Defective expression of SIRT1 contributes to sustain inflammatory pathways in the gut

Transforming Growth Factor-β1/Smad7 in Intestinal Immunity, Inflammation, and Cancer

In physiological conditions, the activity of the intestinal immune system is tightly regulated to prevent tissue-damaging reactions directed against components of the luminal flora. Various factors contribute to maintain immune homeostasis and diminished production and/or function of such molecules trigger and/or propagate detrimental signals, which can eventually lead to chronic colitis and colon cancer. One such a molecule is transforming growth factor-β1 (TGF-β1), a cytokine produced by many inflammatory and non-inflammatory cells and targeting virtually all the intestinal mucosal cell types, with the down-stream effect of activating intracellular Smad2/3 proteins and suppressing immune reactions. In patients with inflammatory bowel diseases (IBD), there is defective TGF-β1/Smad signaling due to high Smad7, an inhibitor of TGF-β1 activity. Indeed, knockdown of Smad7 with a specific antisense oligonucleotide restores endogenous TGF-β1 activity, thereby inhibiting inflammatory pathways in patients with IBD and colitic mice. Consistently, mice over-expressing Smad7 in T cells develop severe intestinal inflammation in various experimental models. Smad7 expression is also upregulated in colon cancer cells, in which such a protein controls positively intracellular pathways that sustain neoplastic cell growth and survival. We here review the role of TGF-β1 and Smad7 in intestinal immunity, inflammation, and cancer.

One-pot synthesis of biologically active 1,2,3-trisubstituted pyrrolo[2,3-b]quinoxalines through a palladium-catalyzed reaction with internal alkyne moieties

Synthesis of 2,3-disubstituted 1-alkylpyrrolo[2,3-b]quinoxalines was accomplished through the reaction of 3-chloroquinoxalin-2-amines with internal alkynes in the presence of Pd(OAc)[Formula: see text], NaOAc, and KOtBu in DMSO. This method afforded desired pyrrolo[2,3-b]quinoxalines in 65-92% reaction yields. The minimum inhibition concentration and minimum bactericidal concentration determinations against Micrococcus luteus and Pseudomonas aeruginosa revealed that some of the synthesized compounds showed the same values compared to tetracycline. These compounds could be used in the future research for the development of new antibiotics.

CAY10591, a SIRT1 activator, suppresses cell growth, invasion, and migration in gingival epithelial carcinoma cells

SIRT1 is a NAD-dependent histone deacetylase that is important in a wide variety of physiological and pathophysiological processes. Although many studies have examined the relationship between SIRT1 and cancer, the role of SIRT1 in tumor malignancy is controversial. Here, we examined the effects of the SIRT1 activator CAY10591 in gingival epithelial carcinoma Ca9-22 cells. CAY10591 treatment dose- and time-dependently increased SIRT1 level and activity. The treatment decreased cell growth and induced cell-cycle repressor p21 levels. In addition, dimethyl sulfoxide significantly reduced cellular invasion and migration, and CAY10591 enhanced this decrease. Quantitative PCR analysis showed that CAY10591 decreased expression of several invasion/migration promoter genes and induced repressor genes. Our findings suggest that CAY10591 suppresses cell growth and invasion/migration activity in gingival squamous cell carcinoma Ca9-22 cells.

NLRX1 Modulates Immunometabolic Mechanisms Controlling the Host-Gut Microbiota Interactions during Inflammatory Bowel Disease

