The complement anaphylatoxin C5a receptor contributes to obese adipose tissue inflammation and insulin resistance

The potential application of complement inhibitors-loaded nanosystem for autoimmune diseases via regulation immune balance

The complement is an important arm of the innate immune system, once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammation. Recent studies have shown that over-activated complement is the main proinflammatory system of autoimmune diseases (ADs). In addition, activated complements interact with autoantibodies, immune cells exacerbate inflammation, further worsening ADs. With the increasing threat of ADs to human health, complement-based immunotherapy has attracted wide attention. Nevertheless, efficient and targeted delivery of complement inhibitors remains a significant challenge owing to their inherent poor targeting, degradability, and low bioavailability. Nanosystems offer innovative solutions to surmount these obstacles and amplify the potency of complement inhibitors. This prime aim to present the current knowledge of complement in ADs, analyse the function of complement in the pathogenesis and treatment of ADs, we underscore the current situation of nanosystems assisting complement inhibitors in the treatment of ADs. Considering technological, physiological, and clinical validation challenges, we critically appraise the challenges for successfully translating the findings of preclinical studies of these nanosystem assisted-complement inhibitors into the clinic, and future perspectives were also summarised. (The graphical abstract is by BioRender.).

The Past and Future of Inflammation as a Target to Cancer Prevention

Inflammation is an essential defense mechanism in which innate immune cells are coordinately activated on encounter of harmful stimuli, including pathogens, tissue injury, and toxic compounds and metabolites to neutralize and eliminate the instigator and initiate healing and regeneration. Properly terminated inflammation is vital to health, but uncontrolled runaway inflammation that becomes chronic begets a variety of inflammatory and metabolic diseases and increases cancer risk. Making damaged tissues behave as "wounds that do not heal" and sustaining the production of growth factors whose physiologic function is tissue healing, chronic inflammation accelerates cancer emergence from premalignant lesions. In 1863, Rudolf Virchow, a leading German pathologist, suggested a possible association between inflammation and tumor formation, but it took another 140 years to fully elucidate and appreciate the tumorigenic role of inflammation. Key findings outlined molecular events in the inflammatory cascade that promote cancer onset and progression and enabled a better appreciation of when and where inflammation should be inhibited. These efforts triggered ongoing research work to discover and develop inflammation-reducing chemopreventive strategies for decreasing cancer risk and incidence.

From complement to complosome in non-alcoholic fatty liver disease: When location matters

Non-alcoholic fatty liver disease (NAFLD) is a growing public health threat and becoming the leading cause of liver transplantation. Nevertheless, no approved specific treatment is currently available for NAFLD. The pathogenesis of NAFLD is multifaceted and not yet fully understood. Accumulating evidence suggests a significant role of the complement system in the development and progression of NAFLD. Here, we provide an overview of the complement system, incorporating the novel concept of complosome, and summarise the up-to-date evidence elucidating the association between complement dysregulation and the pathogenesis of NAFLD. In this process, the extracellular complement system is activated through various pathways, thereby directly contributing to, or working together with other immune cells in the disease development and progression. We also introduce the complosome and assess the evidence that implicates its potential influence in NAFLD through its direct impact on hepatocytes or non-parenchymal liver cells. Additionally, we expound upon how complement system and the complosome may exert their effects in relation with hepatic zonation in NAFLD. Furthermore, we discuss the potential therapeutic implications of targeting the complement system, extracellularly and intracellularly, for NAFLD treatment. Finally, we present future perspectives towards a better understanding of the complement system's contribution to NAFLD.

The C5aR1 complement receptor: A novel immunomodulator of insulin action in skeletal muscle

The complement system constitutes an integral component of the innate immune system and plays a critical role in adaptive immunity. Activation of this system engenders the production of complement peptide fragments, including C5a, which engage G-protein coupled receptors predominantly expressed in immune-associated cells, such as neutrophils, initiating pro-inflammatory responses. Intriguingly, our investigation has unveiled the presence of C5a receptor 1 (C5aR1) expression within skeletal muscle, a key metabolic tissue and primary target of insulin. Herein, we demonstrate that C5aR1 activation by C5a in differentiated human skeletal muscle cells elicits acute suppression of insulin signalling. This suppression manifests as impaired insulin-dependent association between IRS1 and the p85 subunit of PI3-kinase, a 50% reduction in Akt phosphorylation, and a 60% decline in insulin-stimulated glucose uptake. This impairment in insulin signalling is associated with a three-fold elevation in intramyocellular diacylglycerol (DAG) levels and a two-fold increase in cytosolic calcium content, which promote PKC-mediated IRS1 inhibition via enhanced phosphorylation at IRS1 Ser1101. Significantly, our findings demonstrate that structurally diverse C5aR1 antagonists, along with genetic deletion or stable silencing of C5aR1 by 80% using short-hairpin RNA, effectively attenuate repression of insulin signalling by C5a in LHCN-M2 human skeletal myotubes. These results underscore the potential of heightened C5aR1 activation, characteristic of obesity and chronic inflammatory conditions, to detrimentally impact insulin function within skeletal muscle cells. Additionally, the study suggests that agents targeting the C5a-C5aR axis, originally devised for mitigating complement-dependent inflammatory conditions, may offer therapeutic avenues to ameliorate immune-driven insulin resistance in key peripheral metabolic tissues, including skeletal muscle.

Serum mannan-binding lectin-associated serine proteases in early pregnancy for gestational diabetes in Chinese pregnant women

Aims

This study aimed to explore associations of mannan-binding lectin-associated serine protease (MASP) levels in early pregnancy with gestational diabetes mellitus (GDM). We also examined interactions of MASPs and deoxycholic acid (DCA)/glycoursodeoxycholic acid (GUDCA) for the GDM risk and whether the interactive effects if any on the GDM risk were mediated via lysophosphatidylcholine (LPC) 18:0.

Materials and methods

A 1:1 case-control study (n = 414) nested in a prospective cohort of pregnant women was conducted in Tianjin, China. Binary conditional logistic regressions were performed to examine associations of MASPs with the GDM risk. Additive interaction measures were used to examine interactions between MASPs and DCA/GUDCA for the GDM risk. Mediation analyses and Sobel tests were used to examine mediation effects of LPC18:0 between the copresence of MASPs and DCA/GUDCA on the GDM risk.

Results

High MASP-2 was independently associated with GDM [odds ratio (OR): 2.62, 95% confidence interval (CI): 1.44-4.77], while the effect of high MASP-1 on GDM was attributable to high MASP-2 (P for Sobel test: 0.003). Low DCA markedly increased the OR of high MASP-2 alone from 2.53 (1.10-5.85) up to 10.6 (4.22-26.4), with a significant additive interaction. In addition, high LPC18:0 played a significant mediating role in the links from low DCA to GDM and from the copresence of high MASP-2 and low DCA to GDM (P for Sobel test <0.001) but not in the link from high MASP-2 to GDM.

Conclusions

High MASP-1 and MASP-2 in early pregnancy were associated with GDM in Chinese pregnant women. MASP-2 amplifies the risk of low DCA for GDM, which is mediated via LPC18:0.

Clostridium butyricum Strain CCFM1299 Reduces Obesity via Increasing Energy Expenditure and Modulating Host Bile Acid Metabolism

Clostridium butyricum is a butyrate-producing microorganism which has beneficial effects on various diseases, including obesity. In our previous study, the anti-obesity Clostridium butyricum strain CCFM1299 (C20_1_1) was selected, but its anti-obesity mechanism was not clarified. Herein, CCFM1299 was orally administrated to high-fat-diet-treated C57BL/6J mice for 12 weeks to uncover the way the strain alleviates obesity. The results indicated that CCFM1299 alleviated obesity through increasing the energy expenditure and increasing the expression of genes related to thermogenesis in brown adipose tissue (BAT). Moreover, strain CCFM1299 could also affect the expression of immune-related genes in epididymal white adipose tissue (eWAT). This immunomodulatory effect might be achieved through its influence on the complement system, as the expression of the complement factor D (CFD) gene decreased significantly. From the view of metabolites, CCFM1299 administration increased the levels of ursodeoxycholic acid (UDCA) in feces and taurohyodeoxycholic acid (THDCA) in serum. Together, the anti-obesity potential of CCFM1299 might be attributed to the increase in energy consumption, the regulation of immune-related gene expression in eWAT, and the alteration of bile acid metabolism in the host. These provided new insights into the potential application of anti-obesity microbial preparations and postbiotics.

