Rapamycin mitigates inflammation-mediated disc matrix homeostatic imbalance by inhibiting mTORC1 and inducing autophagy through Akt activation.

Background: Low back pain is a global health problem that originated mainly from intervertebral disc degeneration (IDD). Autophagy, negatively regulated by the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway, prevents metabolic and degenerative diseases by removing and recycling damaged cellular components. Despite growing evidence that autophagy occurs in the intervertebral disc, the regulation of disc cellular autophagy is still poorly understood. Methods: Annulus fibrosus (rAF) cell cultures derived from healthy female rabbit discs were used to test the effect of autophagy inhibition or activation on disc cell fate and matrix homeostasis. Specifically, different chemical inhibitors including rapamycin, 3-methyladenine, MK-2206, and PP242 were used to modulate activities of different proteins in the PI3K/Akt/mTOR signaling pathway to assess IL-1ß-induced cellular senescence, apoptosis, and matrix homeostasis in rAF cells grown under nutrient-poor culture condition. Results: Rapamycin, an inhibitor of mTOR complex 1 (mTORC1), reduced the phosphorylation of mTOR and its effector p70/S6K in rAF cell cultures. Rapamycin also induced autophagic flux as measured by increased expression of key autophagy markers, including LC3 puncta number, LC3-II expression, and cytoplasmic HMGB1 intensity and decreased p62/SQSTM1 expression. As expected, IL-1ß stimulation promoted rAF cellular senescence, apoptosis, and matrix homeostatic imbalance with enhanced aggrecanolysis and MMP-3 and MMP-13 expression. Rapamycin treatment effectively mitigated IL-1ß-mediated inflammatory stress changes, but these alleviating effects of rapamycin were abrogated by chemical inhibition of Akt and mTOR complex 2 (mTORC2). Conclusions: These findings suggest that rapamycin blunts adverse effects of inflammation on disc cells by inhibiting mTORC1 to induce autophagy through the PI3K/Akt/mTOR pathway that is dependent on Akt and mTORC2 activities. Hence, our findings identify autophagy, rapamycin, and PI3K/Akt/mTOR signaling as potential therapeutic targets for IDD treatment.

Impact of autophagy inhibition on intervertebral disc cells and extracellular matrix.

Background: Intervertebral disc degeneration (IDD) is a leading contributor to low back pain (LBP). Autophagy, strongly activated by hypoxia and nutrient starvation, is a vital intracellular quality control process that removes damaged proteins and organelles to recycle them for cellular biosynthesis and energy production. While well-established as a major driver of many age-related diseases, autophagy dysregulation or deficiency has yet been confirmed to cause IDD. Methods: In vitro, rat nucleus pulposus (NP) cells treated with bafilomycin A1 to inhibit autophagy were assessed for glycosaminoglycan (GAG) content, proteoglycan synthesis, and cell viability. In vivo, a transgenic strain (Col2a1-Cre; Atg7 fl/fl) mice were successfully generated to inhibit autophagy primarily in NP tissues. Col2a1-Cre; Atg7 fl/fl mouse intervertebral discs (IVDs) were evaluated for biomarkers for apoptosis and cellular senescence, aggrecan content, and histological changes up to 12 months of age. Results: Here, we demonstrated inhibition of autophagy by bafilomycin produced IDD features in the rat NP cells, including increased apoptosis and cellular senescence (p21 CIP1) and decreased expression of disc matrix genes Col2a1 and Acan. H&E histologic staining showed significant but modest degenerative changes in NP tissue of Col2a1-Cre; Atg7 fl/fl mice compared to controls at 6 and 12 months of age. Intriguingly, 12-month-old Col2a1-Cre; Atg7 fl/fl mice did not display increased loss of NP proteoglycan. Moreover, markers of apoptosis (cleaved caspase-3, TUNEL), and cellular senescence (p53, p16 INK4a , IL-1ß, TNF-α) were not affected in 12-month-old Col2a1-Cre; Atg7 fl/fl mice compared to controls. However, p21 CIP1and Mmp13 gene expression were upregulated in NP tissue of 12-month-old Col2a1-Cre; Atg7 fl/fl mice compared to controls, suggesting p21 CIP1-mediated cellular senescence resulted from NP-targeted Atg7 knockout might contribute to the observed histological changes. Conclusion: The absence of overt IDD features from disrupting Atg7-mediated macroautophagy in NP tissue implicates other compensatory mechanisms, highlighting additional research needed to elucidate the complex biology of autophagy in regulating age-dependent IDD.

