HYPERCHOLESTEROLEMIA INDUCES TRAINED IMMUNITY THAT EXACERBATES KIDNEY INFLAMMATION AND FIBROSIS

Although hypercholesterolemia is a significant risk factor for chronic kidney disease, clinical lipid-lowering therapies have failed to effectively slow the progression of renal dysfunction, suggesting limitations in the conventional "lipotoxicity" theory. Some studies have found that residual inflammatory risk is a stronger predictor of recurrent cardiovascular events than residual cholesterol risk, revealing that hypercholesterolemia may involve more complex immune regulatory mechanisms. Recent breakthroughs in immunometabolism have demonstrated that metabolic disorders—such as hyperlipidemia and hyperglycemia—can train myeloid cells. Even after metabolic parameters normalize, these trained cells exhibit a sustained pro-inflammatory phenotype and release more inflammatory cytokines upon stimulation compared to untrained cells, a phenomenon known as "trained immunity." Based on this, we hypothesize that hypercholesterolemia may promote renal fibrosis by inducing trained immunity in myeloid cells.

We established a hypercholesterolemia mouse model induced by a high-fat diet (HFD). After switching back to a regular diet (RD), the mice underwent unilateral renal ischemia-reperfusion injury (uIRI) to model kidney damage. Renal fibrosis was assessed by Western blotting and Picrosirius Red staining, while renal inflammation was evaluated via flow cytometry and qPCR. Bone marrow transplantation experiments and studies using Rag1⁻/⁻ mice were conducted to clarify the role of trained immunity in myeloid cells. Single-cell RNA sequencing (scRNA-seq), Assay for Transposase-Accessible Chromatin with sequencing (ATAC-seq), and Cleavage Under Targets & Tagmentation (CUT&TAG) were further employed to investigate the molecular mechanisms through which trained immunity exacerbates chronic kidney disease. 

The results showed that HFD-RD mice exhibited significantly higher levels of renal fibrosis after uIRI compared to CD-RD mice, along with increased infiltration of neutrophils and macrophages in both peripheral blood and kidney tissue. Myeloid cells (macrophages and neutrophils) from HFD-RD mice secreted higher levels of the pro-inflammatory cytokine TNFα. Moreover, bone marrow hematopoietic stem cells showed biased differentiation toward granulocyte-monocyte progenitors. We isolated myeloid cells from the kidneys of competitive bone marrow chimeric mice and performed scRNA-seq sequencing. Analysis revealed an expansion of CRIP1-hi macrophages in the kidneys of HFD-fed mice compared to CD controls. This CRIP1-hi subpopulation exhibited enhanced Crip1 gene expression, strong infiltrative capacity, and heightened inflammatory response and glycolytic activity. Moreover, CRIP1-hi cells from HFD mice showed higher expression of genes related to these signaling pathways compared to those from CD mice. Renal pelvic injection of si-Crip1 downregulated the protein levels of α-SMA and FN in HFD-RD mice following uIRI, accompanied by reduced TNFα/IL-1β expression in renal macrophages and decreased neutrophil infiltration. 

These findings demonstrate that hypercholesterolemia mediates a form of central trained immunity in the bone marrow, endowing descendant myeloid cells with a trained immunophenotype. These primed cells exacerbate inflammation and fibrosis upon subsequent injury. Crip1 is identified as a key effector gene in hypercholesterolemia-induced trained immunity. Its upregulation is closely associated with enhanced glycolytic reprogramming and pro-inflammatory functions in myeloid cells, and it plays a significant role in promoting renal fibrosis under hypercholesterolemic conditions.