Interactions among the gut microbiome, dysregulated immune responses, and genetic factors contribute to the pathogenesis of inflammatory bowel disease (IBD). Nlrx1^−/− mice have exacerbated disease severity, colonic lesions, and increased inflammatory markers. Global transcriptomic analyses demonstrate enhanced mucosal antimicrobial defense response, chemokine and cytokine expression, and epithelial cell metabolism in colitic Nlrx1^−/− mice compared to wild-type (WT) mice. Cell-specificity studies using cre-lox mice demonstrate that the loss of NLRX1 in intestinal epithelial cells (IEC) recapitulate the increased sensitivity to DSS colitis observed in whole body Nlrx1^−/− mice. Further, organoid cultures of Nlrx1^−/− and WT epithelial cells confirm the altered patterns of proliferation, amino acid metabolism, and tight junction expression. These differences in IEC behavior can impact the composition of the microbiome. Microbiome analyses demonstrate that colitogenic bacterial taxa such as Veillonella and Clostridiales are increased in abundance in Nlrx1^−/− mice and in WT mice co-housed with Nlrx1^−/− mice. The transfer of an Nlrx1^−/−-associated gut microbiome through co-housing worsens disease in WT mice confirming the contributions of the microbiome to the Nlrx1^−/− phenotype. To validate NLRX1 effects on IEC metabolism mediate gut–microbiome interactions, restoration of WT glutamine metabolic profiles through either exogenous glutamine supplementation or administration of 6-diazo-5-oxo-l-norleucine abrogates differences in inflammation, microbiome, and overall disease severity in Nlrx1^−/− mice. The influence NLRX1 deficiency on SIRT1-mediated effects is identified to be an upstream controller of the Nlrx1^−/− phenotype in intestinal epithelial cell function and metabolism. The altered IEC function and metabolisms leads to changes in barrier permeability and microbiome interactions, in turn, promoting greater translocation and inflammation and resulting in an increased disease severity. In conclusion, NLRX1 is an immunoregulatory molecule and a candidate modulator of the interplay between mucosal inflammation, metabolism, and the gut microbiome during IBD.

Linking the biological underpinnings of depression: Role of mitochondria interactions with melatonin, inflammation, sirtuins, tryptophan catabolites, DNA repair and oxidative and nitrosative stress, with consequences for classification and cognition

The pathophysiological underpinnings of neuroprogressive processes in recurrent major depressive disorder (rMDD) are reviewed. A wide array of biochemical processes underlie MDD presentations and their shift to a recurrent, neuroprogressive course, including: increased immune-inflammation, tryptophan catabolites (TRYCATs), mitochondrial dysfunction, aryl hydrocarbonn receptor activation, and oxidative and nitrosative stress (O&NS), as well as decreased sirtuins and melatonergic pathway activity. These biochemical changes may have their roots in central, systemic and/or peripheral sites, including in the gut, as well as in developmental processes, such as prenatal stressors and breastfeeding consequences. Consequently, conceptualizations of MDD have dramatically moved from simple psychological and central biochemical models, such as lowered brain serotonin, to a conceptualization that incorporates whole body processes over a lifespan developmental timescale. However, important hubs are proposed, including the gut-brain axis, and mitochondrial functioning, which may provide achievable common treatment targets despite considerable inter-individual variability in biochemical changes. This provides a more realistic model of the complexity of MDD and the pathophysiological processes that underpin the shift to rMDD and consequent cognitive deficits. Such accumulating data on the pathophysiological processes underpinning MDD highlights the need in psychiatry to shift to a classification system that is based on biochemical processes, rather than subjective phenomenology.

Sirtuin-6 preserves R-spondin-1 expression and increases resistance of intestinal epithelium to injury in mice

Sirtuin-6 (Sirt6) is a critical epigenetic regulator, but its function in the gut is unknown. Here, we studied the role of intestinal epithelial Sirt6 in colitis-associated intestinal epithelial injury. We found that Sirt6, which is predominantly expressed in epithelial cells in intestinal crypts, is decreased in colitis in both mice and humans. Colitis-derived inflammatory mediators including interferon-γ and reactive oxygen species strongly inhibited Sirt6 protein expression in young adult mouse colonocyte (YAMC) cells. The susceptibility of the cells to injurious insults was increased after knockdown of Sirt6 expression. In contrast, YAMC cells with Sirt6 overexpression exhibited more resistance to injurious insult. Furthermore, intestinal epithelial-specific Sirt6 (Sirt6IEC-KO) knockout mice exhibited greater susceptibility to dextran sulfate sodium (DSS)-induced colitis. RNA sequencing transcriptome analysis revealed that inflammatory mediators such as tumor necrosis factor (TNF)-α suppressed expression of R-spondin-1 (Rspo1, a critical growth factor for intestinal epithelial cells) in Sirt6-silenced YAMC cells in vitro. In addition, lipopolysaccharide was found to inhibit colonic Rspo1 expression in Sirt6IEC-KO mice but not their control littermates. Furthermore, Sirt6IEC-KO mice with DSS-induced colitis also exhibited in a significant decrease in Rspo1 expression in colons. In vitro, knockdown of Rspo1 attenuated the effect of ectopic expression of Sirt6 on protection of YAMC cells against cell death challenges. In conclusion, Sirt6 plays an important role in protecting intestinal epithelial cells against inflammatory injury in a mechanism associated with preserving Rspo1 levels in the cells.

