[The Effect of SIRT5 Deletion on Recovery of Hematopoietic Stem Cells after Injury in Mouse].

OBJECTIVE: To investigate the effect of deacylase Sirtuin 5 in the recovery of hematopoietic stem cells (HSCs) after treated by 5-FU in mouse. METHODS: Flow cytometry was used to analyze the effect of SIRT5 deletion on the proportion of hematopoietic stem/progenitor cells (HSPCs) in bone marrow (BM), the proportion of T cells, B cells and myeloid cells (TBM) in peripheral blood (PB) and spleen, and the development of T cells in thymus. Mouse were treated with 5-FU to study the effect of SIRT5 deletion on the cell cycle, apoptosis and the proportion of HSPCs in BM. The effect of SIRT5 deletion on the proliferation of HSCs was analyzed by flow sorting in vitro. RESULTS: SIRT5 deletion did not affect the development of T cells in thymus and the proportion of TBM cells in PB and spleen compared with wild type mice. SIRT5 deletion increased proportion of HSPCs in BM. After 5-FU treatment, the proportion of HSCs in SIRT5 deletion mice was significant decreased (P < 0.05), the HSPC in SIRT5 deletion mice was activated from G0 to G1 phase (P < 0.05), and the proportion of early apoptosis increased (P < 0.05). By monoclonal culture in vitro, the ability of HSCs to form clones in SIRT5 deletion mice was decreased significantly (P < 0.05). CONCLUSION: SIRT5 deletion lead to a decreased the ability of HSCs to clone in vitro. SIRT5 deletion is not conducive to the recovery of HSPCs injury in mice under hematopoietic stress.

mTORC2 Facilitates Liver Regeneration Through Sphingolipid-Induced PPAR-α-Fatty Acid Oxidation.

BACKGROUND & AIMS: During liver regeneration after partial hepatectomy, the function and metabolic pathways governing transient lipid droplet accumulation in hepatocytes remain obscure. Mammalian target of rapamycin 2 (mTORC2) facilitates de novo synthesis of hepatic lipids. Under normal conditions and in tumorigenesis, decreased levels of triglyceride (TG) and fatty acids (FAs) are observed in the mTORC2-deficient liver. However, during liver regeneration, their levels increase in the absence of mTORC2. METHODS: Rictor liver-specific knockout and control mice underwent partial hepatectomy, followed by measurement of TG and FA contents during liver regeneration. FA metabolism was evaluated by analyzing the expression of FA metabolism-related genes and proteins. Intraperitoneal injection of the peroxisome proliferator-activated receptor α (PPAR-α) agonist, p53 inhibitor, and protein kinase B (AKT) activator was performed to verify the regulatory pathways involved. Lipid mass spectrometry was performed to identify the potential PPAR-α activators. RESULTS: The expression of FA metabolism-related genes and proteins suggested that FAs are mainly transported into hepatocytes during liver regeneration. The PPAR-α pathway is down-regulated significantly in the mTORC2-deficient liver, resulting in the accumulation of TGs. The PPAR-α agonist WY-14643 rescued deficient liver regeneration and survival in mTORC2-deficient mice. Furthermore, lipidomic analysis suggested that mTORC2 deficiency substantially reduced glucosylceramide (GluCer) content. GluCer activated PPAR-α. GluCer treatment in vivo restored the regenerative ability and survival rates in the mTORC2-deficient group. CONCLUSIONS: Our data suggest that FAs are mainly transported into hepatocytes during liver regeneration, and their metabolism is facilitated by mTORC2 through the GluCer-PPAR-α pathway, thereby establishing a novel role for mTORC2 in lipid metabolism.