Cellular Senescence in Intervertebral Disc Aging and Degeneration: Molecular Mechanisms and Potential Therapeutic Opportunities.

Closely associated with aging and age-related disorders, cellular senescence (CS) is the inability of cells to proliferate due to accumulated unrepaired cellular damage and irreversible cell cycle arrest. Senescent cells are characterized by their senescence-associated secretory phenotype that overproduces inflammatory and catabolic factors that hamper normal tissue homeostasis. Chronic accumulation of senescent cells is thought to be associated with intervertebral disc degeneration (IDD) in an aging population. This IDD is one of the largest age-dependent chronic disorders, often associated with neurological dysfunctions such as, low back pain, radiculopathy, and myelopathy. Senescent cells (SnCs) increase in number in the aged, degenerated discs, and have a causative role in driving age-related IDD. This review summarizes current evidence supporting the role of CS on onset and progression of age-related IDD. The discussion includes molecular pathways involved in CS such as p53-p21CIP1, p16INK4a, NF-κB, and MAPK, and the potential therapeutic value of targeting these pathways. We propose several mechanisms of CS in IDD including mechanical stress, oxidative stress, genotoxic stress, nutritional deprivation, and inflammatory stress. There are still large knowledge gaps in disc CS research, an understanding of which will provide opportunities to develop therapeutic interventions to treat age-related IDD.

Dimethyl itaconate is effective in host-directed antimicrobial responses against mycobacterial infections through multifaceted innate immune pathways.

BACKGROUND: Itaconate, a crucial immunometabolite, plays a critical role in linking immune and metabolic functions to influence host defense and inflammation. Due to its polar structure, the esterified cell-permeable derivatives of itaconate are being developed to provide therapeutic opportunities in infectious and inflammatory diseases. Yet, it remains largely uncharacterized whether itaconate derivatives have potentials in promoting host-directed therapeutics (HDT) against mycobacterial infections. Here, we report dimethyl itaconate (DMI) as the promising candidate for HDT against both Mycobacterium tuberculosis (Mtb) and nontuberculous mycobacteria by orchestrating multiple innate immune programs. RESULTS: DMI per se has low bactericidal activity against Mtb, M. bovis Bacillus Calmette-Guérin (BCG), and M. avium (Mav). However, DMI robustly activated intracellular elimination of multiple mycobacterial strains (Mtb, BCG, Mav, and even to multidrug-resistant Mtb) in macrophages and in vivo. DMI significantly suppressed the production of interleukin-6 and -10, whereas it enhanced autophagy and phagosomal maturation, during Mtb infection. DMI-mediated autophagy partly contributed to antimicrobial host defenses in macrophages. Moreover, DMI significantly downregulated the activation of signal transducer and activator of transcription 3 signaling during infection with Mtb, BCG, and Mav. CONCLUSION: Together, DMI has potent anti-mycobacterial activities in macrophages and in vivo through promoting multifaceted ways for innate host defenses. DMI may bring light to new candidate for HDT against Mtb and nontuberculous mycobacteria, both of which infections are often intractable with antibiotic resistance.

Peroxisome Proliferator-Activated Receptor-Targeted Therapies: Challenges upon Infectious Diseases.

Peroxisome proliferator-activated receptors (PPARs) α, ß, and γ are nuclear receptors that orchestrate the transcriptional regulation of genes involved in a variety of biological responses, such as energy metabolism and homeostasis, regulation of inflammation, cellular development, and differentiation. The many roles played by the PPAR signaling pathways indicate that PPARs may be useful targets for various human diseases, including metabolic and inflammatory conditions and tumors. Accumulating evidence suggests that each PPAR plays prominent but different roles in viral, bacterial, and parasitic infectious disease development. In this review, we discuss recent PPAR research works that are focused on how PPARs control various infections and immune responses. In addition, we describe the current and potential therapeutic uses of PPAR agonists/antagonists in the context of infectious diseases. A more comprehensive understanding of the roles played by PPARs in terms of host-pathogen interactions will yield potential adjunctive personalized therapies employing PPAR-modulating agents.

