV can reprogram hMSCs to exhibit gene expression profiles more similar to KS tumors, activating cell cycle progression, cytokine signaling pathways, and endothelial differentiation indicating the involvement of KSHV infection in inducing the Mesenchymal-to-Endothelial (MEndT) transition of hMSCs. This finding underscores the significance of this condition in facilitating KSHV-induced proliferation and reprogramming of hMSCs towards MEndT and closer to KS gene expression profiles, providing further evidence of these cell subpopulations as precursors of KS cells that thrive in a pro-angiogenic environment. To evaluate the impact of different growth conditions in KSHV infection of bone marrow-derived human Mesenchymal Stem Cells (hMSC), we infected these cells with KSHV in different environments. We performed KSHV (KSHVr.219) infection of hMSC in MEM alpha medium, basal MSC growth conditions (MSC-KSHV MEM), or KS-like pro-angiogenic conditions (MSC-KSHV KS). After 72 hours of infection (short-term infection) or after one month of infection and selection for KSHV-infected cells (long-term infection), we extracted RNA to perform a whole RNA-sequencing analysis. As controls for both time points, we included mock-infected hMSCs growing under basal MSC growth conditions (MSC MEM) and mock-infected hMSCs growing in KS-like pro-angiogenic conditions (MSC KS) to study the effects of the pro-angiogenic environment.