Recent studies suggest that mitochondria can be transferred between cells to support the survival of metabolically compromised cells. However, whether intercellular mitochondria transfer occurs in ...white adipose tissue (WAT) or regulates metabolic homeostasis in vivo remains unknown. We found that macrophages acquire mitochondria from neighboring adipocytes in vivo and that this process defines a transcriptionally distinct macrophage subpopulation. A genome-wide CRISPR-Cas9 knockout screen revealed that mitochondria uptake depends on heparan sulfates (HS). High-fat diet (HFD)-induced obese mice exhibit lower HS levels on WAT macrophages and decreased intercellular mitochondria transfer from adipocytes to macrophages. Deletion of the HS biosynthetic gene Ext1 in myeloid cells decreases mitochondria uptake by WAT macrophages, increases WAT mass, lowers energy expenditure, and exacerbates HFD-induced obesity in vivo. Collectively, this study suggests that adipocytes and macrophages employ intercellular mitochondria transfer as a mechanism of immunometabolic crosstalk that regulates metabolic homeostasis and is impaired in obesity.
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•Adipocytes transfer their mitochondria to macrophages in vivo•Mitochondria transfer from adipocytes to macrophages is decreased in obesity•Mitochondria uptake by macrophages is mediated by heparan sulfates•Mice that lack heparan sulfates on macrophages exhibit metabolic dysfunction
Brestoff et al. show that adipose-tissue-resident macrophages acquire mitochondria from neighboring adipocytes in a heparan-sulfate-dependent process that is impaired in obesity. Genetic disruption of mitochondria uptake by macrophages reduces energy expenditure and exacerbates diet-induced obesity in mice, indicating that intercellular mitochondria transfer to macrophages mediates systemic metabolic homeostasis.
Autophagy functions in antiviral immunity. However, the ability of endogenous autophagy genes to protect against viral disease in vertebrates remains to be causally established. Here, we report that ...the autophagy gene Atg5 function is critical for protection against lethal Sindbis virus (SIN) infection of the mouse central nervous system. Inactivating Atg5 in SIN-infected neurons results in delayed clearance of viral proteins, increased accumulation of the cellular p62 adaptor protein, and increased cell death in neurons, but the levels of viral replication remain unaltered. In vitro, p62 interacts with SIN capsid protein, and genetic knockdown of p62 blocks the targeting of viral capsid to autophagosomes. Moreover, p62 or autophagy gene knockdown increases viral capsid accumulation and accelerates virus-induced cell death without affecting virus replication. These results suggest a function for autophagy in mammalian antiviral defense: a cell-autonomous mechanism in which p62 adaptor-mediated autophagic viral protein clearance promotes cell survival.
The study of macroautophagy in mammalian cells has described induction, vesicle nucleation, and membrane elongation complexes as key signaling intermediates driving autophagosome biogenesis. How ...these components are recruited to nascent autophagosomes is poorly understood, and although much is known about signaling mechanisms that restrain autophagy, the nature of positive inductive signals that can promote autophagy remain cryptic. We find that the Ras-like small G protein, RalB, is localized to nascent autophagosomes and is activated on nutrient deprivation. RalB and its effector Exo84 are required for nutrient starvation-induced autophagocytosis, and RalB activation is sufficient to promote autophagosome formation. Through direct binding to Exo84, RalB induces the assembly of catalytically active ULK1 and Beclin1-VPS34 complexes on the exocyst, which are required for isolation membrane formation and maturation. Thus, RalB signaling is a primary adaptive response to nutrient limitation that directly engages autophagocytosis through mobilization of the core vesicle nucleation machinery.
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► RalB activation is a proximal signal to the promotion of autophagy ► The exocyst is a RalB effector required for nutrient deprivation-induced autophagy ► Exo84 and Sec5 are positive and negative regulatory partners for Beclin1 and ULK1 ► RalB binding induces Exo84-dependent ULK1 activation and autophagosome biogenesis
Autophagy is an evolutionarily ancient pathway for survival during different forms of cellular stress, including infection with viruses and other intracellular pathogens. Autophagy may protect ...against viral infection through degradation of viral components (xenophagy), by promoting the survival or death of infected cells, through delivery of Toll-like receptor (TLR) ligands to endosomes to activate innate immunity, or by feeding antigens to MHC class II compartments to activate adaptive immunity. Given this integral role of autophagy in innate and adaptive antiviral immunity, selective pressure likely promoted the emergence of escape mechanisms by pathogenic viruses. This review will briefly summarize the current understanding of autophagy as an antiviral pathway, and then discuss strategies that viruses may utilize to evade this host defense mechanism.