Chemical mimetics of the N-degron pathway alleviate systemic inflammation by activating mitophagy and immunometabolic remodeling.

The Arg/N-degron pathway, which is involved in the degradation of proteins bearing an N-terminal signal peptide, is connected to p62/SQSTM1-mediated autophagy. However, the impact of the molecular link between the N-degron and autophagy pathways is largely unknown in the context of systemic inflammation. Here, we show that chemical mimetics of the N-degron Nt-Arg pathway (p62 ligands) decreased mortality in sepsis and inhibited pathological inflammation by activating mitophagy and immunometabolic remodeling. The p62 ligands alleviated systemic inflammation in a mouse model of lipopolysaccharide (LPS)-induced septic shock and in the cecal ligation and puncture model of sepsis. In macrophages, the p62 ligand attenuated the production of proinflammatory cytokines and chemokines in response to various innate immune stimuli. Mechanistically, the p62 ligand augmented LPS-induced mitophagy and inhibited the production of mitochondrial reactive oxygen species in macrophages. The p62 ligand-mediated anti-inflammatory, antioxidative, and mitophagy-activating effects depended on p62. In parallel, the p62 ligand significantly downregulated the LPS-induced upregulation of aerobic glycolysis and lactate production. Together, our findings demonstrate that p62 ligands play a critical role in the regulation of inflammatory responses by orchestrating mitophagy and immunometabolic remodeling.

Dysregulated thrombospondin 1 and miRNA-29a-3p in severe COVID-19.

Although nearly a fifth of symptomatic COVID-19 patients suffers from severe pulmonary inflammation, the mechanism of developing severe illness is not yet fully understood. To identify significantly altered genes in severe COVID-19, we generated messenger RNA and micro-RNA profiling data of peripheral blood mononuclear cells (PBMCs) from five COVID-19 patients (2 severe and 3 mild patients) and three healthy controls (HC). For further evaluation, two publicly available RNA-Seq datasets (GSE157103 and GSE152418) and one single-cell RNA-Seq dataset (GSE174072) were employed. Based on RNA-Seq datasets, thrombospondin 1 (THBS1) and interleukin-17 receptor A (IL17RA) were significantly upregulated in severe COVID-19 patients' blood. From single-cell RNA-sequencing data, IL17RA level is increased in monocytes and neutrophils, whereas THBS1 level is mainly increased in the platelets. Moreover, we identified three differentially expressed microRNAs in severe COVID-19 using micro-RNA sequencings. Intriguingly, hsa-miR-29a-3p significantly downregulated in severe COVID-19 was predicted to bind the 3'-untranslated regions of both IL17RA and THBS1 mRNAs. Further validation analysis of our cohort (8 HC, 7 severe and 8 mild patients) showed that THBS1, but not IL17RA, was significantly upregulated, whereas hsa-miR-29a-3p was downregulated, in PBMCs from severe patients. These findings strongly suggest that dysregulated expression of THBS1, IL17RA, and hsa-miR-29a-3p involves severe COVID-19.

Ohmyungsamycin promotes M1-like inflammatory responses to enhance host defence against Mycobacteroides abscessus infections.

Ohmyungsamycin A (OMS) is a newly identified cyclic peptide that exerts antimicrobial effects against Mycobacterium tuberculosis. However, its role in nontuberculous mycobacteria (NTMs) infections has not been clarified. Mycobacteroides abscessus (Mabc) is a rapidly growing NTM that has emerged as a human pathogen in both immunocompetent and immunosuppressed individuals. In this study, we demonstrated that OMS had significant antimicrobial effects against Mabc infection in both immunocompetent and immunodeficient mice, and in macrophages. OMS treatment amplified Mabc-induced expression of M1-related proinflammatory cytokines and inducible nitric oxide synthase, and significantly downregulated arginase-1 expression in murine macrophages. In addition, OMS augmented Mabc-mediated production of mitochondrial reactive oxygen species (mtROS), which promoted M1-like proinflammatory responses in Mabc-infected macrophages. OMS-induced production of mtROS and nitric oxide was critical for OMS-mediated antimicrobial responses during Mabc infections. Notably, the combination of OMS and rifabutin had a synergistic effect on the antimicrobial responses against Mabc infections in vitro, in murine macrophages, and in zebrafish models in vivo. Collectively, these data strongly suggest that OMS may be an effective M1-like adjunctive therapeutic against Mabc infections, either alone or in combination with antibiotics.

