Mitochondrial autophagy, or mitophagy, is a major mechanism involved in mitochondrial quality control via selectively removing damaged or unwanted mitochondria. Interactions between LC3 and mitophagy receptors such as FUNDC1, which harbors an LC3-interacting region (LIR), are essential for this selective process. However, how mitochondrial stresses are sensed to activate receptor-mediated mitophagy remains poorly defined. Here, we identify that the mitochondrially localized PGAM5 phosphatase interacts with and dephosphorylates FUNDC1 at serine 13 (Ser-13) upon hypoxia or carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) treatment. Dephosphorylation of FUNDC1 catalyzed by PGAM5 enhances its interaction with LC3, which is abrogated following knockdown of PGAM5 or the introduction of a cell-permeable unphosphorylated peptide encompassing the Ser-13 and LIR of FUNDC1. We further observed that CK2 phosphorylates FUNDC1 to reverse the effect of PGAM5 in mitophagy activation. Our results reveal a mechanistic signaling pathway linking mitochondria-damaging signals to the dephosphorylation of FUNDC1 by PGAM5, which ultimately induces mitophagy.
Aging is an important factor in memory decline in aged animals and humans and in Alzheimer's disease and is associated with the impairment of hippocampal long-term potentiation (LTP) and downregulation of NR1/NR2B expression. Gaseous formaldehyde exposure is known to induce animal memory loss and human cognitive decline; however, it is unclear whether the concentrations of endogenous formaldehyde are elevated in the hippocampus and how excess formaldehyde affects LTP and memory formation during the aging process. In the present study, we report that hippocampal formaldehyde accumulated in memorydeteriorating diseases such as age-related dementia. Spatial memory performance was gradually impaired in normal Sprague-Dawley rats by persistent intraperitoneal injection with formaldehyde. Furthermore, excess formaldehyde treatment suppressed the hippocampal LTP formation by blocking N-methyl-D-aspartate (NMDA) receptor. Chronic excess formaldehyde treatment over a period of 30 days markedly decreased the viability of the hippocampus and down-regulated the expression of the NR1 and NR2B subunits of the NMDA receptor. Our results indicate that excess endogenous formaldehyde is a critical factor in memory loss in age-related memory-deteriorating diseases.
MicroRNA-146a protects the myocardium from I/R injury. The mechanisms may involve attenuation of NF-κB activation and inflammatory cytokine production by suppressing IRAK1 and TRAF6.
Recent evidence from cancer research indicates that lactate exerts a suppressive effect on innate immune responses in cancer. This study investigated the mechanisms by which lactate suppresses macrophage pro-inflammatory responses. Macrophages [Raw 264.7 and bone marrow derived macrophages (BMDMs)] were treated with LPS in the presence or absence of lactate. Pro-inflammatory cytokines, NF-κB and YAP activation and nuclear translocation were examined. Our results show that lactate significantly attenuates LPS stimulated macrophage TNF-α and IL-6 production. Lactate also suppresses LPS stimulated macrophage NF-κB and YAP activation and nuclear translocation in macrophages. Interestingly, YAP activation and nuclear translocation are required for LPS stimulated macrophage NF-κB activation and TNFα production. Importantly, lactate suppressed YAP activation and nuclear translocation is mediated by GPR81 dependent AMKP and LATS activation which phosphorylates YAP, resulting in YAP inactivation. Finally, we demonstrated that LPS stimulation induces an interaction between YAP and NF-κB subunit p65, while lactate decreases the interaction of YAP and NF-κB, thus suppressing LPS induced pro-inflammatory cytokine production. Our study demonstrates that lactate exerts a previously unknown role in the suppression of macrophage pro-inflammatory cytokine production via GPR81 mediated YAP inactivation, resulting in disruption of YAP and NF-κB interaction and nuclear translocation in macrophages.
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