Cleavage-Resistant TREM2 Receptor: A Novel Strategy to Boost Macrophage Efferocytosis in Inflammatory Disease

Study Background and Research Question

Efficient clearance of apoptotic cells—termed efferocytosis—is fundamental for maintaining tissue homeostasis and suppressing inflammation. Macrophages, acting as professional phagocytes, rely on the receptor TREM2 (Triggering Receptor Expressed on Myeloid cells 2) to recognize and engulf apoptotic material. However, during inflammation, TREM2's signaling capacity is compromised because inflammatory mediators upregulate the metalloprotease ADAM17, which cleaves TREM2, disconnecting extracellular sensing from intracellular signaling. This disruption leads to impaired efferocytosis, accumulation of cell debris, and propagation of chronic inflammation. The central research question addressed by Dong et al. is whether engineering a TREM2 variant resistant to ADAM17-mediated cleavage can restore efferocytosis and thereby resolve inflammation in disease models.

Key Innovation from the Reference Study

The core breakthrough reported by Dong et al. (Cell Reports Medicine, 2026) is the design and validation of a synthetic, cleavage-resistant TREM2 (CRT) receptor. This engineered molecule fuses the native ligand-binding domain of TREM2 with its intracellular DAP12 signaling adaptor through a custom-designed stalk and transmembrane region. This architecture specifically prevents ADAM17 from cleaving the receptor, ensuring that TREM2 signaling persists even in inflammatory environments. By preserving receptor integrity, CRT enhances the capacity of macrophages to recognize and clear apoptotic cells, addressing a fundamental bottleneck in inflammation resolution mechanisms.

Methods and Experimental Design Insights

The study employed a multi-tiered strategy combining receptor engineering, lipid nanoparticle (LNP) technology, and in vivo disease modeling:

• Receptor Engineering: The CRT construct was synthesized by integrating the TREM2 extracellular domain, a tailored stalk sequence resistant to ADAM17 cleavage, and the DAP12 adaptor domain. Site-directed mutagenesis and structural modeling informed the stalk design to eliminate ADAM17 target motifs while maintaining membrane localization and signaling.
• mRNA Delivery Using LNPs: To generate CRT-expressing macrophages (CRT-Ms) in vivo, CRT-encoding mRNA was encapsulated in phosphatidylserine-functionalized LNPs. This targeted delivery system exploits macrophage recognition of phosphatidylserine, ensuring selective transfection.
• In Vitro Efferocytosis Assays: Macrophages expressing CRT were evaluated for their capacity to bind, engulf, and degrade apoptotic cells in culture, with comparison to wild-type and ADAM17-sensitive TREM2 controls.
• In Vivo Disease Models: Mouse models of metabolic-dysfunction-associated steatohepatitis (MASH) and atherosclerosis were used to assess the impact of in situ CRT-M generation on apoptotic cell clearance, inflammatory marker expression, and tissue pathology.

Protocol Parameters

• CRT mRNA LNP formulation: Use phosphatidylserine-functionalized LNPs for targeted macrophage delivery; optimize mRNA encapsulation efficiency and particle size for in vivo transfection.
• Macrophage efferocytosis assays: Incubate CRT-Ms with fluorescently labeled apoptotic cells; quantify engulfment via flow cytometry or confocal imaging.
• Inflammation models: For MASH, induce steatohepatitis using a high-fat, methionine- and choline-deficient diet; for atherosclerosis, use ApoE-deficient mice on a Western diet.
• Assessment of CRT integrity: Validate resistance to ADAM17 cleavage using Western blotting for full-length versus truncated receptor detection.

Core Findings and Why They Matter

Dong et al. demonstrated that the CRT receptor resists proteolytic cleavage by ADAM17, resulting in sustained TREM2-mediated intracellular signaling even during inflammation (see study). CRT-Ms exhibited enhanced efferocytosis capacity compared to wild-type macrophages, as evidenced by increased uptake of apoptotic cells in vitro. In mouse models, in situ delivery of CRT mRNA to macrophages significantly reduced the accumulation of apoptotic cells and lowered inflammatory cytokine levels. Importantly, CRT-M treatment ameliorated disease hallmarks in both MASH and atherosclerosis models, confirming the therapeutic potential of this approach for chronic inflammatory diseases driven by defective efferocytosis.

Comparison with Existing Internal Articles

Recent internal resources focus on optimizing fluorescent RNA probe synthesis and in vitro transcription workflows, especially for advanced gene expression and RNA–protein interaction studies. For example, the review of the HyperScribe T7 High Yield Cy5 RNA Labeling Kit highlights how efficient in vitro transcription RNA labeling supports sensitive detection in downstream applications. This dovetails with the Dong et al. protocol, where fluorescent nucleotide incorporation (e.g., Cy5-UTP) can facilitate quantitative tracking in efferocytosis assays and mRNA delivery validation. Another internal article describes precise strategies for fluorescent RNA probe synthesis, which could be adapted for labeling CRT mRNA or apoptotic cell tracers, enhancing assay sensitivity and reproducibility. Collectively, these resources provide complementary technical insights for researchers aiming to reproduce or extend CRT-mediated efferocytosis studies using robust RNA labeling and detection protocols.

Limitations and Transferability

While the engineered CRT receptor markedly improves efferocytosis and reduces inflammation in preclinical models, several limitations merit consideration. First, the long-term immunological consequences of sustained TREM2 signaling remain uncharacterized, particularly regarding off-target effects or potential macrophage reprogramming in chronic settings. Second, the LNP-mRNA delivery platform, though efficient in mice, may require further optimization for translation to human systems, where differences in lipid metabolism and immune recognition could affect targeting specificity and mRNA stability. Finally, although the study establishes proof-of-concept in MASH and atherosclerosis, the transferability of CRT-based strategies to other macrophage-driven diseases requires direct empirical validation.

Research Support Resources

For investigators seeking to implement similar workflows—such as mRNA transfection, in situ hybridization probe preparation, or detection of efferocytosis events—optimized labeling tools are essential. The HyperScribe™ T7 High Yield Cy5 RNA Labeling Kit (SKU K1062) provides a streamlined solution for generating Cy5-labeled RNA probes via T7 RNA polymerase-mediated in vitro transcription, supporting high-sensitivity detection in applications like Northern blot hybridization and fluorescence-tracked mRNA delivery. As detailed in several internal comparative analyses, this kit's tunable Cy5-UTP incorporation and robust workflow integration can help researchers achieve reproducible, quantitative results in efferocytosis and RNA delivery studies. Researchers interested in adapting CRT mRNA labeling for tracking or quantification purposes can benefit from these established protocols.