Targeting ERRα promotes cytotoxic effects against acute myeloid leukemia through suppressing mitochondrial oxidative phosphorylation.

Acute myeloid leukemia (AML) is an aggressive blood cancer with poor clinical outcomes. Emerging data suggest that mitochondrial oxidative phosphorylation (mtOXPHOS) plays a significant role in AML tumorigenesis, progression, and resistance to chemotherapies. However, how the mtOXPHOS is regulated in AML cells is not well understood. In this study, we investigated the oncogenic functions of ERRα in AML by combining in silico, in vitro, and in vivo analyses and showed ERRα is a key regulator of mtOXPHOS in AML cells. The increased ERRα level was associated with worse clinical outcomes of AML patients. Single cell RNA-Seq analysis of human primary AML cells indicated that ERRα-expressing cancer cells had significantly higher mtOXPHOS enrichment scores. Blockade of ERRα by pharmacologic inhibitor (XCT-790) or gene silencing suppressed mtOXPHOS and increased anti-leukemic effects in vitro and in xenograft mouse models.

Sirtuin 1 in Host Defense during Infection.

Sirtuins (SIRTs) are members of the class III histone deacetylase family and epigenetically control multiple target genes to modulate diverse biological responses in cells. Among the SIRTs, SIRT1 is the most well-studied, with a role in the modulation of immune and inflammatory responses following infection. The functions of SIRT1 include orchestrating immune, inflammatory, metabolic, and autophagic responses, all of which are required in establishing and controlling host defenses during infection. In this review, we summarize recent information on the roles of SIRT1 and its regulatory mechanisms during bacterial, viral, and parasitic infections. We also discuss several SIRT1 modulators, as potential antimicrobial treatments. Understanding the function of SIRT1 in balancing immune homeostasis will contribute to the development of new therapeutics for the treatment of infection and inflammatory disease.

The dual role of autophagy in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a severe hematologic malignancy prevalent in older patients, and the identification of potential therapeutic targets for AML is problematic. Autophagy is a lysosome-dependent catabolic pathway involved in the tumorigenesis and/or treatment of various cancers. Mounting evidence has suggested that autophagy plays a critical role in the initiation and progression of AML and anticancer responses. In this review, we describe recent updates on the multifaceted functions of autophagy linking to genetic alterations of AML. We also summarize the latest evidence for autophagy-related genes as potential prognostic predictors and drivers of AML tumorigenesis. We then discuss the crosstalk between autophagy and tumor cell metabolism into the impact on both AML progression and anti-leukemic treatment. Moreover, a series of autophagy regulators, i.e., the inhibitors and activators, are described as potential therapeutics for AML. Finally, we describe the translation of autophagy-modulating therapeutics into clinical practice. Autophagy in AML is a double-edged sword, necessitating a deeper understanding of how autophagy influences dual functions in AML tumorigenesis and anti-leukemic responses.

Arginine-mediated gut microbiome remodeling promotes host pulmonary immune defense against nontuberculous mycobacterial infection.

