The phosphatidylinositol 3-phosphate-binding protein SNX4 controls ATG9A recycling and autophagy.

Late endosomes and lysosomes (endolysosomes) receive proteins and cargo from the secretory, endocytic and autophagic pathways. Although these pathways and the degradative processes of endolysosomes are well characterized, less is understood about protein traffic from these organelles. In this study, we demonstrate the direct involvement of the phosphatidylinositol 3-phosphate (PI3P)-binding SNX4 protein in membrane protein recycling from endolysosomes, and show that SNX4 is required for proper autophagic flux. We show that SNX4 mediates recycling of the lipid scramblase ATG9A, which drives expansion of nascent autophagosome membranes, from endolysosomes to early endosomes, from where ATG9A is recycled to the trans-Golgi network in a retromer-dependent manner. Upon siRNA-mediated depletion of SNX4 or the retromer component VPS35, we observed accumulation of ATG9A on endolysosomes and early endosomes, respectively. Moreover, starvation-induced autophagosome biogenesis and autophagic flux were inhibited when SNX4 was downregulated. We propose that proper ATG9A recycling by SNX4 sustains autophagy by preventing exhaustion of the available ATG9A pool.This article has an associated First Person interview with the first author of the paper.

Inactivation of C/ebp homologous protein-driven immune-metabolic interactions exacerbate obesity and adipose tissue leukocytosis.

Successful adaptation to periods of chronic caloric excess is a highly coordinated event that is critical to the survival and propagation of species. Transcription factor C/ebp homologous protein (Chop) is thought to be an important molecular mediator that integrates nutrient signals to endoplasmic reticulum (ER) stress and innate immune activation. Given that aberrant ER stress response is implicated in inducing metabolic inflammation and insulin resistance, we hypothesized that ER stress target gene Chop integrates immune and metabolic systems to adapt to chronic positive energy balance. Here we report that inactivation of Chop in mice fed a high fat diet led to significant increase in obesity caused by a reduction in energy expenditure without any change in food intake. Importantly, ablation of Chop does not induce metabolically healthy obesity, because Chop-deficient mice fed a high fat diet had increased hepatic steatosis with significantly higher insulin resistance. Quantification of adipose tissue leukocytosis revealed that elimination of Chop during obesity led to substantial increase in number of adipose tissue T and B lymphocytes. In addition, deficiency of Chop led to increase in total number of myeloid subpopulations like neutrophils and F4/80(+) adipose tissue macrophages without any alterations in the frequency of M1- or M2-like adipose tissue macrophages. Further investigation of inflammatory mechanisms revealed that ablation of Chop increases the sensitivity of macrophages to inflammasome-induced activation of IL-ß in macrophages. Our findings indicate that regulated expression of Chop during obesity is critical for adaptation to chronic caloric excess and maintenance of energy homeostasis via integration of metabolic and immune systems.

Determinants of humoral and cellular immune responses to three doses of mRNA SARS-CoV-2 vaccines in older adults: a longitudinal cohort study.

BACKGROUND: Older age is associated with poorer outcomes to COVID-19 infection. The Norwegian Institute of Public Health established a longitudinal cohort of adults aged 65-80 years to study the effects of the COVID-19 pandemic. Here we describe the characteristics of the cohort in general, and specifically the immune responses at baseline and after primary and booster vaccination in a subset of longitudinal blood samples, and the epidemiological factors affecting these responses. METHODS: 4551 participants were recruited, with humoral (n=299) and cellular (n=90) responses measured before vaccination and after two and three vaccine doses. Information on general health, infections, and vaccinations were obtained from questionnaires and national health registries. FINDINGS: Half of the participants had a chronic condition. 849 (18·7%) of 4551 were prefrail and 184 (4%) of 4551 were frail. 483 (10·6%) of 4551 had general activity limitations (scored with the Global Activity Limitation Index). After dose two, 295 (98·7%) of 299 participants were seropositive for anti-receptor binding domain IgG, and 210 (100%) of 210 participants after dose three. Spike-specific CD4 and CD8 T cell responses showed high heterogeneity after vaccination and responded to the alpha (B.1.1.7), delta (B.1.617.2), and omicron (B.1.1.529 or BA.1) variants of concern. Cellular responses to seasonal coronaviruses increased after SARS-CoV-2 vaccination. Heterologous prime boosting with mRNA vaccines was associated with the highest antibody (p=0·019) and CD4 T cell responses (p=0·003), and hypertension with lower antibody levels after three doses (p=0·04). INTERPRETATION: Most older adults, including those with comorbidities, generated good serological and cellular responses after two vaccine doses. Responses further improved after three doses, particularly after heterologous boosting. Vaccination also generated cross-reactive T cells against variants of concern and seasonal coronaviruses. Frailty was not associated with impaired immune responses, but hypertension might indicate reduced responsiveness to vaccines even after three doses. Individual differences identified through longitudinal sampling enables better prediction of the variability of vaccine responses, which can help guide future policy on the need for subsequent doses and their timing. FUNDING: Norwegian Institute of Public Health, Norwegian Ministry of Health, Research Council of Norway, and Coalition for Epidemic Preparedness Innovations.