Intestinal Epithelial Sirtuin 1 Regulates Intestinal Inflammation During Aging in Mice by Altering the Intestinal Microbiota

BACKGROUND & AIMS

Intestinal epithelial homeostasis is maintained by complex interactions among epithelial cells, commensal gut microorganisms, and immune cells. Disruption of this homeostasis is associated with disorders such as inflammatory bowel disease (IBD), but the mechanisms of this process are not clear. We investigated how Sirtuin 1 (SIRT1), a conserved mammalian NAD+-dependent protein deacetylase, senses environmental stress to alter intestinal integrity.

METHODS

We performed studies of mice with disruption of Sirt1 specifically in the intestinal epithelium (SIRT1 iKO, villin-Cre+, Sirt1flox/flox mice) and control mice (villin-Cre-, Sirt1flox/flox) on a C57BL/6 background. Acute colitis was induced in some mice by addition of 2.5% dextran sodium sulfate to drinking water for 5-9 consecutive days. Some mice were given antibiotics via their drinking water for 4 weeks to deplete their microbiota. Some mice were fed with a cholestyramine-containing diet for 7 days to sequester their bile acids. Feces were collected and proportions of microbiota were analyzed by 16S rRNA amplicon sequencing and quantitative PCR. Intestines were collected from mice and gene expression profiles were compared by microarray and quantitative PCR analyses. We compared levels of specific mRNAs between colon tissues from age-matched patients with ulcerative colitis (n=10) vs without IBD (n=8, controls).

RESULTS

Mice with intestinal deletion of SIRT1 (SIRT1 iKO) had abnormal activation of Paneth cells starting at the age of 5-8 months, with increased activation of NF-κB, stress pathways, and spontaneous inflammation at 22-24 months of age, compared with control mice. SIRT1 iKO mice also had altered fecal microbiota starting at 4-6 months of age compared with control mice, in part because of altered bile acid metabolism. Moreover, SIRT1 iKO mice with defective gut microbiota developed more severe colitis than control mice. Intestinal tissues from patients with ulcerative colitis expressed significantly lower levels of SIRT1 mRNA than controls. Intestinal tissues from SIRT1 iKO mice given antibiotics, however, did not have signs of inflammation at 22-24 months of age, and did not develop more severe colitis than control mice at 4-6 months.

CONCLUSIONS

In analyses of intestinal tissues, colitis induction, and gut microbiota in mice with intestinal epithelial disruption of SIRT1, we found this protein to prevent intestinal inflammation by regulating the gut microbiota. SIRT1 might therefore be an important mediator of host-microbiome interactions. Agents designed to activate SIRT1 might be developed as treatments for IBDs.

The Crosstalk between the Gut Microbiota and Mitochondria during Exercise

Many physiological changes occur in response to endurance exercise in order to adapt to the increasing energy needs, mitochondria biogenesis, increased reactive oxygen species (ROS) production and acute inflammatory responses. Mitochondria are organelles within each cell that are crucial for ATP production and are also a major producer of ROS and reactive nitrogen species during intense exercise. Recent evidence shows there is a bidirectional interaction between mitochondria and microbiota. The gut microbiota have been shown to regulate key transcriptional co-activators, transcription factors and enzymes involved in mitochondrial biogenesis such as PGC-1α, SIRT1, and AMPK genes. Furthermore, the gut microbiota and its metabolites, such as short chain fatty acids and secondary bile acids, also contribute to host energy production, ROS modulation and inflammation in the gut by attenuating TNFα- mediated immune responses and inflammasomes such as NLRP3. On the other hand, mitochondria, particularly mitochondrial ROS production, have a crucial role in regulating the gut microbiota via modulating intestinal barrier function and mucosal immune responses. Recently, it has also been shown that genetic variants within the mitochondrial genome, could affect mitochondrial function and therefore the intestinal microbiota composition and activity. Diet is also known to dramatically modulate the composition of the gut microbiota. Therefore, studies targeting the gut microbiota can be useful for managing mitochondrial related ROS production, pro-inflammatory signals and metabolic limits in endurance athletes.