Obesity and prostate cancer - microenvironmental roles of adipose tissue

Obesity is known to have important roles in driving prostate cancer aggressiveness and increased mortality. Multiple mechanisms have been postulated for these clinical observations, including effects of diet and lifestyle, systemic changes in energy balance and hormonal regulation and activation of signalling by growth factors and cytokines and other components of the immune system. Over the past decade, research on obesity has shifted towards investigating the role of peri-prostatic white adipose tissue as an important source of locally produced factors that stimulate prostate cancer progression. Cells that comprise white adipose tissue, the adipocytes and their progenitor adipose stromal cells (ASCs), which proliferate to accommodate white adipose tissue expansion in obesity, have been identified as important drivers of obesity-associated cancer progression. Accumulating evidence suggests that adipocytes are a source of lipids that are used by adjacent prostate cancer cells. However, results of preclinical studies indicate that ASCs promote tumour growth by remodelling extracellular matrix and supporting neovascularization, contributing to the recruitment of immunosuppressive cells, and inducing epithelial-mesenchymal transition through paracrine signalling. Because epithelial-mesenchymal transition is associated with cancer chemotherapy resistance and metastasis, ASCs are considered to be potential targets of therapies that could be developed to suppress cancer aggressiveness in patients with obesity.

Deletion of complement factor 5 amplifies glucose intolerance in obese male but not female mice

Complement factor 5 of the innate immune system generates C5a and C5b ligands, which initiate inflammatory and cell lysis events, respectively. C5 activation has been linked with obesity-associated metabolic disorders; however, whether it has a causative role is unclear. We generated a C5 null (C5-/-) mouse using CRISPR-Cas9 gene editing to determine whether loss of C5 improves obesity-linked metabolic dysfunction. Generation of a new mouse model was prompted in part by the observation of off-target gene mutations in commercially available C5-/- lines. Male and female wild-type (WT), heterozygous (Het), and C5-/- mice were fed low-fat diet (LFD) or high-fat diet (HFD) for 22 wk. Body weight gain did not differ between genotypes on LFD or HFD. In lean animals, male C5-/- mice had similar glucose tolerance compared with WT controls; however, in obese conditions, glucose tolerance was worsened in C5-/- compared with controls. In contrast, female mice did not exhibit differences in glucose tolerance between genotypes under either dietary paradigm. Fasting insulin was not different between genotypes, whereas diet-induced obese male C5-/- mice had lower fed insulin concentrations compared with WT controls. No differences in adipose tissue inflammation or adipocyte size were identified between groups. Similarly, susceptibility to fatty liver and hepatic inflammation was similar between WT and C5-/- mice. However, the systemic cytokine response to acute endotoxin exposure was decreased in C5-/- mice. Together, these data suggest that loss of C5 worsens glucose tolerance in obese male but not female mice. Additional work is required to pinpoint the mechanisms by which loss of C5 amplifies glucose intolerance in obesity.NEW & NOTEWORTHY We generated a new mouse model of complement factor 5 deficiency. This work was prompted by a need for improved transgenic mouse lines of C5, due to off-target gene mutations. We find that loss of C5 worsens glucose tolerance in a sex-dependent manner. Though the mechanisms evoking glucose intolerance are not clear, we are confident this model will be useful in interrogating complement activation in obesity-associated diseases.

Effects of T cell leptin signaling on systemic glucose tolerance and T cell responses in obesity

BACKGROUND/OBJECTIVES

Leptin is an adipokine secreted in proportion to adipocyte mass and is therefore increased in obesity. Leptin signaling has been shown to directly promote inflammatory T helper 1 (Th1) and T helper 17 (Th17) cell number and function. Since T cells have a critical role in driving inflammation and systemic glucose intolerance in obesity, we sought to determine the role of leptin signaling in this context.

METHODS

Male and female T cell-specific leptin receptor knockout mice and littermate controls were placed on low-fat diet or high-fat diet to induce obesity for 18 weeks. Weight gain, serum glucose levels, systemic glucose tolerance, T cell metabolism, and T cell differentiation and cytokine production were examined.

RESULTS

In both male and female mice, T cell-specific leptin receptor deficiency did not reverse impaired glucose tolerance in obesity, although it did prevent impaired fasting glucose levels in obese mice compared to littermate controls, in a sex dependent manner. Despite these minimal effects on systemic metabolism, T cell-specific leptin signaling was required for changes in T cell metabolism, differentiation, and cytokine production observed in mice fed high-fat diet compared to low-fat diet. Specifically, we observed increased T cell oxidative metabolism, increased CD4+ T cell IFN-γ expression, and increased proportion of T regulatory (Treg) cells in control mice fed high-fat diet compared to low-fat diet, which were not observed in the leptin receptor conditional knockout mice, suggesting that leptin receptor signaling is required for some of the inflammatory changes observed in T cells in obesity.

CONCLUSIONS

T cell-specific deficiency of leptin signaling alters T cell metabolism and function in obesity but has minimal effects on obesity-associated systemic metabolism. These results suggest a redundancy in cytokine receptor signaling pathways in response to inflammatory signals in obesity.

Therapeutic Potential of Targeting Complement C5a Receptors in Diabetic Kidney Disease

Diabetic kidney disease (DKD) affects 30-40% of patients with diabetes and is currently the leading cause of end-stage renal disease (ESRD). The activation of the complement cascade, a highly conserved element of the innate immune system, has been implicated in the pathogenesis of diabetes and its complications. The potent anaphylatoxin C5a is a critical effector of complement-mediated inflammation. Excessive activation of the C5a-signalling axis promotes a potent inflammatory environment and is associated with mitochondrial dysfunction, inflammasome activation, and the production of reactive oxygen species. Conventional renoprotective agents used in the treatment of diabetes do not target the complement system. Mounting preclinical evidence indicates that inhibition of the complement system may prove protective in DKD by reducing inflammation and fibrosis. Targeting the C5a-receptor signaling axis is of particular interest, as inhibition at this level attenuates inflammation while preserving the critical immunological defense functions of the complement system. In this review, the important role of the C5a/C5a-receptor axis in the pathogenesis of diabetes and kidney injuries will be discussed, and an overview of the status and mechanisms of action of current complement therapeutics in development will be provided.

Potential causal role of synovial complement system activation in the development of post-traumatic osteoarthritis after anterior cruciate ligament injury or meniscus tear

Anterior cruciate ligament (ACL) injury and meniscal tear (MT) are major causal factors for developing post-traumatic osteoarthritis (PTOA), but the biological mechanism(s) are uncertain. After these structural damages, the synovium could be affected by complement activation that normally occurs in response to tissue injury. We explored the presence of complement proteins, activation products, and immune cells, in discarded surgical synovial tissue (DSST) collected during arthroscopic ACL reconstructive surgery, MT-related meniscectomy and from patients with OA. Multiplexed immunohistochemistry (MIHC) was used to determine the presence of complement proteins, receptors and immune cells from ACL, MT, OA synovial tissue vs. uninjured controls. Examination of synovium from uninjured control tissues did not reveal the presence of complement or immune cells. However, DSST from patients undergoing ACL and MT repair demonstrated increases in both features. In ACL DSST, a significantly higher percentage of C4d+, CFH+, CFHR4+ and C5b-9+ synovial cells were present compared with MT DSST, but no major differences were seen between ACL and OA DSST. Increased cells expressing C3aR1 and C5aR1, and a significant increase in mast cells and macrophages, were found in ACL as compared to MT synovium. Conversely, the percentage of monocytes was increased in the MT synovium. Our data demonstrate that complement is activated in the synovium and is associated with immune cell infiltration, with a more pronounced effect following ACL as compared to MT injury. Complement activation, associated with an increase in mast cells and macrophages after ACL injury and/or MT, may contribute to the development of PTOA.