T cell responses to SARS-CoV-2 vaccination differ by disease-modifying therapy for multiple sclerosis.

Immune responses in people with multiple sclerosis (pwMS) receiving disease-modifying therapies (DMTs) have been of significant interest throughout the COVID-19 pandemic. Lymphocyte-targeting immunotherapies, including anti-CD20 treatments and sphingosine-1-phosphate receptor (S1PR) modulators, attenuate Ab responses after vaccination. Evaluation of cellular responses after vaccination, therefore, is of particular importance in these populations. In this study, we used flow cytometry to analyze CD4 and CD8 T cell functional responses to SARS-CoV-2 spike peptides in healthy control study participants and pwMS receiving 5 different DMTs. Although pwMS receiving rituximab and fingolimod therapies had low Ab responses after both 2 and 3 vaccine doses, T cell responses in pwMS taking rituximab were preserved after a third vaccination, even when an additional dose of rituximab was administered between vaccine doses 2 and 3. PwMS taking fingolimod had low detectable T cell responses in peripheral blood. CD4 and CD8 T cell responses to SARS-CoV-2 variants of concern Delta and Omicron were lower than to the ancestral Wuhan-Hu-1 variant. Our results indicate the importance of assessing both cellular and humoral responses after vaccination and suggest that, even in the absence of robust Ab responses, vaccination can generate immune responses in pwMS.

Obesity increases the production of proinflammatory mediators from adipose tissue T cells and compromises TCR repertoire diversity: implications for systemic inflammation and insulin resistance.

Emerging evidence suggests that increases in activated T cell populations in adipose tissue may contribute toward obesity-associated metabolic syndrome. The present study investigates three unanswered questions: 1) Do adipose-resident T cells (ARTs) from lean and obese mice have altered cytokine production in response to TCR ligation?; 2) Do the extralymphoid ARTs possess a unique TCR repertoire compared with lymphoid-resident T cells and whether obesity alters the TCR diversity in specific adipose depots?; and 3) Does short-term elimination of T cells in epididymal fat pad without disturbing the systemic T cell homeostasis regulate inflammation and insulin-action during obesity? We found that obesity reduced the frequency of naive ART cells in s.c. fat and increased the effector-memory populations in visceral fat. The ARTs from diet-induced obese (DIO) mice had a higher frequency of IFN-gamma(+), granzyme B(+) cells, and upon TCR ligation, the ARTs from DIO mice produced increased levels of proinflammatory mediators. Importantly, compared with splenic T cells, ARTs exhibited markedly restricted TCR diversity, which was further compromised by obesity. Acute depletion of T cells from epididymal fat pads improved insulin action in young DIO mice but did not reverse obesity-associated feed forward cascade of chronic systemic inflammation and insulin resistance in middle-aged DIO mice. Collectively, these data establish that ARTs have a restricted TCR-Vbeta repertoire, and T cells contribute toward the complex proinflammatory microenvironment of adipose tissue in obesity. Development of future long-term T cell depletion protocols specific to visceral fat may represent an additional strategy to manage obesity-associated comorbidities.