Resolution of inflammation in inflammatory bowel disease

Treatment of inflammatory bowel disease at present mainly targets mediators of inflammation to stop or suppress pro-inflammatory processes. Typical examples are steroids, suppression of T cells by thioguanine nucleotides, or antibodies against cytokines such as tumour necrosis factor, interleukin 12, or interleukin 23. In addition to suppression of inflammation, development of therapeutic strategies that support resolution of inflammation or that actively resolve inflammation might be desirable. Resolution of inflammation is now seen as an active process involving specific mediators (eg, lipid mediators or specific cytokines) that is mandatory to restore organ function and completely shut down inflammation. The molecular pathways involved in resolution of inflammation have been investigated in recent years and could be adopted in treatment strategies for inflammatory bowel disease. Among these approaches are anti-integrin strategies and means to produce or locally increase restitution or resolution factors, such as restoration of the activity of transforming growth factor-β by anti-SMAD7 antisense oligonucleotides. The potential role of inflammation-resolving lipid mediators (eg, resolvins), however, still warrants further study and clinical development. This Review focuses on the specific role of active resolution of inflammation in inflammatory bowel disease pathophysiology. Potential therapeutic targets based on these pathways are also discussed.

Sirt1 expression is associated with CD31 expression in blood cells from patients with chronic obstructive pulmonary disease

Background

Cigarette smoke induced oxidative stress has been shown to reduce silent information regulator 1 (Sirt1) levels in lung tissue from smokers and patients with COPD patients. Sirt1 is known to inhibit endothelial senescence and may play a protective role in vascular cells. Endothelial progenitor cells (EPCs) are mobilized into circulation under various pathophysiological conditions, and are thought to play an important role in tissue repair in chronic obstructive lung disease (COPD). Therefore, Sirt1 and EPC-associated mRNAs were measured in blood samples from patients with COPD and from cultured CD34⁺ progenitor cells to examine whether these genes are associated with COPD development.

Methods

This study included 358 patients with a smoking history of more than 10 pack-years. RNA was extracted from blood samples and from CD34⁺ progenitor cells treated with cigarette smoke extract (CSE), followed by assessment of CD31, CD34, Sirt1 mRNA, miR-34a, and miR-126-3p expression by real-time RT-PCR.

Results

The expression of CD31, CD34, Sirt1 mRNAs, and miR-126-3p decreased and that of miR-34a increased in moderate COPD compared with that in control smokers. However, no significant differences in these genes were observed in blood cells from patients with severe COPD compared with those in control smokers. CSE significantly decreased Sirt1 and increased miR-34a expression in cultured progenitor cells.

Conclusion

Sirt1 expression in blood cells from patients with COPD could be a biomarker for disease stability in patients with moderate COPD. MiR-34a may participate in apoptosis and/or senescence of EPCs in smokers. Decreased expression of CD31, CD34, and miR-126-3p potentially represents decreased numbers of EPCs in blood cell from patients with COPD.

SIRT1 inhibits inflammatory response partly through regulation of NLRP3 inflammasome in vascular endothelial cells

Emerging evidence has indicated that vascular endothelial cells (ECs) not only form the barrier between blood and the vessel wall but also serve as conditional innate immune cells. Our previous study found that SIRT1, a class III histone deacetylase, inhibits the inflammatory response in ECs. Recent studies revealed that SIRT1 also participates in the modulation of immune responses. Although the NLRP3 inflammasome is known to be a crucial component of the innate immune system, there is no direct evidence demonstrating the anti-inflammatory effect of SIRT1 on ECs through the NLRP3 inflammasome. In this study, we observed that lipopolysaccharide (LPS) and adenosine triphosphate (ATP) triggered the activation of NLRP3 inflammasome in human umbilical vein ECs (HUVECs). Moreover, SIRT1 expression was reduced in HUVECs stimulated with LPS and ATP. SIRT1 activator inhibited the expression of monocyte chemotactic protein-1 (MCP-1) and C-reactive protein (CRP), whereas SIRT1 knockdown resulted in significant increases in MCP-1 and CRP levels in HUVECs stimulated with LPS and ATP. Importantly, the lack of SIRT1 enhanced NLRP3 inflammasome activation and subsequent caspase-1 cleavage. On the other hand, NLRP3 siRNA blocked the activation of the NLRP3 inflammasome in HUVECs stimulated with LPS plus ATP. Further study revealed that NLRP3 inflammasome blockade significantly reduced MCP-1 and CRP production in HUVECs. In vivo studies indicated that implantation of the periarterial carotid collar inhibited arterial SIRT1 expression in rabbits. Meanwhile, treatment with a SIRT1 activator decreased the expression levels of MCP-1 and CRP in collared arteries and the interleukin (IL)-1β level in serum. Taken together, these findings indicate that NLRP3 inflammasome activation promoted endothelial inflammation and that SIRT1 inhibits the inflammatory response partly through regulation of the NLRP3 inflammasome in ECs.