Loss of C3a and C5a receptors promotes adipocyte browning and attenuates diet-induced obesity via activating inosine/A2aR pathway

Complement activation is thought to underline the pathologic progression of obesity-related metabolic disorders; however, its role in adaptive thermogenesis has scarcely been explored. Here, we identify complement C3a receptor (C3aR) and C5a receptor (C5aR) as critical switches to control adipocyte browning and energy balance in male mice. Loss of C3aR and C5aR in combination, more than individually, increases cold-induced adipocyte browning and attenuates diet-induced obesity in male mice. Mechanistically, loss of C3aR and C5aR increases regulatory T cell (Treg) accumulation in the subcutaneous white adipose tissue during cold exposure or high-fat diet. Activated Tregs produce adenosine, which is converted to inosine by adipocyte-derived adenosine deaminases. Inosine promotes adipocyte browning in a manner dependent on activating adenosine A2a receptor. These data reveal a regulatory mechanism of complement in controlling adaptive thermogenesis and suggest that targeting the C3aR/C5aR pathways may represent a therapeutic strategy in treating obesity-related metabolic diseases.

Supplementing Diets with Agriophyllum squarrosum Reduced Blood Lipids, Enhanced Immunity and Anti-Inflammatory Capacities, and Mediated Lipid Metabolism in Tan Lambs

Agriophyllum squarrosum (sand rice), a widespread desert plant, possesses anti-hyperglycemic and anti-inflammatory properties, and has been used in traditional Chinese medicine for many years. However, its effects on ruminants are unknown. To fill this gap, we examined the effects of A. squarrosum on the immune and anti-inflammatory responses of lambs. A total of 23, 6-month-old Tan ewe-lambs (27.6 ± 0.47 kg) were divided into four groups and offered a basic diet (C—control), or a diet that contained 10%, 20%, or 30% A. squarrosum, on a dry matter basis, for 128 days. Serum concentrations of total cholesterol were lower (p = 0.004) in the 30% supplemented lambs than controls, while concentrations of high-density lipoprotein cholesterol were lower (p = 0.006) in the 10% and 20%, but not in 30% supplemented lambs than controls. Serum-cortisol concentrations were lower (p = 0.012) in the 30% supplemented lambs and free fatty acid concentrations were higher in the 10% and 20% supplemented lambs than in control lambs (p < 0.001). Supplementation with A. squarrosum decreased (p < 0.05) the area of adipocytes in subcutaneous adipose tissue, but there was no difference between the 20% and 30% diets. Conversely, the area in visceral adipose tissue (VAT) increased (p < 0.05), especially for the 10% and 20% supplemented diets. Supplementation with A. squarrosum also enriched immune and anti-inflammatory related and lipid and glucose-metabolic pathways and associated differentially expressed gene expressions in adipose tissue. A total of 10 differential triacylglycerol, 34 differential phosphatidylcholines and seven differential phosphatidylethanolamines decreased in the diet with 30% supplementation, when compared to the other diets. Finally, adipocyte-differentiation genes, and immune and inflammatory response-related gene expression levels decreased in lamb adipocytes cultured with an aqueous A. squarrosum extract. In conclusion, supplementing lamb diets with A. squarrosum reduced blood lipids, enhanced immunity and anti-inflammatory capacities, and mediated lipid metabolism in adipose tissue and adipocytes of Tan lambs. A level of approximately 10% is recommended, but further research is required to determine the precise optimal level.

The role of complement in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become a leading cause of chronic liver diseases globally. NAFLD includes a range of hepatic manifestations, starting with liver steatosis and potentially evolving towards nonalcoholic steatohepatitis, cirrhosis or even hepatocellular carcinoma. Although the pathogenesis of NAFLD is incompletely understood, insulin resistance and lipid metabolism disorder are implicated. The complement system is an essential part of the immune system, but it is also involved in lipid metabolism. In particular, activation of the alternative complement pathway and the production of complement activation products such as C3a, C3adesArg (acylation stimulating protein or ASP) and C5a, are strongly associated with insulin resistance, lipid metabolism disorder, and hepatic inflammation. In this review, we briefly summarize research on the role of the complement system in NAFLD, aiming to provide a basis for the development of novel therapeutic strategies for NAFLD.

Differential expression of plasma exosomal microRNA in severe acute pancreatitis

The incidence rate of acute pancreatitis is increasing, and severe acute pancreatitis (SAP) is associated with a high mortality rate, which may be reduced by a deeper understanding of its pathogenesis. In addition, an early determination of the severity of acute pancreatitis remains challenging. The aim of this study was to match potential biomarkers for early identification and monitoring of acute pancreatitis and to shed light on the underlying pathogenic mechanisms of SAP. The expression levels of plasma exosomal microRNA (miRNA) in patients with pancreatitis have been associated with the disease. Thus, this study compared the expression levels of exosomal miRNA in plasma collected from four patients with SAP and from four healthy participants. Analyses of the miRNA expression profiles indicated that three previously unreported miRNAs were differentially expressed in the patient group: Novel1, which was downregulated, and Novel2 and Novel3, which were upregulated. The miRNA target genes for those novel miRNAs were predicted using Metascape. Of these miRNA target genes, those that were also differentially expressed at different time points after disease induction in a mouse model of acute pancreatitis were determined. The gene for complement component 3 (C3), a target gene of Novel3, was the only gene matched in both the patient group and the mouse model. C3 appeared at most of the time points assessed after induction of acute pancreatitis in mice. These findings are foundational evidence that C3 warrants further study as an early biomarker of SAP, for investigating underlying pathogenic mechanisms of SAP, and as a therapeutic target for ameliorating the occurrence or development of SAP.

Apolipoprotein C3 and circulating mediators of preadipocyte proliferation in states of lipodystrophy

Adipogenesis is a complex process controlled by intrinsic and extrinsic factors that regulate preadipocyte proliferation, adipogenic capacity and maturation of metabolic function. Here we show that insulin and IGF-1 receptors are essential for mature adipocyte survival and that deletion of both IR and IGF1R specifically in fat using a tamoxifen inducible-AdipoQ-Cre (Ai-DKO) leads to rapid and severe loss of adipocytes in all depots, associated with a metabolic syndrome characterized by hypertriglyceridemia, hyperglycemia, hyperinsulinemia, fatty liver, and pancreatic beta cell proliferation. In this model, this pathological phenotype reverses over a few weeks, in large part, due to preadipocyte proliferation and adipose tissue regeneration. Incubation of preadipocytes with serum from the Ai-DKO mice in vitro stimulates cell proliferation, and this effect can be mimicked by conditioned media from liver slices of Ai-DKO mice, but not by media of cultured Ai-DKO adipocytes, indicating a hepatic origin of the growth factor. Proteomic analysis of serum reveals apolipoprotein C3 (APOC3), a protein secreted by liver, as one of the most upregulated proteins in the Ai-DKO mice. In vitro, purified and delipidated APOC3 stimulates preadipocyte proliferation, however, knockdown of hepatic APOC3 in vivo in Ai-DKO mice is not sufficient to block adipose regeneration. Thus, lipodystrophy is associated with presence of increased preadipocyte-stimulating growth factors in serum. Our study indicates that APOC3 is one contributing factor to preadipocyte proliferation, however, other still-unidentified circulating growth factors are also likely present in Ai-DKO mice. Identification of these factors may provide a new approach to regulation of adipose mass in health and disease.

Macrophages, Low-Grade Inflammation, Insulin Resistance and Hyperinsulinemia: A Mutual Ambiguous Relationship in the Development of Metabolic Diseases

Metabolic derangement with poor glycemic control accompanying overweight and obesity is associated with chronic low-grade inflammation and hyperinsulinemia. Macrophages, which present a very heterogeneous population of cells, play a key role in the maintenance of normal tissue homeostasis, but functional alterations in the resident macrophage pool as well as newly recruited monocyte-derived macrophages are important drivers in the development of low-grade inflammation. While metabolic dysfunction, insulin resistance and tissue damage may trigger or advance pro-inflammatory responses in macrophages, the inflammation itself contributes to the development of insulin resistance and the resulting hyperinsulinemia. Macrophages express insulin receptors whose downstream signaling networks share a number of knots with the signaling pathways of pattern recognition and cytokine receptors, which shape macrophage polarity. The shared knots allow insulin to enhance or attenuate both pro-inflammatory and anti-inflammatory macrophage responses. This supposedly physiological function may be impaired by hyperinsulinemia or insulin resistance in macrophages. This review discusses the mutual ambiguous relationship of low-grade inflammation, insulin resistance, hyperinsulinemia and the insulin-dependent modulation of macrophage activity with a focus on adipose tissue and liver.

