Mesenchymal stem cell-derived apoptotic vesicles alleviate Acetaminophen-induced acute liver failure by inhibiting PANoptosis via miR-378a-5p/NLRC5 axis

Technical Summary: Mesenchymal Stem Cell-Derived Apoptotic Vesicles Alleviate Acetaminophen-Induced Acute Liver Failure by Inhibiting PANoptosis via miR-378a-5p/NLRC5 Axis

Problem Statement
Acetaminophen (APAP) overdose is the leading cause of drug-induced acute liver failure (ALF) globally. While N-acetylcysteine (NAC) is the standard treatment, it is only effective within a critical 10-hour window; patients presenting after this period face poor outcomes, with liver transplantation remaining the only definitive rescue for severe cases. The pathological mechanism of APAP-ALF involves mitochondrial dysfunction, oxidative stress, and extensive hepatocyte death. Recent evidence suggests that APAP induces multiple forms of programmed cell death (apoptosis, pyroptosis, and necroptosis) simultaneously. However, the systematic correlation between these death pathways and whether they converge into a unified mechanism known as PANoptosis in APAP-ALF remains unclear. Furthermore, while Mesenchymal Stem Cells (MSCs) and their extracellular vesicles show therapeutic potential, the specific regulatory role of MSC-derived apoptotic vesicles (MSC-ApoVs) in modulating PANoptosis in APAP-ALF has not been defined.

Methodology
The study employed a multi-faceted approach combining in vivo and in vitro models with molecular biology techniques:

• Models: An APAP-induced acute liver failure mouse model (C57BL/6, 600 mg/kg APAP) and hepatocyte injury models using Huh7 and AML12 cell lines.
• Intervention: MSC-ApoVs were isolated from human umbilical cord MSCs induced to undergo apoptosis via staurosporine (STS). These vesicles were characterized via TEM, NTA, and flow cytometry.
• Engineering: MSCs were transfected with miR-378a-5p mimics or inhibitors to generate engineered MSC-ApoVs for gain-of-function and loss-of-function studies.
• Mechanistic Exploration:
  • Omics: Transcriptome sequencing (RNA-seq) and miRNA sequencing were performed to identify differentially expressed genes and miRNAs.
  • Molecular Validation: Luciferase reporter assays confirmed direct binding between miR-378a-5p and the 3'UTR of NLRC5. siRNA knockdown of NLRC5 was used to mimic the effects of MSC-ApoVs.
  • Cell Death Analysis: Techniques included TUNEL staining, PI staining, EdU assays, JC-1 and MitoSox staining for mitochondrial function, and Western blotting for markers of apoptosis (Caspase-3/7), pyroptosis (GSDMD/ME, Caspase-1), and necroptosis (p-MLKL).
  • PANoptosome Detection: Immunofluorescence co-localization of RIPK3, ASC, and Caspase-8 was used to visualize PANoptosome assembly.
  • Immune Profiling: Flow cytometry and Transwell assays assessed macrophage infiltration, T-cell proliferation, and chemotaxis.

Key Results

1. Therapeutic Efficacy of MSC-ApoVs: In vivo, MSC-ApoV treatment significantly reduced serum ALT/AST levels, decreased liver necrosis, and improved survival in APAP-induced mice. In vitro, MSC-ApoVs reversed APAP-induced loss of cell viability and proliferation.
2. Inhibition of Multiple Cell Death Pathways: MSC-ApoVs simultaneously suppressed markers of pyroptosis (GSDMD-N, GSDME-N, cleaved-Caspase-1), apoptosis (cleaved-Caspase-3/7), and necroptosis (p-MLKL). They also preserved mitochondrial membrane potential and reduced ROS levels.
3. Discovery of PANoptosis in APAP-ALF: The study identified the formation of the RIPK3-ASC-Caspase-8 PANoptosome complex in both APAP-treated mouse liver tissues and human drug-induced liver injury (DILI) samples. MSC-ApoVs treatment blocked the assembly of this complex.
4. Identification of the NLRC5/miR-378a-5p Axis:
   • RNA-seq identified NLRC5 (NOD-like receptor family CARD domain containing 5) as a key upregulated gene in APAP injury that was downregulated by MSC-ApoVs.
   • Knocking down NLRC5 in hepatocytes mimicked the protective effects of MSC-ApoVs, inhibiting PANoptosome formation and reducing inflammatory cytokine release.
   • miRNA sequencing revealed that MSC-ApoVs are enriched with miR-378a-5p. Luciferase assays confirmed that miR-378a-5p directly targets and inhibits NLRC5 mRNA.
5. Mechanism Confirmation: Engineering MSC-ApoVs to overexpress miR-378a-5p enhanced their ability to inhibit PANoptosis and liver injury, while inhibiting miR-378a-5p weakened these protective effects.
6. Immunomodulation: By blocking PANoptosis, MSC-ApoVs reduced the release of pro-inflammatory factors (TNF-α, IL-1β, IL-18) and chemokines, thereby inhibiting macrophage infiltration and abnormal T-cell activation in the liver.

Key Contributions

• First Demonstration of PANoptosis in APAP-ALF: The study provides the first evidence that APAP-induced hepatocyte death involves PANoptosis, driven by the assembly of a RIPK3-ASC-Caspase-8 complex, rather than isolated death pathways.
• Elucidation of MSC-ApoV Mechanism: It defines the specific molecular mechanism by which MSC-ApoVs exert therapeutic effects, identifying the "miR-378a-5p/NLRC5" axis as the critical regulator.
• Validation of NLRC5 as a Therapeutic Target: The research establishes NLRC5 as a key driver of PANoptosome assembly in hepatocytes and confirms that its inhibition is sufficient to block the inflammatory cascade.
• Cell-Free Therapy Strategy: The study validates engineered MSC-ApoVs as a potent, cell-free therapeutic strategy for treating APAP-ALF, particularly for patients who have missed the NAC treatment window.

Significance
This study reveals a novel mechanism for the treatment of acetaminophen-induced acute liver failure. By demonstrating that MSC-ApoVs deliver miR-378a-5p to hepatocytes to suppress NLRC5, thereby blocking PANoptosome assembly and the subsequent inflammatory storm, the authors propose a new cell-free therapeutic paradigm. This approach addresses the limitations of current treatments by targeting the upstream molecular drivers of multi-modal cell death and immune dysregulation, offering a potential rescue strategy for severe APAP-ALF cases where conventional therapies fail.