Commensal microbes profoundly impact host immunity to enteric viral infections
. We have shown that the bacterial microbiota and host antiviral cytokine interferon-λ (IFN-λ) determine the persistence ...of murine norovirus in the gut
. However, the effects of the virome in modulating enteric infections remain unexplored. Here, we report that murine astrovirus can complement primary immunodeficiency to protect against murine norovirus and rotavirus infections. Protection against infection was horizontally transferable between immunocompromised mouse strains by co-housing and fecal transplantation. Furthermore, protection against enteric pathogens corresponded with the presence of a specific strain of murine astrovirus in the gut, and this complementation of immunodeficiency required IFN-λ signalling in gut epithelial cells. Our study demonstrates that elements of the virome can protect against enteric pathogens in an immunodeficient host.
Genes required for the lysosomal degradation pathway of autophagy play key roles in topologically distinct and physiologically important cellular processes. Some functions of
genes are independent of ...their role in degradative autophagy. One of the first described of these
gene-dependent, but degradative autophagy independent, processes is the requirement for a subset of
genes in interferon-γ (IFNγ)-induced inhibition of norovirus and
replication. Herein, we identified additional genes that are required for, or that negatively regulate, this innate immune effector pathway. Enzymes in the UFMylation pathway negatively regulated IFNγ-induced inhibition of norovirus replication via effects of
. IFNγ-induced inhibition of norovirus replication required
(also termed
),
,
,
, and
but not
(encoding Beclin 1),
,
, or
. The phosphatidylinositol-3-phosphate and ATG16L1-binding domains of WIPI2B, as well as the ATG5-binding domain of ATG16L1, were required for IFNγ-induced inhibition of norovirus replication. Other members of the
,
, and
gene families were not required, demonstrating exquisite specificity within these gene families for participation in IFNγ action. The generality of some aspects of this mechanism was demonstrated by a role for GATE-16 and WIPI2 in IFNγ-induced control of
infection in human cells. These studies further delineate the genes and mechanisms of an
gene-dependent programmable form of cytokine-induced innate intracellular immunity. IMPORTANCE Interferon-γ (IFNγ) is a critical mediator of cell-intrinsic immunity to intracellular pathogens. Understanding the complex cellular mechanisms supporting robust interferon-γ-induced host defenses could aid in developing new therapeutics to treat infections. Here, we examined the impact of autophagy genes in the interferon-γ-induced host response. We demonstrate that genes within the autophagy pathway including
,
, and
, as well as ubiquitin ligase complex genes
and
are required for IFNγ-induced inhibition of murine norovirus (norovirus hereinafter) replication in mouse cells.
and
were also required for IFNγ-mediated restriction of parasite growth within the
parasitophorous vacuole in human cells. Furthermore, we found that perturbation of UFMylation pathway components led to more robust IFNγ-induced inhibition of norovirus via regulation of endoplasmic reticulum (ER) stress. Enhancing or inhibiting these dynamic cellular components could serve as a strategy to control intracellular pathogens and maintain an effective immune response.
The bacterial pathogen Vibrio parahaemolyticus utilizes a type III secretion system to cause death of host cells within hours of infection. We report that cell death is completely independent of ...apoptosis and occurs by a mechanism in which injection of multiple type III effectors causes induction of autophagy, cell rounding, and the subsequent release of cellular contents. Autophagy is detected by the appearance of lipidated light chain 3 (LC3) and by increases in punctae and vacuole formation. Electron microscopy reveals the production of early autophagic vesicles during infection. Consistent with phosphoinositide 3 (PI3) kinase playing a role in autophagy, treatment of infected cells with a PI3 kinase inhibitor attenuates autophagy in infected cells. Because many effectors are injected during a V. parahaemolyticus infection, it is not surprising that the presence of a sole PI3 kinase inhibitor does not prevent inevitable host-cell death. Our studies reveal an infection paradigm whereby an extracellular pathogen uses its type III secretion system to cause at least three parallel events that eventually result in the proinflammatory death of an infected host cell.
Lysosomal membrane permeabilization (LMP) and cathepsin release typifies lysosome-dependent cell death (LDCD). However, LMP occurs in most regulated cell death programs suggesting LDCD is not an ...independent cell death pathway, but is conscripted to facilitate the final cellular demise by other cell death routines. Previously, we demonstrated that Caenorhabditis elegans (C. elegans) null for a cysteine protease inhibitor, srp-6, undergo a specific LDCD pathway characterized by LMP and cathepsin-dependent cytoplasmic proteolysis. We designated this cell death routine, lysoptosis, to distinguish it from other pathways employing LMP. In this study, mouse and human epithelial cells lacking srp-6 homologues, mSerpinb3a and SERPINB3, respectively, demonstrated a lysoptosis phenotype distinct from other cell death pathways. Like in C. elegans, this pathway depended on LMP and released cathepsins, predominantly cathepsin L. These studies suggested that lysoptosis is an evolutionarily-conserved eukaryotic LDCD that predominates in the absence of neutralizing endogenous inhibitors.
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