Immune responses in Omicron SARS-CoV-2 breakthrough infection in vaccinated adults.

The SARS-CoV-2 Omicron variant has more than 15 mutations in the receptor binding domain of the Spike protein enabling increased transmissibility and viral escape from antibodies in vaccinated individuals. It is unclear how vaccine immunity protects against Omicron infection. Here we show that vaccinated participants at a super-spreader event have robust recall response of humoral and pre-existing cellular immunity induced by the vaccines, and an emergent de novo T cell response to non-Spike antigens. Individuals with Omicron SARS-CoV-2 breakthrough infections have significantly increased activated SARS-CoV-2 wild type Spike-specific cytotoxic T cells, activated follicular helper (TFH) cells, functional T cell responses, boosted humoral responses, and rapid release of Spike and RBD-specific IgG+ B cell plasmablasts and memory B cells into circulation. Omicron breakthrough infection affords significantly increased de novo memory T cell responses to non-Spike viral antigens. Concerted T and B cell responses may provide durable and broad immunity.

Loss of Nucleobindin-2 Causes Insulin Resistance in Obesity without Impacting Satiety or Adiposity.

Inducers of satiety are drug targets for weight loss to mitigate obesity-associated diseases. Nucleobindin-2 (Nucb2) is thought to be post-translationally processed into bioactive nesfatin-1 peptide, which reportedly induces satiety, causes weight loss, and thus improves insulin sensitivity. Here, we show that deletion of Nucb2 did not affect food intake or adiposity and, instead, caused insulin resistance in mice fed a high-fat diet. In addition, ablation of Nucb2 in orexigenic hypothalamic Agrp neurons did not affect food intake, and nesfatin-1 was detectable in serum, despite global deletion of Nucb2 protein. Upon high-fat diet feeding, the loss of Nucb2 exacerbated metabolic inflammation in adipose tissue macrophages in an NFκB-dependent manner without inducing classical M1 or alternative M2-like macrophage polarization. Furthermore, the loss of Nucb2 in myeloid cells but not in adipocytes mediated the insulin resistance in response to a high-fat diet. Our study reveals that Nucb2 links metabolic inflammation to insulin resistance without affecting weight gain and food intake.

Quantification of adipose tissue leukocytosis in obesity.

The infiltration of immune cell subsets in adipose tissue termed "adipose tissue leukocytosis" is a critical event in the development of chronic inflammation and obesity-associated comorbidities. Given that a significant proportion of cells in adipose tissue of obese patients are of hematopoietic lineage, the distinct adipose depots represent an uncharacterized immunological organ that can impact metabolic functions. Here, we describe approaches to characterize and isolate leukocytes from the complex adipose tissue microenvironment, to aid mechanistic studies to better understand the role of specific pattern recognition receptors (PRRs) such as inflammasomes in adipose-immune cross talk.

Canonical Nlrp3 inflammasome links systemic low-grade inflammation to functional decline in aging.

Despite a wealth of clinical data showing an association between inflammation and degenerative disorders in the elderly, the immune sensors that causally link systemic inflammation to aging remain unclear. Here we detail a mechanism by which the Nlrp3 inflammasome controls systemic low-grade age-related "sterile" inflammation in both periphery and brain independently of the noncanonical caspase-11 inflammasome. Ablation of Nlrp3 inflammasome protected mice from age-related increases in the innate immune activation, alterations in CNS transcriptome, and astrogliosis. Consistent with the hypothesis that systemic low-grade inflammation promotes age-related degenerative changes, the deficient Nlrp3 inflammasome-mediated caspase-1 activity improved glycemic control and attenuated bone loss and thymic demise. Notably, IL-1 mediated only Nlrp3 inflammasome-dependent improvement in cognitive function and motor performance in aged mice. These studies reveal Nlrp3 inflammasome as an upstream target that controls age-related inflammation and offer an innovative therapeutic strategy to lower Nlrp3 activity to delay multiple age-related chronic diseases.

The Nlrp3 inflammasome promotes age-related thymic demise and immunosenescence.