The Complement System in Metabolic-Associated Kidney Diseases

Metabolic syndrome (MS) is a group of clinical abnormalities characterized by central or abdominal obesity, hypertension, hyperuricemia, and metabolic disorders of glucose or lipid. Currently, the prevalence of MS is estimated about 25% in general population and is progressively increasing, which has become a challenging public health burden. Long-term metabolic disorders can activate the immune system and trigger a low-grade chronic inflammation named “metaflammation.” As an important organ involved in metabolism, the kidney is inevitably attacked by immunity disequilibrium and “metaflammation.” Recently, accumulating studies have suggested that the complement system, the most important and fundamental component of innate immune responses, is actively involved in the development of metabolic kidney diseases. In this review, we updated and summarized the different pathways through which the complement system is activated in a series of metabolic disturbances and the mechanisms on how complement mediate immune cell activation and infiltration, renal parenchymal cell damage, and the deterioration of renal function provide potential new biomarkers and therapeutic options for metabolic kidney diseases.

Synergism between obesity and HFpEF on neutrophils phenotype and its regulation by adipose tissue-molecules and SGLT2i dapagliflozin

The adiposity invokes innate immune activity, coronary microvascular dysfunction and consequently heart failure preserved ejection fraction (HFpEF). Our aim was to study the neutrophils profile on obesity and cardiovascular disease and its regulation by adipose tissue-secretome and dapagliflozin. We have isolated neutrophils from patients undergoing open heart surgery (19 women and 51 men). Its migration activity was performed with culture-transwell, transcriptional studies of proteolytic enzymes, adhesion molecules or receptors were analysed by real-time PCR and proteomics (from 20 patients) analysis by TripleTOF mass spectrometer. Differentiated HL-60 (dHL-60) was used as a preclinical model on microfluidic for endothelial cells attaching assays and genes regulation with epicardial and subcutaneous fat secretomes from patients (3 women and 9 men) or dapagliflozin 1-10 μM treatments. The transcriptional and proteomics studies have determined higher levels of adhesion molecules in neutrophils from patients with obesity. The adhesion molecule CD11b levels were higher in those patients with the combined obesity and HFpEF factors (1.70 ± 0.06 a.u. without obesity, 1.72 ± 0.04 a.u. obesity or HFpEF without obesity and 1.79 ± 0.08 a.u. obesity and HFpEF; p < .01). While fat-secretome induces its upregulation, dapagliflozin can modulated it. Because CD11b upregulation is associated with higher neutrophils migration and adhesion into endothelial cells, dapagliflozin might modulate this mechanism on patients with obesity and HFpEF.

Complement Inhibition Alleviates Cholestatic Liver Injury Through Mediating Macrophage Infiltration and Function in Mice

Background and Aims

Cholestatic liver injury (CLI), which is associated with inflammatory reactions and oxidative stress, is a serious risk factor for postoperative complications. Complement system is involved in a wide range of liver disorders, including cholestasis. The present study assessed the role of complement in CLI and the therapeutic effect of the site-targeted complement inhibitor CR2-Crry in CLI.

Methods

Wild-type and complement gene deficient mice underwent common bile duct ligation (BDL) to induce CLI or a sham operation, followed by treatment with CR2-Crry or GdCl3. The roles of complement in CLI and the potential therapeutic effects of CR2-Crry were investigated by biochemical analysis, flow cytometry, immunohistochemistry, ELISA, and quantitative RT-PCR.

Results

C3 deficiency and CR2-Crry significantly reduced liver injuries in mice with CLI, and also markedly decreasing the numbers of neutrophils and macrophages in the liver. C3 deficiency and CR2-Crry also significantly reduced neutrophil expression of Mac-1 and liver expression of VCAM-1. More importantly, C3 deficiency and CR2-Crry significantly inhibited M1 macrophage polarization in these mice. Intravenous injection of GdCl3 inhibited macrophage infiltration and activation in the liver. However, the liver injury increased significantly. BDL significantly increased the level of lipopolysaccharide (LPS) in portal blood, but not in peripheral blood. GdCl3 significantly increased LPS in peripheral blood, suggesting that macrophages clear portal blood LPS. Oral administration of ampicillin to in GdCl3 treated mice reduced LPS levels in portal blood and alleviated liver damage. In contrast, intraperitoneal injection LPS increased portal blood LPS and reversed the protective effect of ampicillin. Interestingly, C3 deficiency did not affect the clearance of LPS.

Conclusions

Complement is involved in CLI, perhaps mediating the infiltration and activation of neutrophils and macrophage M1 polarization in the liver. C3 deficiency and CR2-Crry significantly alleviated CLI. Inhibition of complement could preserve the protective function of macrophages in clearing LPS, suggesting that complement inhibition could be useful in treating CLI.

Tissue differences in the exosomal/small extracellular vesicle proteome and their potential as indicators of altered tissue metabolism

Exosomes/small extracellular vesicles (sEVs) can serve as multifactorial mediators of cell-to-cell communication through their miRNA and protein cargo. Quantitative proteomic analysis of five cell lines representing metabolically important tissues reveals that each cell type has a unique sEV proteome. While classical sEV markers such as CD9/CD63/CD81 vary markedly in abundance, we identify six sEV markers (ENO1, GPI, HSPA5, YWHAB, CSF1R, and CNTN1) that are similarly abundant in sEVs of all cell types. In addition, each cell type has specific sEV markers. Using fat-specific Dicer-knockout mice with decreased white adipose tissue and increased brown adipose tissue, we show that these cell-type-specific markers can predict the changing origin of the serum sEVs. These results provide a valuable resource for understanding the sEV proteome of the cells and tissues important in metabolic homeostasis, identify unique sEV markers, and demonstrate how these markers can help in predicting the tissue of origin of serum sEVs.

By performing comparative proteomics, Garcia-Martin et al. identify markers common to exosomes/sEVs from multiple cell types, as well as markers unique to each cell type. Using a lipodystrophy mouse model, they demonstrate the use of this sEV proteome dataset to predict the tissue of origin of circulating exosomes/sEVs in vivo.

Innate-Immunity Genes in Obesity

The main functions of adipose tissue are thought to be storage and mobilization of the body’s energy reserves, active and passive thermoregulation, participation in the spatial organization of internal organs, protection of the body from lipotoxicity, and ectopic lipid deposition. After the discovery of adipokines, the endocrine function was added to the above list, and after the identification of crosstalk between adipocytes and immune cells, an immune function was suggested. Nonetheless, it turned out that the mechanisms underlying mutual regulatory relations of adipocytes, preadipocytes, immune cells, and their microenvironment are complex and redundant at many levels. One possible way to elucidate the picture of adipose-tissue regulation is to determine genetic variants correlating with obesity. In this review, we examine various aspects of adipose-tissue involvement in innate immune responses as well as variants of immune-response genes associated with obesity.

Role of C5a and C5aR in doxorubicin-induced cardiomyocyte senescence

Doxorubicin (DOX) is an efficacious antineoplastic drug; however, its use is limited due to its cardiotoxicity. Cardiomyocyte senescence is considered to be a key factor in the development of DOX-related cardiomyopathy. Complement component 5a (C5a) and the C5a receptor (C5aR) have been reported to play a key role in the process of cellular senescence. However, to the best of our knowledge, the exact role of C5a and C5aR in cellular senescence in the heart remains largely unknown. Reverse transcription-quantitative (RT-q)PCR and western blot assays were used to analyze the expression levels of C5a and C5aR in H9c2 embryonic rat cardiomyocytes and AC16 human cardiomyocyte-like cells. The cells were treated with DOX and a C5aR antagonist (C5aRA). The expression of TNF-α and IFN-γ was determined using ELISA and western blotting. The levels of reactive oxygen species (ROS) were also measured using ELISA. Cellular senescence was determined using senescence-associated β-galactosidase (SA-β-gal) staining and by analyzing the protein expression levels of p53, p16, p21 and insulin-like growth factor-binding protein 3 (IGFBP3). The expression levels of C5a and C5aR were found to be upregulated during the DOX-induced senescence of H9c2 and AC16 cardiomyocytes. Treatment with C5aRA downregulated TNF-α and IFN-γ expression, in addition to ROS levels. Furthermore, C5aRA prevented DOX-induced cellular senescence and decreased the levels of positive SA-β-gal staining in H9c2 and AC16 cardiomyocytes, in addition to downregulating the expression levels of p53, p16, p21 and IGFBP3. C5aRA also increased the telomere length and telomerase activity in H9c2 and AC16 cardiomyocytes following DOX stimulation. In conclusion, the findings of the present study indicated that C5a and C5aR may play a key role in cardiomyocyte senescence, and treatment with C5aRA may be an effective method for preventing DOX-induced cardiomyocyte aging.

