Apoptotic Vesicular Metabolism Contributes to Organelle Assembly and Safeguards Liver Homeostasis and Regeneration.

BACKGROUND & AIMS: Apoptosis generates plenty of membrane-bound nanovesicles, the apoptotic vesicles (apoVs), which show promise for biomedical applications. The liver serves as a significant organ for apoptotic material removal. Whether and how the liver metabolizes apoptotic vesicular products and contributes to liver health and disease is unrecognized. METHODS: apoVs were labeled and traced after intravenous infusion. Apoptosis-deficient mice by Fas mutant (Fasmut) and Caspase-3 knockout (Casp3-/-) were used with apoV replenishment to evaluate the physiological apoV function. Combinations of morphologic, biochemical, cellular, and molecular assays were applied to assess the liver while hepatocyte analysis was performed. Partial hepatectomy and acetaminophen liver failure models were established to investigate liver regeneration and disease recovery. RESULTS: We discovered that the liver is a major metabolic organ of circulatory apoVs, in which apoVs undergo endocytosis by hepatocytes via a sugar recognition system. Moreover, apoVs play an indispensable role to counteract hepatocellular injury and liver impairment in apoptosis-deficient mice upon replenishment. Surprisingly, apoVs form a chimeric organelle complex with the hepatocyte Golgi apparatus through the soluble N-ethylmaleimide-sensitive factor attachment protein receptor machinery, which preserves Golgi integrity, promotes microtubule acetylation by regulating α-tubulin N-acetyltransferase 1, and consequently facilitates hepatocyte cytokinesis for liver recovery. The assembly of the apoV-Golgi complex is further revealed to contribute to liver homeostasis, regeneration, and protection against acute liver failure. CONCLUSIONS: These findings establish a previously unrecognized functional and mechanistic framework that apoptosis through vesicular metabolism safeguards liver homeostasis and regeneration, which holds promise for hepatic disease therapeutics.

Apoptosis releases hydrogen sulfide to inhibit Th17 cell differentiation.

Over 50 billion cells undergo apoptosis each day in an adult human to maintain immune homeostasis. Hydrogen sulfide (H2S) is also required to safeguard the function of immune response. However, it is unknown whether apoptosis regulates H2S production. Here, we show that apoptosis-deficient MRL/lpr (B6.MRL-Faslpr/J) and Bim-/- (B6.129S1-Bcl2l11tm1.1Ast/J) mice exhibit significantly reduced H2S levels along with aberrant differentiation of Th17 cells, which can be rescued by the additional H2S. Moreover, apoptotic cells and vesicles (apoVs) express key H2S-generating enzymes and generate a significant amount of H2S, indicating that apoptotic metabolism is an important source of H2S. Mechanistically, H2S sulfhydrates selenoprotein F (Sep15) to promote signal transducer and activator of transcription 1 (STAT1) phosphorylation and suppress STAT3 phosphorylation, leading to the inhibition of Th17 cell differentiation. Taken together, this study reveals a previously unknown role of apoptosis in maintaining H2S homeostasis and the unique role of H2S in regulating Th17 cell differentiation via sulfhydration of Sep15C38.

Apoptotic vesicles are required to repair DNA damage and suppress premature cellular senescence.

It is well known that DNA damage can cause apoptosis. However, whether apoptosis and its metabolites contribute to DNA repair is largely unknown. In this study, we found that apoptosis-deficient Fasmut and Bim- /- mice show significantly elevated DNA damage and premature cellular senescence, along with a significantly reduced number of 16,000 g apoptotic vesicles (apoVs). Intravenous infusion of mesenchymal stromal cell (MSC)-derived 16,000 g apoVs rescued the DNA damage and premature senescence in Fasmut and Bim-/- mice. Moreover, a sublethal dose of radiation exposure caused more severe DNA damage, reduced survival rate, and loss of body weight in Fasmut mice than in wild-type mice, which can be recovered by the infusion of MSC-apoVs. Mechanistically, we showed that apoptosis can assemble multiple nuclear DNA repair enzymes, such as the full-length PARP1, into 16,000 g apoVs. These DNA repair components are directly transferred by 16,000 g apoVs to recipient cells, leading to the rescue of DNA damage and elimination of senescent cells. Finally, we showed that embryonic stem cell-derived 16,000 g apoVs have superior DNA repair capacity due to containing a high level of nuclear DNA repair enzymes to rescue lethal dose-irradiated mice. This study uncovers a previously unknown role of 16,000 g apoVs in safeguarding tissues from DNA damage and demonstrates a strategy for using stem cell-derived apoVs to ameliorate irradiation-induced DNA damage.