The endoplasmic reticulum stress sensor IRE1 regulates collagen secretion through the enforcement of the proteostasis factor P4HB/PDIA1 contributing to liver damage and fibrosis

Collagen is one the most abundant proteins and the main cargo of the secretory pathway, contributing to hepatic fibrosis and cirrhosis due to excessive deposition of extracellular matrix. Here we investigated the possible contribution of the unfolded protein response, the main adaptive pathway that monitors and adjusts the protein production capacity at the endoplasmic reticulum, to collagen biogenesis and liver disease. Genetic ablation of the ER stress sensor IRE1 reduced liver damage and diminished collagen deposition in models of liver fibrosis triggered by carbon tetrachloride (CCl ₄ ) administration or by high fat diet. Proteomic and transcriptomic profiling identified the prolyl 4-hydroxylase (P4HB, also known as PDIA1), which is known to be critical for collagen maturation, as a major IRE1-induced gene. Cell culture studies demonstrated that IRE1 deficiency results in collagen retention at the ER and altered secretion, a phenotype rescued by P4HB overexpression. Taken together, our results collectively establish a role of the IRE1/P4HB axis in the regulation of collagen production and its significance in the pathogenesis of various disease states.

Palmitic acid control of ciliogenesis modulates insulin signaling in hypothalamic neurons through an autophagy-dependent mechanism

Palmitic acid (PA) is significantly increased in the hypothalamus of mice, when fed chronically with a high-fat diet (HFD). PA impairs insulin signaling in hypothalamic neurons, by a mechanism dependent on autophagy, a process of lysosomal-mediated degradation of cytoplasmic material. In addition, previous work shows a crosstalk between autophagy and the primary cilium (hereafter cilium), an antenna-like structure on the cell surface that acts as a signaling platform for the cell. Ciliopathies, human diseases characterized by cilia dysfunction, manifest, type 2 diabetes, among other features, suggesting a role of the cilium in insulin signaling. Cilium depletion in hypothalamic pro-opiomelanocortin (POMC) neurons triggers obesity and insulin resistance in mice, the same phenotype as mice deficient in autophagy in POMC neurons. Here we investigated the effect of chronic consumption of HFD on cilia; and our results indicate that chronic feeding with HFD reduces the percentage of cilia in hypothalamic POMC neurons. This effect may be due to an increased amount of PA, as treatment with this saturated fatty acid in vitro reduces the percentage of ciliated cells and cilia length in hypothalamic neurons. Importantly, the same effect of cilia depletion was obtained following chemical and genetic inhibition of autophagy, indicating autophagy is required for ciliogenesis. We further demonstrate a role for the cilium in insulin sensitivity, as cilium loss in hypothalamic neuronal cells disrupts insulin signaling and insulin-dependent glucose uptake, an effect that correlates with the ciliary localization of the insulin receptor (IR). Consistently, increased percentage of ciliated hypothalamic neuronal cells promotes insulin signaling, even when cells are exposed to PA. Altogether, our results indicate that, in hypothalamic neurons, impairment of autophagy, either by PA exposure, chemical or genetic manipulation, cause cilia loss that impairs insulin sensitivity.

New emerging roles of Polycystin-2 in the regulation of autophagy

Polycystin-2 (PC2) is a calcium channel that can be found in the endoplasmic reticulum, the plasmatic membrane, and the primary cilium. The structure of PC2 is characterized by a highly ordered C-terminal tail with an EF-motif (calcium-binding domain) and a canonical coiled-coil domain (CCD; interaction domain), and its activity is regulated by interacting partners and post-translational modifications. Calcium mobilization into the cytosol by PC2 has been mainly associated with cell growth and differentiation, and therefore mutations or dysfunction of PC2 lead to renal and cardiac consequences. Interestingly, PC2-related pathologies are usually treated with rapamycin, an autophagy stimulator. Autophagy is an intracellular degradation process where recycling material is sequestered into autophagosomes and then hydrolyzed by fusion with a lysosome. Interestingly, several studies have provided evidence that PC2 may be required for autophagy, suggesting that PC2 maintains a physiologic catabolic state.

