BLT Reagent Supports Crohn’s Disease Inflammation Research: Macrophage MERTK Restrains GRAMD1A-driven Mitochondrial Oxysteroltrafficking to Limit Colitis

New progress has been made in research on chronic intestinal inflammation in Crohn’s disease (CD).

Professor Xiuwen Wu’s team from Jinling Hospital, Nanjing University, in collaboration with researchers from the Affiliated BenQ Hospital of Nanjing Medical University and other institutions, published their findings in “Redox Biology” (IF = 11.9, Q1 journal).

This study reveals a critical pathogenic axis involving MERTK, GRAMD1A-mediated mitochondrial oxysterol transport, and TBK1 signaling, providing new insights into the immunometabolic mechanisms underlying chronic intestinal inflammation and the development of Crohn’s disease.

Defective efferocytosis by macrophages is a major driver of chronic inflammation in inflammatory bowel disease (IBD), yet the underlying immunometabolic regulatory mechanisms remain poorly understood. Clinical studies have demonstrated a close association between cholesterol metabolism disorders and the onset of CD. Abnormal cholesterol transport between the endoplasmic reticulum (ER) and mitochondria can impair mitochondrial function; however, whether oxysterol metabolic imbalance contributes to macrophage inflammatory activation and the key molecular networks involved remain unclear. As a macrophage-specific efferocytosis receptor, MERTK is significantly downregulated in the intestinal mucosa of patients with active CD, but its role in lipid metabolic reprogramming and colitis progression has not been fully elucidated.

The study found that MERTK⁺ macrophages were markedly reduced in the intestinal mucosa of patients with Crohn’s disease. MERTK deficiency did not affect classical macrophage polarization but instead impaired efferocytosis and activated the SREBP2 pathway, promoting de novo cholesterol synthesis in the ER. Through the MERTK-ITIM/SHP1/RNF123 ubiquitination axis, MERTK deficiency relieved the degradation of GRAMD1A, resulting in excessive ER-to-mitochondria cholesterol transport mediated by GRAMD1A. Excess mitochondrial cholesterol was subsequently metabolized by CYP27A1 into polyhydroxylated oxysterols such as 27-hydroxycholesterol (27-OHC), leading to mitochondrial respiratory chain dysfunction, excessive mitochondrial ROS production, and leakage of mtDNA and dsRNA. These events preferentially activated the RIG-I/MAVS-TBK1 signaling pathway, driving NF-κB- and IRF3-mediated intestinal hyperinflammation, epithelial barrier disruption, and gut microbiota dysbiosis. In vivo experiments further demonstrated that gut microbiota alterations were not the initiating factor in MERTK deficiency–aggravated colitis. Instead, myeloid cell–specific knockdown of GRAMD1A significantly alleviated acute and chronic colitis, mucosal injury, and fibrosis, confirming that the MERTK–GRAMD1A–mitochondrial oxysterol–TBK1 axis is a key pathogenic pathway in Crohn’s disease.

Experiments using Aniview

Mitochondrial damage can trigger the release of mtDNA and mtRNA, activating both the cGAS-STING and RIG-I/MAVS pathways, which converge on the downstream kinase TBK1. The study showed that MERTK-knockout macrophages were highly sensitive to the STING agonist DMXAA, indicating that TBK1 signaling was already in a pre-activated state. Transcriptomic analysis also revealed enrichment of inflammasome-related pathways. Furthermore, mitochondrial stress products such as lipid peroxides can activate the NLRP3 inflammasome and induce pyroptosis. Using the Mito DNA-targeting Tracker reagent developed by Guangzhou Biolight Biotechnology Co., Ltd., the authors observed substantial cytosolic release of mitochondrial mtDNA following MERTK inhibition, a hallmark feature of nucleic acid leakage caused by mitochondrial damage.

DOI: 10.1016/j.redox.2026.104174