Nontuberculous mycobacterial pulmonary diseases (NTM-PDs) are emerging as global health threats with issues of antibiotic resistance. Accumulating evidence suggests that the gut-lung axis may provide novel candidates for host-directed therapeutics against various infectious diseases. However, little is known about the gut-lung axis in the context of host protective immunity to identify new therapeutics for NTM-PDs. This study was performed to identify gut microbes and metabolites capable of conferring pulmonary immunity to NTM-PDs. Using metabolomics analysis of sera from NTM-PD patients and mouse models, we showed that the levels of l-arginine were decreased in sera from NTM-PD patients and NTM-infected mice. Oral administration of l-arginine significantly enhanced pulmonary antimicrobial activities with the expansion of IFN-γ-producing effector T cells and a shift to microbicidal (M1) macrophages in the lungs of NTM-PD model mice. Mice that received fecal microbiota transplants from l-arginine-treated mice showed increased protective host defense in the lungs against NTM-PD, whereas l-arginine-induced pulmonary host defense was attenuated in mice treated with antibiotics. Using 16S rRNA sequencing, we further showed that l-arginine administration resulted in enrichment of the gut microbiota composition with Bifidobacterium species. Notably, oral treatment with either Bifidobacterium pseudolongum or inosine enhanced antimicrobial pulmonary immune defense against NTM infection, even with multidrug-resistant clinical NTM strains. Our findings indicate that l-arginine-induced gut microbiota remodeling with enrichment of B. pseudolongum boosts pulmonary immune defense against NTM infection by driving the protective gut-lung axis in vivo.

Autophagy and Host Defense in Nontuberculous Mycobacterial Infection.

Autophagy is critically involved in host defense pathways through targeting and elimination of numerous pathogens via autophagic machinery. Nontuberculous mycobacteria (NTMs) are ubiquitous microbes, have become increasingly prevalent, and are emerging as clinically important strains due to drug-resistant issues. Compared to Mycobacterium tuberculosis (Mtb), the causal pathogen for human tuberculosis, the roles of autophagy remain largely uncharacterized in the context of a variety of NTM infections. Compelling evidence suggests that host autophagy activation plays an essential role in the enhancement of antimicrobial immune responses and controlling pathological inflammation against various NTM infections. As similar to Mtb, it is believed that NTM bacteria evolve multiple strategies to manipulate and hijack host autophagy pathways. Despite this, we are just beginning to understand the molecular mechanisms underlying the crosstalk between pathogen and the host autophagy system in a battle with NTM bacteria. In this review, we will explore the function of autophagy, which is involved in shaping host-pathogen interaction and disease outcomes during NTM infections. These efforts will lead to the development of autophagy-based host-directed therapeutics against NTM infection.

Mitofusin 2, a key coordinator between mitochondrial dynamics and innate immunity.

Remodeling of mitochondrial dynamics and mitochondrial morphology plays a pivotal role in the maintenance of mitochondrial homeostasis in response to pathogenic attacks or stress stimuli. In addition to their role in metabolism and energy production, mitochondria participate in diverse biological functions, including innate immune responses driven by macrophages in response to infections or inflammatory stimuli. Mitofusin-2 (MFN2), a mitochondria-shaping protein regulating mitochondrial fusion and fission, plays a crucial role in linking mitochondrial function and innate immune responses. In this article, we review the role of MFN2 in the regulation of innate immune responses during viral and bacterial infections. We also summarize the current knowledge on the role of MFN2 in coordinating inflammatory, atherogenic, and fibrotic responses. MFN2-mediated crosstalk between mitochondrial dynamics and innate immune responses may determine the outcomes of pathogenic infections.

Mitofusin-2 boosts innate immunity through the maintenance of aerobic glycolysis and activation of xenophagy in mice.

Mitochondrial function and innate immunity are intimately linked; however, the mechanisms how mitochondrion-shaping proteins regulate innate host defense remains largely unknown. Herein we show that mitofusin-2 (MFN2), a mitochondrial fusion protein, promotes innate host defense through the maintenance of aerobic glycolysis and xenophagy via hypoxia-inducible factor (HIF)-1α during intracellular bacterial infection. Myeloid-specific MFN2 deficiency in mice impaired the antimicrobial and inflammatory responses against mycobacterial and listerial infection. Mechanistically, MFN2 was required for the enhancement of inflammatory signaling through optimal induction of aerobic glycolysis via HIF-1α, which is activated by mitochondrial respiratory chain complex I and reactive oxygen species, in macrophages. MFN2 did not impact mitophagy during infection; however, it promoted xenophagy activation through HIF-1α. In addition, MFN2 interacted with the late endosomal protein Rab7, to facilitate xenophagy during mycobacterial infection. Our findings reveal the mechanistic regulations by which MFN2 tailors the innate host defense through coordinated control of immunometabolism and xenophagy via HIF-1α during bacterial infection.