Mongersen, an oral Smad7 antisense oligonucleotide, in patients with active Crohn's disease

In Crohn's disease (CD), the tissue-damaging inflammation is sustained by defects of counter-regulatory mechanisms, which normally inhibit immune-inflammatory signals and promote repair of mucosal injury. In particular, in inflamed gut of CD patients there are elevated levels of Smad7, an intracellular protein that inhibits the function of transforming growth factor (TGF)-β1. Knockdown of Smad7 with a specific antisense oligonucleotide, named mongersen, restores TGF-β1 activity thus leading to suppression of inflammatory pathways and resolution of colitis in mice. Consistently, oral administration of mongersen to patients with active CD induces clinical remission. In this article, we review the available data supporting the pathogenic role of Smad7 in CD and discuss the results of recent phase I and II trials assessing the efficacy and safety of mongersen in CD patients.

WISP1 Is Increased in Intestinal Mucosa and Contributes to Inflammatory Cascades in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is mainly characterized by intestinal tissue damage, which is caused by excessive autoimmune responses poorly controlled by corresponding regulatory mechanisms. WISP1, which belongs to the CCN protein family, is a secreted matricellular protein regulating several inflammatory pathways, such as Wnt/β-catenin pathway, and has been reported in several diseases including cancer. Here we examined the expression, regulatory mechanisms, and functions of WISP1 in IBD. WISP1 mRNA and protein expression was upregulated in colonic biopsies and lamina propria mononuclear cells (LPMC) of IBD patients compared with those of healthy controls. Tumor necrosis factor- (TNF-) α induced WISP1 expression in LPMC from healthy controls. Consistently, WISP1 mRNA expression was downregulated in colonic biopsies from IBD patients who had achieved clinical remission with infliximab (IFX). Furthermore, WISP1 expression was also found to be increased in colons from 2,4,6-trinitrobenzenesulfonic acid- (TNBS-) induced mice compared with those from control mice. Further studies confirmed that administration of rWISP1 could aggravate TNBS-induced colitis in vivo. Therefore, we concluded that WISP1 is increased in IBD and contributes to the proinflammatory cascades in the gut.

In Patients with Coronary Artery Disease and Type 2 Diabetes, SIRT1 Expression in Circulating Mononuclear Cells Is Associated with Levels of Inflammatory Cytokines but Not with Coronary Lesions

While SIRT1 is significantly associated with atherosclerosis and diabetic complications, its relevance to coronary lesions in patients with coronary artery disease and type 2 diabetes has not been specifically investigated. Thus, we assessed SIRT1 expression in peripheral blood mononuclear cells in these patients. We found that SIRT1 expression did not significantly correlate with syntax scores from coronary angiography (p > 0.05). Notably, plasma levels of the inflammatory cytokines tumor necrosis factor-α, monocyte chemoattractant protein-1, and high-sensitivity C-reactive protein were markedly higher in diabetic patients (p < 0.05). In addition, SIRT1 expression was negatively correlated with levels of these cytokines, as well as that of interleukin-6 (p < 0.05). In summary, the data indicate that SIRT1 expression in peripheral blood mononuclear cells is significantly correlated with inflammatory cytokines levels in patients with coronary artery disease and type 2 diabetes but not with the severity of coronary lesions.

