Synthetic Cleavage-Resistant TREM2 Enhances Macrophage Efferocytosis

Study Background and Research Question

Efficient clearance of apoptotic cells by macrophages, a process termed efferocytosis, is essential for tissue homeostasis and the resolution of inflammation. The cell surface receptor TREM2 (Triggering Receptor Expressed on Myeloid cells 2) plays a central role in recognizing cell debris and activating downstream phagocytic signaling pathways. However, under inflammatory conditions, the sheddase ADAM17 is upregulated, resulting in proteolytic cleavage of TREM2, loss of its function, and accumulation of apoptotic cells. This loss of efferocytosis capability can contribute to chronic inflammatory diseases, such as metabolic-dysfunction-associated steatohepatitis (MASH) and atherosclerosis. The research by Dong et al. sought to address whether engineering a TREM2 variant resistant to cleavage could restore efferocytosis and ameliorate inflammation (Dong et al., 2026).

Key Innovation from the Reference Study

The central innovation in this study is the design and validation of a synthetic cleavage-resistant TREM2 receptor (CRT). CRT integrates the extracellular ligand-binding domain of TREM2 with its intracellular signaling adaptor DAP12 via a custom-engineered stalk and transmembrane region, thereby preventing ADAM17-mediated proteolysis. This design ensures persistent signaling even in highly inflammatory environments where wild-type TREM2 would be shed from the cell surface. Importantly, the authors developed a lipid nanoparticle (LNP) system functionalized with phosphatidylserine, allowing for macrophage-selective delivery of CRT mRNA and efficient in situ generation of CRT-expressing macrophages (CRT-Ms) within affected tissues.

Methods and Experimental Design Insights

To achieve robust CRT expression in macrophages, the authors constructed synthetic mRNA encoding the cleavage-resistant receptor. This mRNA was packaged into phosphatidylserine-functionalized LNPs, exploiting the natural affinity of macrophages for phosphatidylserine. Key protocol parameters included the optimization of mRNA dosage for efficient transfection, verification of CRT expression and surface localization, and assessment of resistance to ADAM17-mediated cleavage using biochemical assays.

Protocol Parameters

• CRT mRNA delivery: Phosphatidylserine-LNPs were used for selective targeting of macrophages in vivo.
• Inflammatory challenge: Mouse models of MASH and atherosclerosis were established to evaluate in vivo efficacy of CRT-Ms.
• Assessment of receptor cleavage: ADAM17 levels and CRT integrity were determined by immunoblotting and flow cytometry post-treatment.
• Efferocytosis evaluation: Phagocytic uptake of labeled apoptotic cells was tracked using fluorescent microscopy and quantification assays.
• Tissue inflammation markers: Reduction in pro-inflammatory cytokines was measured by ELISA and qPCR in target organs.

Core Findings and Why They Matter

The study demonstrated that macrophages expressing CRT retain surface receptor expression and robustly amplify intracellular TREM2 signaling even in the presence of enhanced ADAM17 activity. CRT-Ms showed significantly improved clearance of apoptotic cells in both in vitro and in vivo settings. In mouse models of MASH and atherosclerosis, in situ generation of CRT-Ms led to a marked decrease in apoptotic cell burden and a significant reduction in inflammatory cytokine expression. These findings confirm that overcoming TREM2 cleavage is a viable strategy to restore macrophage efferocytosis and potentially reverse pathological inflammation (Dong et al., 2026).

From a mechanistic perspective, the CRT design not only prevents proteolytic shedding but also enhances the activation of DAP12-dependent signaling pathways, which are critical for phagocytic function and immune resolution. This positions CRT as a unique tool to dissect the molecular underpinnings of efferocytosis and its therapeutic modulation.

Comparison with Existing Internal Articles

Recent internal articles have highlighted methodological advances in RNA probe synthesis, fluorescent labeling, and probe delivery for in situ molecular studies. For example, "HyperScribe™ T7 High Yield Cy5 RNA Labeling Kit: Pushing..." discusses how advanced Cy5 RNA labeling enables customizable, high-sensitivity fluorescent probe generation for applications such as in situ hybridization and efferocytosis research. Similarly, "HyperScribe™ T7 High Yield Cy5 RNA Labeling Kit in Advanced mRNA Probe Design" connects customizable Cy5 RNA probe synthesis to evolving needs in targeted RNA delivery and detection.

While these internal resources focus primarily on probe synthesis for molecular detection, the CRT study represents a direct intervention at the protein and signaling level, using mRNA-LNPs to modulate cellular effector functions within disease models. The linking point is that both approaches depend on high-fidelity mRNA production, robust in vitro transcription, and sensitive detection of RNA or protein products—critical for both mechanistic studies and translational applications.

Limitations and Transferability

Several considerations temper the translational potential of the CRT strategy. First, while the LNP-mRNA system is highly efficient for macrophage targeting in murine models, its performance, safety, and immunogenicity in human tissues remain to be fully established. The long-term persistence and functional stability of CRT-Ms in chronic disease settings also require further study. Additionally, the approach is tailored specifically to ADAM17-mediated TREM2 cleavage and may not generalize to other inflammatory or degenerative contexts where different regulatory mechanisms are at play.

Despite these limitations, the CRT platform offers a modular foundation for engineering protease-resistant receptors or signaling adapters in diverse cell types, suggesting broader applicability in immune modulation and disease intervention, pending further validation.

Research Support Resources

For researchers aiming to study macrophage efferocytosis, ADAM17-mediated receptor shedding, or to develop fluorescent probes for in situ hybridization and Northern blot hybridization applications, high-quality RNA labeling tools are essential. The HyperScribe™ T7 High Yield Cy5 RNA Labeling Kit (SKU K1062) provides a reliable platform for the synthesis of randomly Cy5-labeled RNA probes using T7 RNA polymerase transcription and Cy5-UTP incorporation. This kit supports customizable fluorescent nucleotide incorporation, enabling sensitive detection of RNA in advanced assays, and complements workflows described in both the CRT study and recent probe development articles. For highly demanding applications, an upgraded version with even greater RNA yield is also available from APExBIO.