An update on the regulatory mechanisms of NLRP3 inflammasome activation.

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a multiprotein complex involved in the release of mature interleukin-1ß and triggering of pyroptosis, which is of paramount importance in a variety of physiological and pathological conditions. Over the past decade, considerable advances have been made in elucidating the molecular mechanisms underlying the priming/licensing (Signal 1) and assembly (Signal 2) involved in NLRP3 inflammasome activation. Recently, a number of studies have indicated that the priming/licensing step is regulated by complicated mechanisms at both the transcriptional and posttranslational levels. In this review, we discuss the current understanding of the mechanistic details of NLRP3 inflammasome activation with a particular emphasis on protein-protein interactions, posttranslational modifications, and spatiotemporal regulation of the NLRP3 inflammasome machinery. We also present a detailed summary of multiple positive and/or negative regulatory pathways providing upstream signals that culminate in NLRP3 inflammasome complex assembly. A better understanding of the molecular mechanisms underlying NLRP3 inflammasome activation will provide opportunities for the development of methods for the prevention and treatment of NLRP3 inflammasome-related diseases.

Regulatory Mechanisms of Autophagy-Targeted Antimicrobial Therapeutics Against Mycobacterial Infection.

Mycobacterium tuberculosis (Mtb) is an intracellular pathogen causing human tuberculosis, an infectious disease that still remains as a global health problem. Autophagy, a lysosomal degradative process, has emerged as a critical pathway to restrict intracellular Mtb growth through enhancement of phagosomal maturation. Indeed, several autophagy-modulating agents show promise as host-directed therapeutics for Mtb infection. In this Review, we discuss recent progress in our understanding the molecular mechanisms underlying the action of autophagy-modulating agents to overcome the immune escape strategies mediated by Mtb. The factors and pathways that govern such mechanisms include adenosine 5'-monophosphate-activated protein kinase, Akt/mammalian TOR kinase, Wnt signaling, transcription factor EB, cathelicidins, inflammation, endoplasmic reticulum stress, and autophagy-related genes. A further understanding of these mechanisms will facilitate the development of host-directed therapies against tuberculosis as well as infections with other intracellular bacteria targeted by autophagic degradation.

MiR-144-3p is associated with pathological inflammation in patients infected with Mycobacteroides abscessus.

Infection with rapidly growing nontuberculous mycobacteria is emerging as a global health issue; however, key host factors remain elusive. Here, we investigated the characteristic immune profiles of peripheral blood mononuclear cells (PBMCs) from patients infected with Mycobacteroides abscessus subsp. abscessus (Mabc) and M. abscessus subsp. massiliense (Mmass). Using an integrated analysis of global mRNA and microRNA expression profiles, we found that several inflammatory cytokines/chemokines [interleukin (IL)-1ß, IL-6, C-X-C motif chemokine ligand 2, and C-C motif chemokine ligand 2] and miR-144-3p were significantly upregulated in PBMCs from patients compared with those from healthy controls (HCs). Notably, there was a strong correlation between the expression levels of miR-144-3p and proinflammatory cytokines/chemokines. Similarly, upregulated expression of miR-144-3p and proinflammatory cytokines/chemokines was found in macrophages and lungs from mice after infection with Mabc and Mmass. We showed that the expression of negative regulators of inflammation (SARM1 and TNIP3) was significantly downregulated in PBMCs from the patients, although they were not putative targets of miR-144-3p. Furthermore, overexpression of miR-144-3p led to a marked increase in proinflammatory cytokines/chemokines and promoted bacterial growth in macrophages. Together, our results highlight the importance of miR-144-3p linking to pathological inflammation during M. abscessus infection.

Host-Pathogen Interactions Operative during Mycobacteroides abscessus Infection.

Mycobacteroides abscessus (previously Mycobacterium abscessus; Mabc), one of rapidly growing nontuberculous mycobacteria (NTM), is an important pathogen of NTM pulmonary diseases (NTM-PDs) in both immunocompetent and immunocompromised individuals. Mabc infection is chronic and often challenging to treat due to drug resistance, motivating the development of new therapeutics. Despite this, there is a lack of understanding of the relationship between Mabc and the immune system. This review highlights recent progress in the molecular architecture of Mabc and host interactions. We discuss several microbial components that take advantage of host immune defenses, host defense pathways that can overcome Mabc pathogenesis, and how host-pathogen interactions determine the outcomes of Mabc infection. Understanding the molecular mechanisms underlying host-pathogen interactions during Mabc infection will enable the identification of biomarkers and/or drugs to control immune pathogenesis and protect against NTM infection.