Pathogenic aspects and therapeutic avenues of intestinal fibrosis in Crohn's disease

In Crohn's disease, one of the two major forms of inflammatory bowel diseases in human beings, persistent and chronic inflammation promotes fibrotic processes thereby facilitating formation of strictures, the most common indication for surgical intervention in this disorder. The pathogenesis of Crohn's disease-associated fibrosis is not fully understood, but variants of genes involved in the recognition of microbial components/products [e.g. CARD15 (caspase-activating recruitment domain 15) and ATG16L1 (autophagy-related 16-like 1)] are associated with this phenotype, and experimental evidence suggests that intestinal fibrosis results from an altered balance between deposition of ECM (extracellular matrix) and degradation of ECM by proteases. Studies have also contributed to identify the main phenotypic and functional alterations of cells involved in the fibrogenic process, as well as molecules that stimulate such cells to produce elevated amounts of collagen and other ECM-related proteins. In the present review, we assess the current knowledge about cellular and molecular mediators of intestinal fibrosis and describe results of recent studies aimed at testing the preventive/therapeutic effect of compounds in experimental models of intestinal fibrosis.

The TGF-β/Smad System in IBD Pathogenesis

In Crohn's disease and ulcerative colitis, the tissue-damaging destructive immune response is sustained by defects of counterregulatory mechanisms, which normally attenuate inflammatory pathways and promote repair of mucosal injury. One such mechanism involves transforming growth factor-β1 (TGF-β1), a cytokine that is produced by multiple cell types and targets both immune and nonimmune cells. Both in vitro and in vivo studies strongly support the role of TGF-β1 as a negative regulator of mucosal inflammation and indicate that defective production/activity of this cytokine can lead to the development of or exacerbate colitis. Interestingly, in the inflamed intestine of patients with inflammatory bowel disease, TGF-β1 expression is upregulated but TGF-β1-mediated immunosuppression is markedly impaired because of high Smad7, an intracellular inhibitor of TGF-β1-associated signaling. Consistently, knockdown of Smad7 with a specific antisense oligonucleotide restores TGF-β1 activity, thus leading to decreased production of inflammatory cytokines in both colitic mice and inflammatory bowel disease patients and attenuates clinical activity in Crohn's disease patients. In this article, we review data supporting the role of Smad7 in the pathogenesis of inflammatory bowel disease and discuss whether inhibition of Smad7 is therapeutically useful in Crohn's disease and how the benefit/risk of such an intervention should be monitored in the patients.

Palmitate Inhibits SIRT1-Dependent BMAL1/CLOCK Interaction and Disrupts Circadian Gene Oscillations in Hepatocytes

Elevated levels of serum saturated fatty acid palmitate have been shown to promote insulin resistance, increase cellular ROS production, and trigger cell apoptosis in hepatocytes during the development of obesity. However, it remains unclear whether palmitate directly impacts the circadian clock in hepatocytes, which coordinates nutritional inputs and hormonal signaling with downstream metabolic outputs. Here we presented evidence that the molecular clock is a novel target of palmitate in hepatocytes. Palmitate exposure at low dose inhibits the molecular clock activity and suppresses the cyclic expression of circadian targets including Dbp, Nr1d1 and Per2 in hepatocytes. Palmitate treatment does not seem to alter localization or reduce protein expression of BMAL1 and CLOCK, the two core components of the molecular clock in hepatocytes. Instead, palmitate destabilizes the protein-protein interaction between BMAL1-CLOCK in a dose and time-dependent manner. Furthermore, we showed that SIRT1 activators could reverse the inhibitory action of palmitate on BMAL1-CLOCK interaction and the clock gene expression, whereas inhibitors of NAD synthesis mimic the palmitate effects on the clock function. In summary, our findings demonstrated that palmitate inhibits the clock function by suppressing SIRT1 function in hepatocytes.

Intercellular interplay between Sirt1 signalling and cell metabolism in immune cell biology

Sirtuins are evolutionarily conserved class III histone deacetylases that have been the focus of intense scrutiny and interest since the discovery of Sir2 as a yeast longevity factor. Early reports demonstrated an important role of Sirt1 in aging and metabolism, but its critical regulatory role in the immune system has only been unveiled in recent years. In this review we discuss the latest advances in understanding the regulatory role of Sirt1 in immune responses as well as how Sirt1 translates metabolic cues to immune signals, which would bring new insights into both pathogenesis and potential therapeutic strategies of a variety of immune-related diseases, such as cancer, microbial infection, autoimmune diseases and transplantation.