The collapse of thymic stromal cell microenvironment with age and resultant inability of the thymus to produce naive T cells contributes to lower immune-surveillance in the elderly. Here we show that age-related increase in 'lipotoxic danger signals' such as free cholesterol (FC) and ceramides, leads to thymic caspase-1 activation via the Nlrp3 inflammasome. Elimination of Nlrp3 and Asc, a critical adaptor required for inflammasome assembly, reduces age-related thymic atrophy and results in an increase in cortical thymic epithelial cells, T cell progenitors and maintenance of T cell repertoire diversity. Using a mouse model of irradiation and hematopoietic stem cell transplantation (HSCT), we show that deletion of the Nlrp3 inflammasome accelerates T cell reconstitution and immune recovery in middle-aged animals. Collectively, these data demonstrate that lowering inflammasome-dependent caspase-1 activation increases thymic lymphopoiesis and suggest that Nlrp3 inflammasome inhibitors may aid the re-establishment of a diverse T cell repertoire in middle-aged or elderly patients undergoing HSCT.

Elimination of the NLRP3-ASC inflammasome protects against chronic obesity-induced pancreatic damage.

Clinical evidence that the blockade of IL-1ß in type-2 diabetic patients improves glycemia is indicative of an autoinflammatory mechanism that may trigger adiposity-driven pancreatic damage. IL-1ß is a key contributor to the obesity-induced inflammation and subsequent insulin resistance, pancreatic ß-cell dysfunction, and the onset of type 2 diabetes. Our previous studies demonstrated that the ceramides activate the Nod-like receptor family, pyrin domain containing 3 (Nlrp3) inflammasome to cause the generation of mature IL-1ß and ablation of the Nlrp3 inflammasome in diet-induced obesity improves insulin signaling. However, it remains unclear whether the posttranslational processing of active IL-1ß in pancreas is regulated by the NLRP3 inflammasome or whether the alternate mechanisms play a dominant role in chronic obesity-induced pancreatic ß-cell exhaustion. Here we show that loss of ASC, a critical adaptor required for the assembly of the NLRP3 and absent in melanoma 2 inflammasome substantially improves the insulin action. Surprisingly, despite lower insulin resistance in the chronically obese NLRP3 and ASC knockout mice, the insulin levels were substantially higher when the inflammasome pathway was eliminated. The obesity-induced increase in maturation of pancreatic IL-1ß and pancreatic islet fibrosis was dependent on the NLRP3 inflammasome activation. Furthermore, elimination of NLRP3 inflammasome protected the pancreatic ß-cells from cell death caused by long-term high-fat feeding during obesity with significant increase in the size of the islets of Langerhans. Collectively, this study provides direct in vivo evidence that activation of the NLRP3 inflammasome in diet-induced obesity is a critical trigger in causing pancreatic damage and is an important mechanism of progression toward type 2 diabetes.

The NLRP3 inflammasome instigates obesity-induced inflammation and insulin resistance.

The emergence of chronic inflammation during obesity in the absence of overt infection or well-defined autoimmune processes is a puzzling phenomenon. The Nod-like receptor (NLR) family of innate immune cell sensors, such as the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (Nlrp3, but also known as Nalp3 or cryopyrin) inflammasome are implicated in recognizing certain nonmicrobial originated 'danger signals' leading to caspase-1 activation and subsequent interleukin-1ß (IL-1ß) and IL-18 secretion. We show that calorie restriction and exercise-mediated weight loss in obese individuals with type 2 diabetes is associated with a reduction in adipose tissue expression of Nlrp3 as well as with decreased inflammation and improved insulin sensitivity. We further found that the Nlrp3 inflammasome senses lipotoxicity-associated increases in intracellular ceramide to induce caspase-1 cleavage in macrophages and adipose tissue. Ablation of Nlrp3 in mice prevents obesity-induced inflammasome activation in fat depots and liver as well as enhances insulin signaling. Furthermore, elimination of Nlrp3 in obese mice reduces IL-18 and adipose tissue interferon-γ (IFN-γ) expression, increases naive T cell numbers and reduces effector T cell numbers in adipose tissue. Collectively, these data establish that the Nlrp3 inflammasome senses obesity-associated danger signals and contributes to obesity-induced inflammation and insulin resistance.