Complement in metabolic disease: metaflammation and a two-edged sword

We are currently experiencing an enduring global epidemic of obesity and diabetes. It is now understood that chronic low-grade tissue inflammation plays an important role in metabolic disease, brought upon by increased uptake of a so-called Western diet, and a more sedentary lifestyle. Many evolutionarily conserved links exist between metabolism and the immune system, and an imbalance in this system induced by chronic over-nutrition has been termed 'metaflammation'. The complement system is an important and evolutionarily ancient part of innate immunity, but recent work has revealed that complement not only is involved in the recognition of pathogens and induction of inflammation, but also plays important roles in cellular and tissue homeostasis. Complement can therefore contribute both positively and negatively to metabolic control, depending on the nature and anatomical site of its activity. This review will therefore focus on the interactions of complement with mechanisms and tissues relevant for metabolic control, obesity and diabetes.

Hyperoside attenuates non-alcoholic fatty liver disease through targeting Nr4A1 in macrophages

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance and a systemic pro-inflammatory response. To date, no medications for NAFLD have been approved by relevant governmental agencies. Emerging evidence indicates that innate immune mechanisms are pivotal drivers of inflammation and other pathological manifestations observed in NAFLD. Hyperoside, a flavonoid compound mainly found in medicinal plants, has many biological effects, but the role of hyperoside in the physiological process of NAFLD is poorly defined. This study demonstrated that hyperoside exerts protective effects against high-fat diet (HFD)-induced NAFLD and regulates macrophage polarization in an Nr4A1-dependent manner. After 16 weeks on a HFD, hepatic steatosis, insulin resistance, and inflammatory responses were significantly ameliorated in hyperoside-treated HFD-fed wild-type mice, and hyperoside facilitated the polarization of macrophages from the pro-inflammatory M1 to the anti-inflammatory M2 subtype. Nr4A1 was found to be upregulated in hyperoside-treated HFD-fed mice, and hyperoside did not improve HFD-induced NAFLD or regulate macrophage polarization in Nr4A1-deficient mice. In conclusion, hyperoside may have therapeutic potential in preventing the pathological progression of NAFLD.

We Should Do More to Offer Evidence-Based Treatment for an Important Modifiable Risk Factor for COVID-19: Obesity

Observational studies, from multiple countries, repeatedly demonstrate an association between obesity and severe COVID-19, which is defined as need for hospitalization, intensive care unit admission, invasive mechanical ventilation (IMV) or death. Meta-analysis of studies from China, USA, and France show odds ratio (OR) of 2.31 (95% CI 1.3-4.1) for obesity and severe COVID-19. Other studies show OR of 12.1 (95% CI 3.25-45.1) for mortality and OR of 7.36 (95% CI 1.63-33.14) for need for IMV for patients with body mass index (BMI) ≥ 35 kg/m². Obesity is the only modifiable risk factor that is not routinely treated but treatment can lead to improvement in visceral adiposity, insulin sensitivity, and mortality risk. Increasing the awareness of the association between obesity and COVID-19 risk in the general population and medical community may serve as the impetus to make obesity identification and management a higher priority.

Immunohistochemical identification of complement peptide C5a receptor 1 (C5aR1) in non-neoplastic and neoplastic human tissues

The complement component C5a and its receptor C5aR1 are involved in the development of numerous inflammatory diseases. In addition to immune cells, C5aR1 is expressed in neoplastic cells of multiple tumour entities, where C5aR1 is associated with a higher proliferation rate, advanced tumour stage, and poor patient outcomes. The aim of the present study was to obtain a broad expression profile of C5aR1 in human non-neoplastic and neoplastic tissues, especially in tumour entities not investigated in this respect so far. For this purpose, we generated a novel polyclonal rabbit antibody, {5227}, against the carboxy-terminal tail of C5aR1. The antibody was initially characterised in Western blot analyses and immunocytochemistry using transfected human embryonic kidney (HEK) 293 cells. It was then applied to a large series of formalin-fixed, paraffin-embedded non-neoplastic and neoplastic human tissue samples. C5aR1 was strongly expressed by different types of immune cells in the majority of tissue samples investigated. C5aR1 was also present in alveolar macrophages, bronchial, gut, and bile duct epithelia, Kupffer cells, occasionally in hepatocytes, proximal renal tubule cells, placental syncytiotrophoblasts, and distinct stem cell populations of bone marrow. C5aR1 was also highly expressed in the vast majority of the 32 tumour entities investigated, where a hitherto unappreciated high prevalence of the receptor was detected in thyroid carcinomas, small-cell lung cancer, gastrointestinal stromal tumours, and endometrial carcinomas. In addition to confirming published findings, we found noticeable C5aR1 expression in many tumour entities for the first time. Here, it may serve as an interesting target for future therapies.

Hematological reactions in the inhabitants of the Arctic on a polar night and a polar day

PURPOSE

The purpose of this study is to identify the features of hematological reactions in the inhabitants of the Arctic territory of the Kola Peninsula on a polar night and a polar day.

METHODS

The study included determining the hemogram, neutrograms, monocytograms, lymphocytograms, and phagocytic activity neutrophil granulocytes, enzyme immunoassay, flow cytometry.

RESULTS

It was established that during the polar night, there is an increase in the activity of migration of leukocytes from the marginal pool to the circulating pool, an increase in the intensity of phagocytosis by neutrophils, an increase in the concentrations of noradrenaline, cortisol, as well as an increase in hyperergic reactions involving immunoglobulin E and inhibitory processes due to an increase in interleukin-10.

CONCLUSION

A prolonged lack of sunlight causes a decrease in the reserve capacity for regulating homeostasis and forces the body to use proliferative reactions, which is reflected in the increase in stab neutrophils, large lymphocytes in the structure of the lymphocytogram and CD10+ lymphocytes. In winters, the frequency of neutropenia registration also increases to 13% of cases, the deficit of phagocytic activity of neutrophils; lymphopenia is recorded in 20% with T-helper deficiency (37%). A part of the population probably has a relatively high degree of vulnerability to the action of natural environmental factors and is not able to completely restore the initial levels of the effectiveness of adaptation reactions in the summer. So at the end of the polar day in 8% of adults born in the north, neutropenia is recorded and in 21%-lymphopenia.

Transcriptome changes associated with fat deposition in the longissimus thoracis of Korean cattle following castration

The castration of bulls increases the intramuscular fat (IMF) content in skeletal muscle. However, the biological processes of IMF accumulation in skeletal muscle after castration are not completely understood at the molecular level. This study examined the global transcriptomic changes in the longissimus thoracis muscle (LT) of bulls following castration using RNA sequencing (RNA-Seq) and identified new genes or pathways associated with beef quality. Ten bulls and 10 steers castrated at 6 months of age were slaughtered at 26 and 32 months of age respectively. For transcriptome analysis, six LT samples from three bulls and three steers were selected based on age, carcass weight, carcass quantity and beef quality grades. Using RNA-Seq, transcriptomic profiles of the LT were compared between bulls and steers. In all, 640 of the 18,027 genes identified through RNA-Seq were differentially expressed genes (DEGs) between bulls and steers. Pathway analysis of these 640 DEGs showed significant (p < .05) changes in seven Kyoto Encyclopedia of Genes and Genomes pathways, and the most significant terms were complement and coagulation cascade pathways. The transcriptomic expression patterns of 10 genes in the complement and coagulation cascades were validated using all animals through quantitative real-time polymerase chain reaction analysis. In conclusion, transcriptome changes associated with the complement and coagulation cascade pathways provide novel insights into understanding molecular mechanisms responsible for IMF accumulation following castration in beef cattle.

