Gut microbiota from metabolic disease-resistant, macrophage-specific RIP140 knockdown mice improves metabolic phenotype and gastrointestinal integrity

Alteration of Gut Immunity and Microbiome in Mixed Granulocytic Asthma

Growing evidence suggests that there is an essential link between the gut and lungs. Asthma is a common chronic inflammatory disease and is considered a heterogeneous disease. While it has been documented that eosinophilic asthma affects gut immunity and the microbiome, the effect of other types of asthma on the gut environment has not been examined. In this study, we utilized an OVA/poly I:C-induced mixed granulocytic asthma model and found increased Tregs without significant changes in other inflammatory cells in the colon. Interestingly, an altered gut microbiome has been observed in a mixed granulocytic asthma model. We observed an increase in the relative abundance of the Faecalibaculum genus and Erysipelotrichaceae family, with a concomitant decrease in the relative abundance of the genera Candidatus arthromitus and Streptococcus. The altered gut microbiome leads to changes in the abundance of genes associated with microbial metabolism, such as glycolysis. We found that mixed granulocytic asthma mainly affects the gut microbial composition and metabolism, which may have important implications in the severity and development of asthma and gut immune homeostasis. This suggests that altered gut microbial metabolism may be a potential therapeutic target for patients with mixed granulocytic asthma.

Downregulating carnitine palmitoyl transferase 1 affects disease progression in the SOD1 G93A mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease characterized by death of motor neurons. The etiology and pathogenesis remains elusive despite decades of intensive research. Herein, we report that dysregulated metabolism plays a central role in the SOD1 G93A mouse model mimicking ALS. Specifically, we report that the activity of carnitine palmitoyl transferase 1 (CPT1) lipid metabolism is associated with disease progression. Downregulation of CPT1 activity by pharmacological and genetic methods results in amelioration of disease symptoms, inflammation, oxidative stress and mitochondrial function, whereas upregulation by high-fat diet or corticosterone results in a more aggressive disease progression. Finally, we show that downregulating CPT1 shifts the gut microbiota communities towards a protective phenotype in SOD1 G93A mice. These findings reveal that metabolism, and specifically CPT1 lipid metabolism plays a central role in the SOD1 G93A mouse model and shows that CPT1 might be a therapeutic target in ALS.

Cellular retinoic acid binding protein 1 protects mice from high-fat diet-induced obesity by decreasing adipocyte hypertrophy

Objectives

Obesity, an emerging global health issue, involves numerous factors; understanding its underlying mechanisms for prevention and therapeutics is urgently needed. Cellular retinoic acid binding protein 1 (Crabp1) knockout (CKO) mice exhibit an obese phenotype under normal diet feedings, which prompted us to propose that Crabp1 could play a role in modulating adipose tissue development/homeostasis. Studies were designed to elucidate the underlying mechanism of Crabp1’s action in reducing obesity.

Subjects/methods

In animal studies, 6 weeks old male wild type and CKO mice were fed with normal diet (ND) or high fat diet (HFD) for 10 weeks. Body weight and food intake were regularly monitored. Glucose tolerance test and biological parameters of plasma (glucose and insulin levels) were measured after 10 weeks of ND vs. HFD feedings. Visceral adipose tissues were collected for histological and molecular analyses to determine affected signaling pathways. In cell culture studies, the 3T3L1 adipocyte differentiation model was used to examine and validate relevant signaling pathways.

Results

CKO mice, compared to WT mice, gained more body weight, exhibited more elevated fasting plasma glucose levels, and developed more severe impaired glucose tolerance under both ND and HFD. Histological examination revealed readily increased adipocyte hypertrophy and adipose tissue inflammation under HFD feedings. In 3T3L1 adipocytes, Crabp1 silencing enhanced extracellular signal-regulated kinase 1/2 (ERK1/2) activation, accompanied by elevated markers and signaling pathways of lipid accumulation and adipocyte hypertrophy.

Conclusions

This study identifies Crabp1’s physiological role against the development of obesity. The protective function of CRABP1 is likely attributed to its classically proposed (canonical) activity as a trap for RA, which will reduce RA availability, thereby dampening RA-stimulated ERK1/2 activation and adipocyte hypertrophy. The results suggest Crabp1 as a potentially new therapeutic target in managing obesity and metabolic diseases.

Glyburide and retinoic acid synergize to promote wound healing by anti-inflammation and RIP140 degradation

Chronic inflammation underlies the development of metabolic diseases and individuals with metabolic disease often also suffer from delayed wound healing due to prolonged inflammation. Resolving inflammation provides a therapeutic strategy in treating metabolic diseases. We previously showed that during an anti-inflammatory response when macrophages were alternatively (M2) polarized, retinoic acid (RA) dramatically activated arginase 1 gene (Arg1), a gene crucial for wound healing. Here we report that a widely used sulfonylurea drug for type 2 diabetes mellitus (T2DM), glyburide, enhances the anti-inflammatory response and synergizes with RA to promote wound healing. Our data also delineate the mechanism underlying glyburide’s anti-inflammatory effect, which is to stimulate the degradation of a pro-inflammatory regulator, Receptor Interacting Protein 140 (RIP140), by activating Ca2+/calmodulin-dependent protein kinase II (CamKII) that triggers specific ubiquitination of RIP140 for degradation. By stimulating RIP140 degradation, glyburide enhances M2 polarization and anti-inflammation. Using a high-fat diet induced obesity mouse model to monitor wound healing effects, we provide a proof-of-concept for a therapeutic strategy that combining glyburide and RA can significantly improve wound healing. Mechanistically, this study uncovers a new mechanism of action of glyburide and a new pathway modulating RIP140 protein degradation that is mediated by CamKII signaling.

Innate immunity orchestrates adipose tissue homeostasis

Obesity is strongly associated with multiple diseases including insulin resistance, type 2 diabetes, cardiovascular diseases, fatty liver disease, neurodegenerative diseases and cancers, etc. Adipose tissue (AT), mainly brown AT (BAT) and white AT (WAT), is an important metabolic and endocrine organ that maintains whole-body homeostasis. BAT contributes to non-shivering thermogenesis in a cold environment; WAT stores energy and produces adipokines that fine-tune metabolic and inflammatory responses. Obesity is often characterized by over-expansion and inflammation of WAT where inflammatory cells/mediators are abundant, especially pro-inflammatory (M1) macrophages, resulting in chronic low-grade inflammation and leading to insulin resistance and metabolic complications. Macrophages constitute the major component of innate immunity and can be activated as a M1 or M2 (anti-inflammatory) phenotype in response to environmental stimuli. Polarized M1 macrophage causes AT inflammation, whereas polarized M2 macrophage promotes WAT remodeling into the BAT phenotype, also known as WAT browning/beiging, which enhances insulin sensitivity and metabolic health. This review will discuss the regulation of AT homeostasis in relation to innate immunity.