New Insights on the Role of Lipid Metabolism in the Metabolic Reprogramming of Macrophages

Macrophage activation is intimately linked to metabolic reprogramming. Inflammatory (M1) macrophages are able to sustain inflammatory responses and to kill pathogens, mostly by relying on aerobic glycolysis and fatty acid biosynthesis. Glycolysis is a fast way of producing ATP, and fatty acids serve as precursors for the synthesis of inflammatory mediators. On the opposite side, anti-inflammatory (M2) macrophages mediate the resolution of inflammation and tissue repair, switching their metabolism to fatty acid oxidation and oxidative phosphorylation. Over the years, this classical view has been challenged by recent discoveries pointing to a more complex metabolic network during macrophage activation. Lipid metabolism plays a critical role in the activation of both M1 and M2 macrophages. Recent evidence shows that fatty acid oxidation is also essential for inflammasome activation in M1 macrophages, and glycolysis is now known to fuel fatty acid oxidation in M2 macrophages. Ultimately, targeting lipid metabolism in macrophages can improve the outcome of metabolic diseases. Here, we review the main aspects of macrophage immunometabolism from the perspective of the metabolism of lipids. Building a reliable metabolic network during macrophage activation will bring us closer to targeting macrophages for improving human health.

Autophagy Regulates the Liver Clock and Glucose Metabolism by Degrading CRY1

The circadian clock coordinates behavioral and circadian cues with availability and utilization of nutrients. Proteasomal degradation of clock repressors, such as cryptochrome (CRY)1, maintains periodicity. Whether macroautophagy, a quality control pathway, degrades circadian proteins remains unknown. Here we show that circadian proteins BMAL1, CLOCK, REV-ERBα, and CRY1 are lysosomal targets, and that macroautophagy affects the circadian clock by selectively degrading CRY1. Autophagic degradation of CRY1, an inhibitor of gluconeogenesis, occurs in a diurnal window when rodents rely on gluconeogenesis, suggesting that CRY1 degradation is time-imprinted to maintenance of blood glucose. High-fat feeding accelerates autophagic CRY1 degradation and contributes to obesity-associated hyperglycemia. CRY1 contains several light chain 3 (LC3)-interacting region (LIR) motifs, which facilitate the interaction of cargo proteins with the autophagosome marker LC3. Using mutational analyses, we identified two distinct LIRs on CRY1 that exert circadian glycemic control by regulating CRY1 degradation, revealing LIRs as potential targets for controlling hyperglycemia.

Enhanced control of Mycobacterium tuberculosis extrapulmonary dissemination in mice by an arabinomannan-protein conjugate vaccine

Currently there are a dozen or so of new vaccine candidates in clinical trials for prevention of tuberculosis (TB) and each formulation attempts to elicit protection by enhancement of cell-mediated immunity (CMI). In contrast, most approved vaccines against other bacterial pathogens are believed to mediate protection by eliciting antibody responses. However, it has been difficult to apply this formula to TB because of the difficulty in reliably eliciting protective antibodies. Here, we developed capsular polysaccharide conjugates by linking mycobacterial capsular arabinomannan (AM) to either Mtb Ag85b or B. anthracis protective antigen (PA). Further, we studied their immunogenicity by ELISA and AM glycan microarrays and protection efficacy in mice. Immunization with either Abg85b-AM or PA-AM conjugates elicited an AM-specific antibody response in mice. AM binding antibodies stimulated transcriptional changes in Mtb. Sera from AM conjugate immunized mice reacted against a broad spectrum of AM structural variants and specifically recognized arabinan fragments. Conjugate vaccine immunized mice infected with Mtb had lower bacterial numbers in lungs and spleen, and lived longer than control mice. These findings provide additional evidence that humoral immunity can contribute to protection against Mtb.

Vaccine design in the TB field has been driven by the imperative of attempting to elicit strong cell-mediated responses. However, in recent decades evidence has accumulated that humoral immunity can protect against many intracellular pathogens through numerous mechanisms. In this work, we demonstrate that immunization with mycobacterial capsular arabinomannan (AM) conjugates elicited responses that contributed to protection against Mtb infection. We developed two different conjugates including capsular AM linked to the Mtb related protein Ag85b or the Mtb unrelated PA from B. anthracis and found that immunization with AM conjugates elicited antibody populations with different specificities. These surface-specific antibodies could directly modify the transcriptional profile and metabolism of mycobacteria. In addition, we observed a prolonged survival and a reduction in bacterial numbers in lungs and spleen in mice immunized with Ag85b-AM conjugates after infection with Mtb and that the presence of AM-binding antibodies was associated with modest prolongation in survival and a marked reduction in mycobacterial dissemination. Finally, we show that AM is antigenically variable and could potentially form the basis for a serological characterization of mycobacteria based on serotypes.