Loss of iRhom2 accelerates fat gain and insulin resistance in diet-induced obesity despite reduced adipose tissue inflammation

BACKGROUND

Low-grade inflammation and metabolic dysregulation are common comorbidities of obesity, both of which are associated with alterations in iRhom2-regulated pro-inflammatory cytokine and epidermal growth factor receptor (EGFR) ligand signaling.

OBJECTIVE

Our objective was to determine the role of iRhom2 in the regulation of low-grade inflammation and metabolic dysregulation in a murine model of diet-induced obesity.

METHODS

Wild type (WT) and iRhom2-deficient mice were fed normal chow (NC) or a high-fat diet (HFD) starting at 5 weeks of age for up to 33 weeks. Body composition, glucose and insulin tolerance, feeding behavior, and indirect calorimetry were measured at defined time points. Adipose tissue cytokine expression and inflammatory lesions known as crown-like structures (CLS) were analyzed at the end-point of the study.

RESULTS

iRhom2-deficient mice show accelerated fat gain on a HFD, accompanied by insulin resistance. Indirect calorimetry did not demonstrate changes in energy expenditure or food intake, but locomotor activity was significantly reduced in HFD iRhom2-deficient mice. Interestingly, CLS, macrophage infiltration, and tumor necrosis factor (TNF) production were decreased in adipose tissue from HFD iRhom2-deficient mice, but circulating cytokines were unchanged. In inguinal and perigonadal fat, the EGFR ligand amphiregulin was markedly induced in HFD controls but completely prevented in iRhom2-deficient mice, suggesting a potentially dominant role of EGFR-dependent mechanisms over TNF in the modulation of insulin sensitivity.

CONCLUSIONS

This study elucidates a novel role for iRhom2 as an immuno-metabolic regulator that affects adipose tissue inflammation independent of insulin resistance.

The potential interplay between energy metabolism and innate complement activation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing motor neuron disease without effective treatment. Although the precise mechanisms leading to ALS are yet to be determined, there is now increasing evidence implicating the defective energy metabolism and components of the innate immune complement system in the onset and progression of its motor phenotypes. This review will survey the mechanisms by which the energy metabolism and the complement system are altered during the disease progression of ALS and how it can contribute to disease. Furthermore, it will also examine how complement activation can modify the energy metabolism in metabolic disorders, in order to highlight how the complement system and energy metabolism may be linked in ALS.

The hepatocyte-specifically expressed lnc-HSER alleviates hepatic fibrosis by inhibiting hepatocyte apoptosis and epithelial-mesenchymal transition

Liver fibrosis leading to cirrhosis is one of the major health burdens worldwide with currently limited therapeutic options available. Long noncoding RNAs (lncRNAs) play important roles in various biological and pathological processes in a cell- or tissue-specific manner. However, there is still an important gap in the understanding of the role of hepatocyte-specific lncRNAs in liver fibrosis. Methods: The expressions of lnc-Hser in human and mice fibrotic livers as well as primary hepatocytes (HCs) of mice developing liver fibrosis were determined by real-time RT-PCR. The roles and mechanisms of lnc-Hser in HCs and liver fibrosis were determined in vitro and in vivo. Results: In this study, we have identified a hepatocyte-specifically expressed lnc-Hser, which was reduced in human and mice fibrotic livers as well as primary HCs of mice developing liver fibrosis. We have shown that silencing lnc-Hser aggravated liver fibrosis both in vitro and in vivo through inducing the epithelial-mesenchymal transition (EMT) and the apoptosis of HCs. In addition, knockdown of lnc-Hser promoted hepatic stellate cells (HSCs) activation through the signals derived from injured HCs. Mechanistically, we have revealed that lnc-Hser inhibited HCs apoptosis via the C5AR1-Hippo-YAP pathway and suppressed HCs EMT via the Notch signaling. Conclusions: Our work has identified a hepatocyte-specific lnc-HSER that regulates liver fibrosis, providing a proof that this molecule is a novel biomarker for damaged HCs and a potential target for anti-fibrotic therapy.

Complement C5a inhibition moderates lipid metabolism and reduces tubulointerstitial fibrosis in diabetic nephropathy

Background

Complement C5 mediates pro-inflammatory responses in many immune-related renal diseases. Given that the C5a level is elevated in diabetes, we investigated whether activation of C5a/C5aR signalling plays a pathogenic role in diabetic nephropathy (DN) and the therapeutic potential of C5a inhibition for renal fibrosis.

Methods

Human renal biopsies from patients with DN and control subjects were used for immunohistochemical staining of complement C5 components. Renal function and tubulointerstitial injury were compared between db/m mice, vehicle-treated mice and C5a inhibitor-treated db/db mice. A cell culture model of tubule epithelial cells (HK-2) was used to demonstrate the effect of C5a on the renal fibrotic pathway.

Results

Increased levels of C5a, but not of its receptor C5aR, were detected in renal tubules from patients with DN. The intensity of C5a staining was positively correlated with the progression of the disease. In db/db mice, administration of a novel C5a inhibitor, NOX-D21, reduced the serum triglyceride level and attenuated the upregulation of diacylglycerolacyltransferase-1 and sterol-regulatory element binding protein-1 expression and lipid accumulation in diabetic kidney. NOX-D21-treated diabetic mice also had reduced serum blood urea nitrogen and creatinine levels with less glomerular and tubulointerstitial damage. Renal transforming growth factor beta 1 (TGF-β1), fibronectin and collagen type I expressions were reduced by NOX-D21. In HK-2 cells, C5a stimulated TGF-β production through the activation of the PI3K/Akt signalling pathway.

Conclusions

Blockade of C5a signalling by NOX-D21 moderates altered lipid metabolism in diabetes and improved tubulointerstitial fibrosis by reduction of lipid accumulation and TGF-β-driven fibrosis in diabetic kidney.

Complement C3 exacerbates renal interstitial fibrosis by facilitating the M1 macrophage phenotype in a mouse model of unilateral ureteral obstruction

The impact of the renal microenvironment on macrophage phenotype determination can contribute to the progression or resolution of renal fibrosis. Although the complement proteins affect macrophage polarization, whether complement component 3 (C3) can induce macrophage polarization and regulate renal interstitial fibrosis remains undetermined. In the present study, we investigated the contribution of C3 on macrophage polarization and renal fibrosis in C3-deficient mice with unilateral ureteral obstruction and bone marrow-derived macrophages. C3-deficient mice exhibited attenuated renal fibrosis and ameliorated peritubular capillary rarefaction. Lack of C3 contributed to M2 macrophage polarization, increased IL-10 and VEGF164, and decreased TNF-α and soluble VEGF receptor 1 expression in the obstructed kidneys at the early stages of unilateral ureteral obstruction. C3a facilitated LPS-induced M1 polarization and inflammatory factor production in bone marrow-derived macrophages in vitro, accompanied by increased ERK, NF-κB, and STAT1 phosphorylation. The ERK-specific inhibitor PD98059 inhibited the phosphorylation of ERK, NF-κB, and STAT1 and attenuated M1 polarization-related inflammatory factor production. Furthermore, the culture supernatant from M1 macrophages and C3a-treated M2 macrophages were more detrimental to angiogenesis compared with M2 macrophage supernatants. Thus, complement C3 exacerbates renal interstitial fibrosis by facilitating macrophage M1 polarization, promoting proinflammatory cytokine expression, and deteriorating peritubular capillary rarefaction in the kidney.