ESRRA (estrogen related receptor alpha) is a critical regulator of intestinal homeostasis through activation of autophagic flux via gut microbiota.

The orphan nuclear receptor ESRRA (estrogen related receptor alpha) is critical in mitochondrial biogenesis and macroautophagy/autophagy function; however, the roles of ESRRA in intestinal function remain uncharacterized. Herein we identified that ESRRA acts as a key regulator of intestinal homeostasis by amelioration of colonic inflammation through activation of autophagic flux and control of host gut microbiota. Esrra-deficient mice presented with increased susceptibility to dextran sodium sulfate (DSS)-induced colitis with upregulation of intestinal inflammation. In addition, esrra-null mice had depressed AMP-activated protein kinase phosphorylation (AMPK), lower levels of TFEB (transcription factor EB), and accumulation of SQSTM1/p62 (sequestosome 1) with defective mitochondria in intestinal tissues. Esrra-deficient mice showed distinct gut microbiota composition and significantly higher microbial diversity than wild-type (WT) mice. Cohousing or fecal microbiota transplantation from WT mice to Esrra-deficient mice ameliorated DSS-induced colitis severity. Importantly, patients with ulcerative colitis (UC) had significantly decreased ESRRA expression in intestinal mucosal tissues that correlated with disease activity, suggesting clinical relevance of ESRRA in UC. Taken together, our results show that ESRRA contributes to intestinal homeostasis through autophagy activation and gut microbiota control to protect the host from detrimental inflammation and dysfunctional mitochondria.Abbreviations: ABX, antibotics; AMPK, AMP-activated protein kinase; ATP5A1, ATP synthase, H+ transporting, mitochondrial F1 complex, alpha subunit 1; BECN1, beclin1, autophagy related, CCL, C-C motif chemokine ligand; CD, Crohn disease; CLDN, claudin; COX4I1, cytochrome c oxidase subunit 4I1; cKO, conditional knockout; cWT, conditional wild-type; CXCL, C-X-C motif chemokine ligand; DAI, disease activity index; DSS, dextran sodium sulfate; EGFP, enhanced green fluorescent protein; ESRR, estrogen related receptor; ESRRA, estrogen related receptor alpha; Esrra+/+, Esrra wild type; esrra-/-, esrra homozygous knockout; FMT, fecal microbiota transplantation; GABARAP, gamma-aminobutyric acid receptor associated protein; GSEA, gene set enrichment analysis; IBD, inflammatory bowel disease; IL, interleukin; KO, knockout; LAMP1, lysosomal-associated membrane protein 1; LCN2, lipocalin 2; LEfSe, linear discriminant analysis (LDA) effect size; LPS, lipopolysachharide; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; NDUFAB1, NADH: ubiquinone oxidoreductase subunit AB1; OCLN, occludin; OUT, operational taxonomic unit; OXPHOS, oxidative phosphorylation; PCoA, principal coordinate analysis; PPARGC1A, PPARG coactiva- tor 1 alpha; PRKAA, 5'-AMP-activated protein kinase catalytic subunit alpha; PTGS2/COX2, prostaglandin-endoperoxide synthase 2; RAB7, member RAS oncogene family; SDHB, succinate dehydrogenase complex, subunit B, iron sulfur (Ip); SQSTM1/p62, sequestosome 1; S100A9, S100 calcium binding protein A9 (calgranulin B); TCA, tricarboxylic acid; TFEB, transcription factor EB; TNF, tumor necrosis factor; UC, ulcerative colitis; UCP2, uncoupling protein 2 (mitochondrial, proton carrier); UQCRC1, ubiquinol-cytochrome c reductase core protein 1; UVRAG, UV radiation resistance associated gene; Vil1, villin; VPS11, VPS11, CORVET/HOPS core sub-unit; WT, wild type.