The Type of Growth Medium Affects the Presence of a Mycobacterial Capsule and Is Associated With Differences in Protective Efficacy of BCG Vaccination Against Mycobacterium tuberculosis

BACKGROUND

Bacillus Calmette-Guerin (BCG) vaccine is widely used for the prevention of tuberculosis, despite limited efficacy. Most immunological studies of BCG or Mycobacterium tuberculosis strains grow bacteria in the presence of detergent, which also strips the mycobacterial capsule. The impact of the capsule on vaccine efficacy has not been explored.

METHODS

We tested the influence of detergent in cultures of BCG and M. tuberculosis strains on the outcome of vaccination experiments on mice and transcriptional responses on M. tuberculosis

RESULTS

Vaccination of mice with encapsulated BCG promoted a more potent immune response relative to vaccination with unencapsulated BCG, including higher polysaccharide-specific capsule antibody titers, higher interferon γ and interleukin 17 splenic responses, and more multifunctional CD4(+) T cells. These differences correlated with variability in the bacterial burden in lung and spleen of mice infected with encapsulated or unencapsulated M. tuberculosis The combination of vaccination and challenge with encapsulated strains resulted in the greatest protection efficacy. The transcriptome of encapsulated M. tuberculosis was similar to that of starvation, hypoxia, stationary phase, or nonreplicating persistence.

CONCLUSIONS

The presence of detergent in growth media and a capsule on BCG were associated with differences in the outcome of vaccination, implying that these are important variables in immunological studies.

Chimeric mouse/human Fab antibodies that selectively binds to the surface of Mycobacterium tuberculosis (MPF6P.649)

The current diagnostic tools for Tuberculosis (TB) are time consuming and not suitable for point of care devices. Antibody-based diagnostic approaches could solve this issue. We have used antibody phage-display to isolate chimeric mouse/human Fab antibodies that binds to the surface of live Mycobacterium tuberculosis (Mtb). For that purpose, mice were immunized with live or heat killed (HK) Mtb and splenic mRNA was used to generate 2 phage-display Fab libraries. Several rounds of bio panning were performed against whole cell live and HK Mtb and a substraction round was performed against non-tuberculous Mycobacteria. Of the 24 clones analyzed we found 6 Fab-expressing phages that specifically bind to live Mtb over HK or non-tuberculous Mycobacteria. Further characterization of these Fab antibodies consisted of recombinant expression and purification in E coli and selective binding to Mtb-specific subcellular fractions. This is the first study on Mtb-specific Fab antibodies that specifically bind a live and virulent Mtb strain. These molecules could represent a good platform to set up highly specific TB biomarkers.

Improving immunity against mycobacteria by targeting iNKT cells in a partially humanized mouse model (VAC4P.1103)

Invariant Natural Killer T cells (iNKT cells) are a specialized group of T lymphocytes which modulate many aspects of immune responses. They co-express an invariant T cell receptor (TCR) which recognizes glycolipid antigens bound to the CD1d molecule. Although mouse and human CD1d are relatively conserved, there are differences in the abundance and responses of human and mouse iNKT cells, which may correlate with differences in CD1d function. Thus, the study of iNKT cell responses and their role in disease models requires a more “humanized” model to enable more accurate translation of results to human therapy. Here, by using a human CD1d knock-in mouse, which displays similar frequency and phenotype in their iNKT cells to humans, we have vaccinated with different strains of potential tuberculos (TB) vaccine candidates carrying different glycolipid iNKT cell ligands. Our results shown that hCD1d-KI iNKT cells are able to enhance TB-specific T cell responses. We have also identified novel glycolipds with an enhanced ability to induce multifunctional T cells. Our results suggest that human CD1d knock-in mice are a valuable tool to study iNKT cell-based therapies.