Contribution of Adipose Tissue Inflammation to the Development of Type 2 Diabetes Mellitus

The objective of this comprehensive review is to summarize and discuss the available evidence of how adipose tissue inflammation affects insulin sensitivity and glucose tolerance. Low-grade, chronic adipose tissue inflammation is characterized by infiltration of macrophages and other immune cell populations into adipose tissue, and a shift toward more proinflammatory subtypes of leukocytes. The infiltration of proinflammatory cells in adipose tissue is associated with an increased production of key chemokines such as C-C motif chemokine ligand 2, proinflammatory cytokines including tumor necrosis factor α and interleukins 1β and 6 as well as reduced expression of the key insulin-sensitizing adipokine, adiponectin. In both rodent models and humans, adipose tissue inflammation is consistently associated with excess fat mass and insulin resistance. In humans, associations with insulin resistance are stronger and more consistent for inflammation in visceral as opposed to subcutaneous fat. Further, genetic alterations in mouse models of obesity that reduce adipose tissue inflammation are-almost without exception-associated with improved insulin sensitivity. However, a dissociation between adipose tissue inflammation and insulin resistance can be observed in very few rodent models of obesity as well as in humans following bariatric surgery- or low-calorie-diet-induced weight loss, illustrating that the etiology of insulin resistance is multifactorial. Taken together, adipose tissue inflammation is a key factor in the development of insulin resistance and type 2 diabetes in obesity, along with other factors that likely include inflammation and fat accumulation in other metabolically active tissues. © 2019 American Physiological Society. Compr Physiol 9:1-58, 2019.

C5aR1 interacts with TLR2 in osteoblasts and stimulates the osteoclast-inducing chemokine CXCL10

The anaphylatoxin C5a is generated upon activation of the complement system, a crucial arm of innate immunity. C5a mediates proinflammatory actions via the C5a receptor C5aR1 and thereby promotes host defence, but also modulates tissue homeostasis. There is evidence that the C5a/C5aR1 axis is critically involved both in physiological bone turnover and in inflammatory conditions affecting bone, including osteoarthritis, periodontitis, and bone fractures. C5a induces the migration and secretion of proinflammatory cytokines of osteoblasts. However, the underlying mechanisms remain elusive. Therefore, in this study we aimed to determine C5a‐mediated downstream signalling in osteoblasts. Using a whole‐genome microarray approach, we demonstrate that C5a activates mitogen‐activated protein kinases (MAPKs) and regulates the expression of genes involved in pathways related to insulin, transforming growth factor‐β and the activator protein‐1 transcription factor. Interestingly, using coimmunoprecipitation, we found an interaction between C5aR1 and Toll‐like receptor 2 (TLR2) in osteoblasts. The C5aR1‐ and TLR2‐signalling pathways converge on the activation of p38 MAPK and the generation of C‐X‐C motif chemokine 10, which functions, among others, as an osteoclastogenic factor. In conclusion, C5a‐stimulated osteoblasts might modulate osteoclast activity and contribute to immunomodulation in inflammatory bone disorders.

Anaphylatoxin Receptors C3aR and C5aR1 Are Important Factors That Influence the Impact of Ethanol on the Adipose Secretome

Background and aims: Chronic ethanol exposure results in inflammation in adipose tissue; this response is associated with activation of complement as well as the development of alcohol-related liver disease (ALD). Adipose communicates with other organs, including liver, via the release of soluble mediators, such as adipokines and cytokines, characterized as the "adipose secretome." Here we investigated the role of the anaphaylatoxin receptors C3aR and C5aR1 in the development of adipose tissue inflammation and regulation of the adipose secretome in murine ALD (mALD). Methods: Wild-type C57BL/6 (WT), C3aR ^-/-, and C5aR1 ^-/- mice were fed Lieber-DeCarli ethanol diet for 25 days (6% v/v, 32% kcal) or isocaloric control diets; indicators of inflammation and injury were assessed in gonadal adipose tissue. The adipose secretome was characterized in isolated adipocytes and stromal vascular cells. Results: Ethanol feeding increased the expression of adipokines, chemokines and leukocyte markers in gonadal adipose tissue from WT mice; C3aR ^-/- were partially protected while C5aR1 ^-/- mice were completely protected. In contrast, induction of CYP2E1 and accumulation of TUNEL-positive cells in adipose in response to ethanol feeding was independent of genotype. Bone marrow chimeras, generated with WT and C5aR1 ^-/- mice, revealed C5aR1 expression on non-myeloid cells, likely to be adipocytes, contributed to ethanol-induced adipose inflammation. Chronic ethanol feeding regulated both the quantity and distribution of adipokines secreted from adipocytes in a C5aR1-dependent mechanism. In WT mice, chronic ethanol feeding induced a predominant release of pro-inflammatory adipokines from adipocytes, while the adipose secretome from C5aR1 ^-/- mice was characterized by an anti-inflammatory/protective profile. Further, the cargo of adipocyte-derived extracellular vesicles (EVs) was distinct from the soluble secretome; in WT EVs, ethanol increased the abundance of pro-inflammatory mediators while EV cargo from C5aR1 ^-/- adipocytes contained a greater diversity and more robust expression of adipokines. Conclusions: C3aR and C5aR1 are potent regulators of ethanol-induced adipose inflammation in mALD. C5aR1 modulated the impact of chronic ethanol on the content of the adipose secretome, as well as influencing the cargo of an extensive array of adipokines from adipocyte-derived EVs. Taken together, our data demonstrate that C5aR1 contributes to ethanol-mediated changes in the adipose secretome, likely contributing to intra-organ injury in ALD.

Comparing the inflammatory profiles for incidence of diabetes mellitus and cardiovascular diseases: a prospective study exploring the 'common soil' hypothesis

Background

Chronic low-grade inflammation and associated insulin resistance and metabolic abnormalities have been proposed as ‘common soil’ for diabetes mellitus (DM) and cardiovascular disease (CVD). This paper aimed to investigate the inflammatory profiles of DM and CVD and to distinguish their shared and specific markers.

Methods

Based on the Malmö Diet and Cancer cohort, total and differential leukocyte counts were measured in 25,969 participants without previous DM or CVD and were studied in relation to incident DM (mean follow-up 17.4 ± 5.58 years) and incident CVD (i.e., coronary events, including fatal and nonfatal myocardial infarction, or stroke); mean follow-up 17.7 ± 5.46 years, using multivariable Cox regression models. Furthermore, plasma concentrations of another seven inflammatory markers were examined in relation to incident DM and incident CVD in a sub-cohort of 4658 participants. The associations of each inflammatory marker with incident DM versus incident CVD were compared using the Lunn–McNeil competing risks approach. In sensitivity analyses, those who developed both DM and CVD during follow-up were excluded.

Results

After adjustment for conventional risk factors, total and differential leukocyte counts, orosomucoid, and C-reactive protein were associated with an increased risk of both DM and CVD. Neutrophil to lymphocyte ratio, ceruloplasmin, alpha1-antitrypsin and soluble urokinase plasminogen activator receptor predicted increased risk of CVD but not DM, while haptoglobin and complement C3 showed the opposite pattern. In competing risks analyses, lymphocyte count and complement C3 had stronger associations with risk of DM than with risk of CVD (p for equal associations = 0.020 and 0.006). The reverse was true for neutrophil to lymphocyte ratio (p for equal associations = 0.025). Results were consistent in sensitivity analyses.

Conclusions

The results indicated substantial similarities in the inflammatory profiles associated with DM and CVD. However, there are also significant differences. These findings may help discriminate between individuals at elevated risk of DM and those at elevated risk of CVD, which is a prerequisite for targeted therapies.

Electronic supplementary material

The online version of this article (10.1186/s12933-018-0733-9) contains supplementary material, which is available to authorized users.

