bims-nocaut 2023-06-18 papers

Issue of 2023–06–18
three papers selected by
Quentin Frenger, University of Strasbourg

Clin Exp Med. 2023 Jun 13.

Reduction in Rubicon by cigarette smoke is associated with impaired phagocytosis and occurs through lysosomal degradation pathway.

Patrick F Asare, Plinio R Hurtado, Hai B Tran, Griffith B Perkins, Eugene Roscioli, Sandra Hodge.

BACKGROUND: A common feature of COPD is a defective lung macrophage phagocytic capacity that can contribute to chronic lung inflammation and infection. The precise mechanisms remain incompletely understood, although cigarette smoke is a known contributor. We previously showed deficiency of the LC3-associated phagocytosis (LAP) regulator, Rubicon, in macrophages from COPD subjects and in response to cigarette smoke. The current study investigated the molecular basis by which cigarette smoke extract (CSE) reduces Rubicon in THP-1, alveolar and blood monocyte-derived macrophages, and the relationship between Rubicon deficiency and CSE-impaired phagocytosis.
METHODOLOGY: Phagocytic capacity of CSE-treated macrophages was measured by flow cytometry, Rubicon expression by Western blot and real time polymerase chain reaction, and autophagic-flux by LC3 and p62 levels. The effect of CSE on Rubicon degradation was determined using cycloheximide inhibition and Rubicon protein synthesis and half-life assessment.
RESULTS: Phagocytosis was significantly impaired in CSE-exposed macrophages and strongly correlated with Rubicon expression. CSE-impaired autophagy, accelerated Rubicon degradation, and reduced its half-life. Lysosomal protease inhibitors, but not proteasome inhibitors, attenuated this effect. Autophagy induction did not significantly affect Rubicon expression.
CONCLUSIONS: CSE decreases Rubicon through the lysosomal degradation pathway. Rubicon degradation and/or LAP impairment may contribute to dysregulated phagocytosis perpetuated by CSE.

Keywords: Autophagy; Inflammation; LC3-associated phagocytosis (LAP); Phagocytosis; Rubicon

DOI: https://doi.org/10.1007/s10238-023-01105-1

Dev Cell. 2023 Jun 08. pii: S1534-5807(23)00242-3. [Epub ahead of print]

LC3B is lipidated to large lipid droplets during prolonged starvation for noncanonical autophagy.

Mohyeddine Omrane, Kalthoum Ben M'Barek, Alexandre Santinho, Nathan Nguyen, Shanta Nag, Thomas J Melia, Abdou Rachid Thiam.

Lipid droplets (LDs) store lipids that can be utilized during times of scarcity via autophagic and lysosomal pathways, but how LDs and autophagosomes interact remained unclear. Here, we discovered that the E2 autophagic enzyme, ATG3, localizes to the surface of certain ultra-large LDs in differentiated murine 3T3-L1 adipocytes or Huh7 human liver cells undergoing prolonged starvation. Subsequently, ATG3 lipidates microtubule-associated protein 1 light-chain 3B (LC3B) to these LDs. In vitro, ATG3 could bind alone to purified and artificial LDs to mediate this lipidation reaction. We observed that LC3B-lipidated LDs were consistently in close proximity to collections of LC3B-membranes and were lacking Plin1. This phenotype is distinct from macrolipophagy, but it required autophagy because it disappeared following ATG5 or Beclin1 knockout. Our data suggest that extended starvation triggers a noncanonical autophagy mechanism, similar to LC3B-associated phagocytosis, in which the surface of large LDs serves as an LC3B lipidation platform for autophagic processes.

Keywords: Atg3; LC3B; lipid droplets; noncanonical autophagy; organelle biogenesis; prolonged starvation

DOI: https://doi.org/10.1016/j.devcel.2023.05.009

PLoS Biol. 2023 Jun 15. 21(6): e3002159

Autophagy prevents early proinflammatory responses and neutrophil recruitment during Mycobacterium tuberculosis infection without affecting pathogen burden in macrophages.

Rachel L Kinsella, Jacqueline M Kimmey, Asya Smirnov, Reilly Woodson, Margaret R Gaggioli, Sthefany M Chavez, Darren Kreamalmeyer, Christina L Stallings.

The immune response to Mycobacterium tuberculosis infection determines tuberculosis disease outcomes, yet we have an incomplete understanding of what immune factors contribute to a protective immune response. Neutrophilic inflammation has been associated with poor disease prognosis in humans and in animal models during M. tuberculosis infection and, therefore, must be tightly regulated. ATG5 is an essential autophagy protein that is required in innate immune cells to control neutrophil-dominated inflammation and promote survival during M. tuberculosis infection; however, the mechanistic basis for how ATG5 regulates neutrophil recruitment is unknown. To interrogate what innate immune cells require ATG5 to control neutrophil recruitment during M. tuberculosis infection, we used different mouse strains that conditionally delete Atg5 in specific cell types. We found that ATG5 is required in CD11c+ cells (lung macrophages and dendritic cells) to control the production of proinflammatory cytokines and chemokines during M. tuberculosis infection, which would otherwise promote neutrophil recruitment. This role for ATG5 is autophagy dependent, but independent of mitophagy, LC3-associated phagocytosis, and inflammasome activation, which are the most well-characterized ways that autophagy proteins regulate inflammation. In addition to the increased proinflammatory cytokine production from macrophages during M. tuberculosis infection, loss of ATG5 in innate immune cells also results in an early induction of TH17 responses. Despite prior published in vitro cell culture experiments supporting a role for autophagy in controlling M. tuberculosis replication in macrophages, the effects of autophagy on inflammatory responses occur without changes in M. tuberculosis burden in macrophages. These findings reveal new roles for autophagy proteins in lung resident macrophages and dendritic cells that are required to suppress inflammatory responses that are associated with poor control of M. tuberculosis infection.

DOI: https://doi.org/10.1371/journal.pbio.3002159