Dysregulated Bone Marrow Contributes to Glomerular Injury through Soluble Factors.

BACKGROUND Immune dysregulation and chronic inflammation have been implicated in the pathogenesis of CKD. Altered bone marrow hematopoiesis is commonly observed in CKD-associated conditions, such as diabetes, cardiovascular disease, and aging. However, the role of bone marrow dysfunction in CKD progression has not been thoroughly interrogated in humans. This study examines how inflammation-induced bone marrow alterations contribute to CKD progression. METHODS Bone marrow aspirates were obtained from 10 CKD patients (8 with FSGS, 6 of whom were kidney transplant recipients) and from healthy donors. Samples were analyzed using ELISA, multiplex cytokine assays, multicolor flow cytometry, and scRNA sequencing. To mimic CKD patient bone marrow alterations, in vitro myelopoiesis assays were conducted under TNFα exposure. Cellular and molecular changes were assessed via ATAC-seq, RNA-seq, metabolic assays, flow cytometry, and cytokine analysis. We tested the in vivo effect of TNFα blockade and co-injection of TNFα with IFNγ in mice. We also measured TNFα levels in three different mouse models of proteinuria and in suPAR-deficient mice. The impact of secreted factors from TNFα-driven, functionally altered myeloid cells on kidney function was evaluated using high-throughput immunofluorescence assays on cultured podocytes and filtration function assays in zebrafish. RESULTS Bone marrow from CKD patients exhibited elevated TNFα and suPAR levels, along with inflammatory transcriptomic profiles in monocytic cells. TNFα-driven myelopoiesis in vitro induced altered monocytic cells resembling those in CKD patients. These cells displayed increased metabolic activity, transcriptional and epigenetic reprogramming, and elevated secretion of proinflammatory cytokines and suPAR. In a cooperative manner, these secreted factors caused filtration dysfunction in zebrafish and led to cytoskeletal disarrangement in cultured podocytes. In mice, TNFα exposure during myelopoiesis resulted in increased suPAR levels and proteinuria. CONCLUSIONS TNFα-driven alterations in bone marrow monocytic cells contribute to glomerular dysfunction in CKD, suggesting bone marrow dysfunction as a central upstream driver of CKD.