Biology subjects

Berk, B. C.

Publications and source records attributed to Berk, B. C..

3 recordsLinked to original sources

bioRxiv2022

Pnpt1 mediates NLRP3 inflammasome activation by MAVS and metabolic reprogramming in macrophages

Polyribonucleotide nucleotidyltransferase 1 (Pnpt1) plays critical roles in mitochondrial homeostasis by controlling mitochondrial RNA (mt-RNA) processing, trafficking and degradation. Pnpt1 deficiency results in mitochondrial dysfunction that triggers a Type I interferon response, suggesting a role in inflammation. However, the role of Pnpt1 in inflammasome activation remains largely unknown. In this study, we generated myeloid-specific Pnpt1-knockout mice, and demonstrated that Pnpt1 depletion enhanced interleukin-1 beta (IL-1{beta}) and interleukin-18 (IL-18) secretion in mouse sepsis models. Using cultured peritoneal and bone marrow-derived macrophages we demonstrated that Pnpt1 regulated NLRP3 inflammasome dependent IL-1{beta} release in response to lipopolysaccharides (LPS), followed by nigericin, ATP or poly (I:C) treatment. Pnpt1 deficiency in macrophages increased glycolysis after LPS, and mt-reactive oxygen species (mt-ROS) after NLRP3 inflammasome activation. Pnpt1 activation of the inflammasome was dependent on both increased glycolysis and expression of the mitochondrial antiviral-signaling protein (MAVS), but not NF-{kappa}B signaling. Collectively, these data strengthen the concept that Pnpt1 is an important mediator of inflammation as shown by activation of the NLRP3 inflammasome in mouse sepsis and cultured macrophages.

immunology↗

bioRxiv2022

The lipid peroxidation product 4-hydroxynonenal inhibits NLRP3 inflammasome activation and macrophage pyroptosis

Pyroptosis is a form of cell death triggered by the innate immune system that has been implicated in the pathogenesis of sepsis and acute lung injury. At the cellular level, pyroptosis is characterized by cell swelling, membrane rupture, and release of inflammatory cytokines, such as IL-1{beta}. However, the role of endogenous lipids in pyroptosis remains underappreciated. We discovered that 4-hydroxynonenal (HNE), a major endogenous product of lipid peroxidation, inhibited pyroptosis and inflammasome activation. HNE at physiological concentrations (3 {micro}M) blocked nigericin and ATP-induced cell death, as well as secretion of IL-1{beta}, by mouse primary macrophages and human peripheral blood mononuclear cells. Treatment with HNE, or an increase of endogenous HNE by inhibiting glutathione peroxidase 4, reduced inflammasome activation in mouse models of acute lung injury and sepsis. Mechanistically, HNE inhibited the NLRP3 inflammasome activation independently of Nrf2 and NF-{kappa}B signaling, and had no effect on the AIM2 inflammasome. Furthermore, HNE directly bound to NLRP3 and inhibited its interaction with NEK7. Our findings identify HNE as a novel, endogenous inhibitor of the NLRP3 inflammasome.

immunology↗

bioRxiv2021

Cyclophilin A regulates protein phase separation and mitigates haematopoietic stem cell aging

Loss of protein quality is a driving force of aging1. The accumulation of misfolded proteins represents a vulnerability for long-lived cells, such as haematopoietic stem cells. How these cells, which have the ability to reconstitute all haematopoietic lineages throughout life2, maintain their regenerative potential and avert the effects of aging is poorly understood. Here, we determined the protein content in haematopoietic stem and progenitor cells to identify prevalent chaperones that support proteome integrity. We identified Peptidyl-Prolyl Isomerase A (PPIA or Cyclophilin A) as the dominant cytosolic foldase in this cell population. Loss of PPIA accelerated aging in the mouse stem cell compartment. In an effort to define targets of PPIA, we found that RNA- and DNA-binding proteins are common substrates of this chaperone. These proteins are enriched in intrinsically disordered regions (IDRs), which can catalyse protein condensation3. Isomerized target prolines are almost exclusively located within IDRs. We discovered that over 20% of PPIA client proteins are known to participate in liquid-liquid phase separation, enabling the formation of supramolecular membrane-less organelles. Using the poly-A binding protein PABPC1 as an example, we demonstrate that PPIA promotes phase separation of ribonucleoprotein particles, thereby increasing cellular stress resistance. Haematopoietic stem cell aging is associated with a decreased expression of PPIA and reduced synthesis of intrinsically disordered proteins. Our findings link the ubiquitously expressed chaperone PPIA to phase transition and identify macromolecular condensation as a potential determinant of the aging process in haematopoietic stem cells.

cell biology↗