Diet-Induced Obesity Affects Muscle Regeneration After Murine Blunt Muscle Trauma-A Broad Spectrum Analysis

Injury to skeletal muscle affects millions of people worldwide. The underlying regenerative process however, is a very complex mechanism, time-wise highly coordinated, and subdivided in an initial inflammatory, a regenerative and a remodeling phase. Muscle regeneration can be impaired by several factors, among them diet-induced obesity (DIO). In order to evaluate if obesity negatively affects healing processes after trauma, we utilized a blunt injury approach to damage the extensor iliotibialis anticus muscle on the left hind limb of obese and normal weight C57BL/6J without showing any significant differences in force input between normal weight and obese mice. Magnetic resonance imaging (MRI) of the injury and regeneration process revealed edema formation and hemorrhage exudate in muscle tissue of normal weight and obese mice. In addition, morphological analysis of physiological changes revealed tissue necrosis, immune cell infiltration, extracellular matrix (ECM) remodeling, and fibrosis formation in the damaged muscle tissue. Regeneration was delayed in muscles of obese mice, with a higher incidence of fibrosis formation due to hampered expression levels of genes involved in ECM organization. Furthermore, a detailed molecular fingerprint in different stages of muscle regeneration underlined a delay or even lack of a regenerative response to injury in obese mice. A time-lapse heatmap determined 81 differentially expressed genes (DEG) with at least three hits in our model at all-time points, suggesting key candidates with a high impact on muscle regeneration. Pathway analysis of the DEG revealed five pathways with a high confidence level: myeloid leukocyte migration, regulation of tumor necrosis factor production, CD4-positive, alpha-beta T cell differentiation, ECM organization, and toll-like receptor (TLR) signaling. Moreover, changes in complement-, Wnt-, and satellite cell-related genes were found to be impaired in obese animals after trauma. Furthermore, histological satellite cell evaluation showed lower satellite cell numbers in the obese model upon injury. Ankrd1, C3ar1, Ccl8, Mpeg1, and Myog expression levels were also verified by qPCR. In summary, increased fibrosis formation, the reduction of Pax7⁺ satellite cells as well as specific changes in gene expression and signaling pathways could explain the delay of tissue regeneration in obese mice post trauma.

Vitamin D Insufficiency Predicts Elevated Levels of Complement 3 Independent of Insulin Resistance and BMI

This study was to determine serum 25-hydroxyvitamin D (25(OH)D), the complement 3 (C3), and C-reactive protein (CRP) levels, and their association with the risk of insulin resistance (IR). A case-control study was carried out among 134 participants with body mass index (BMI) ≥30 kg/m² and BMI=18.5-24.99 kg/m². Anthropometric and body composition indicators were measured. Serum levels of C3, CRP, 25(OH)D, insulin, and glucose were also measured. IR was assessed by the homeostasis model assessment (HOMA-IR). C3, CRP, insulin, and HOMA-IR levels were higher in participants with obesity than that of controls (p<0.001). After adjustment for the potential confounders, anthropometric and body composition indicators were correlated positively with C3 (p<0.001), and negatively with 25(OH)D (p<0.05). C3, and 25(OH)D were correlated with HOMA-IR (r=0.350; r=-0.212; p<0.05). In logistic regression analyses, C3 and CRP were significantly related to increased odds of IR among participants with obesity as compared to controls after progressively adjusting for the potential confounders (p<0.001), whereas 25(OH)D was negatively, but insignificantly, related to decreased odds of IR among participants with obesity (p>0.05). C3 was associated positively with 25(OH)D insufficiency/deficiency independent of HOMA-IR and/or BMI (β=0.183, p<0.05). Obesity is associated with elevated levels of proinflammatory biomarkers and IR. 25(OH)D insufficiency/deficiency was associated with C3 regardless of HOMA-IR or BMI, which could in turn, have a role in the augmentation of IR during obesity.

Anaphylatoxin C5a induces inflammation and reduces insulin sensitivity by activating TLR4/NF-kB/PI3K signaling pathway in 3T3-L1 adipocytes

Obesity closely correlates with metaflammation and characterizes with systemic-chronic-low inflammation. This study aims to evaluate effects of C5a on the inflammatory response and insulin resistance in 3T3-L1 adipocytes. 3T3-L1 pre-adipocytes were induced to the mature 3T3-L1 adipocytes. Then, 3T3-L1 were intervened with anaphylatoxin C5a, lipopolysaccharide (LPS) and C5a + LPS, respectively. Levels of Omentin, Chemerin, Vaspin and Apelin 12 in supernatants of medium were examined using ELISA. C5L2, C5a receptor (C5aR), I kappa B (IkB), IkB kinase (IKK), insulin receptor substrate 1 (IRS-1), IRS-2, PI3 K, p-PI3 K and β-actin were examined using RT-PCR and western blot assay, respectively. C5L2-C5aR colocalization was identified using immunofluorescence double label. NF-kB expression or activity was evaluated using electrophoretic mobility shift assay (EMSA), dual luciferase assay and immunofluorescence assay, respectively. The glucose uptake and insulin sensitivity were also evaluated. Results showed that C5a intervention significantly enhanced inflammatory molecule levels in supernatants of 3T3-L1 adipocytes. IKK inflammatory signaling pathway participated in C5a induced inflammation of 3T3-L1 adipocytes. C5a triggered the colocalization of C5L2 and C5aR and activated the NF-kB inflammatory signaling pathway. C5a intervention in 3T3-L1 adipocytes decreased the glucose uptake and resulted in reduction of insulin sensitivity. Insulin signaling pathway participated in C5a caused insulin sensitivity reduction. C5a intervention triggered the phosphorylation of PI3 K. In conclusion anaphylatoxin C5a induced inflammatory response by activating TLR4/NF-kB signaling pathway and generating C5L2-C5aR dimer, and caused insulin sensitivity reduction by activating PI3 K signaling pathway.

Sex-Specific Associations Between Complement Component 3 and Component 4 Levels and Metabolic Syndrome in an Adult Population

BACKGROUND

Metabolic syndrome (MetS) is a cluster of cardiovascular and metabolic risk factors in the same individual. Inflammation has been reported to be directly involved in the development of metabolic disease. Complement component 3 (C3) and complement component 4 (C4) have been identified as important inflammatory markers relevant to metabolic disease. However, few studies have analyzed the association between C3 and/or C4 and MetS. In this study, our aim is to evaluate sex-specific association between C3 and C4 levels and risk of MetS in an adult population.

METHODS

A cohort of 4635 adults was followed from 2010 to 2016. Serum C3 and C4 levels were measured using an immunonephelometric technique. MetS was defined by the American Heart Association scientific statements of 2009. Cox proportional hazard regression models were used to assess sex-specific association between C3 and C4 levels and the incidence of MetS.

RESULTS

During the ∼6 years of follow-up, 1445 new cases of MetS were identified. After being adjusted to confounding factors, the hazard ratios (95% confidence interval) of MetS for gradually increasing quintiles of C3 were 1.00, 1.23 (0.98-1.54), 1.50 (1.21-1.87), 1.64 (1.32-2.04), and 1.75 (1.41-2.18) (P for trend <0.0001) in men and 1.00, 0.96 (0.60-1.53), 1.61 (1.06-2.44), 2.01 (1.34-3.03), and 2.43 (1.63-3.63) (P for trend <0.0001) in women, respectively. Similar results were also obtained for gradually increasing quintiles of C4 in women, but not in men.

CONCLUSIONS

The levels of C3 were significantly associated with the incidence of MetS in both men and women. The levels of C4 contributed to risk of MetS only in women.

Mesenchymal stem cells alleviate acute kidney injury by down-regulating C5a/C5aR pathway activation

BACKGROUND

Acute kidney injury (AKI) leads to serious renal damage, and early inhibition of inflammation is necessary for its treatment. C5a/C5aR signaling activation promotes inflammatory response in tissue injury. Anti-inflammatory activity of mesenchymal stem cells (MSCs) makes it possible to alleviate AKI by controlling the C5a/C5aR signaling activation.

METHODS

Ischemia reperfusion (I/R)-induced AKI models in wild-type and C5aR KO mice were used. In addition, human bone marrow MSCs (hBM-MSCs) or C5aR antagonist were injected in this model. All animals were killed at 72 h after reperfusion. In vitro, the LPS-activated macrophage line RAW264.7 cells were co-cultured with or without hBM-MSCs in the presence of recombinant C5a or not for indicated time points. After that, C5aR expression, the inflammatory factor production, and NF-κB translocation in RAW264.7 cells were measured.

RESULTS

hBM-MSC treatment and C5a/C5aR signaling blockade or C5aR-deficiency exhibited similar attenuated effects on I/R-induced AKI, macrophages infiltration, and the pro-inflammatory cytokines TNF-α and IL-1β expression in renal tissues in mice. Moreover, hBM-MSC administration led to a significant reduction in C5a levels in serum and C5aR expression in the kidney tissues in mice after I/R. In vitro, upon co-culture with hBM-MSCs, both C5aR expression and the secretion of pro-inflammatory factors TNF-α, IL-6, and nitric oxide in LPS-activated macrophages were markedly reduced. Accordingly, recombinant complement C5a accelerated LPS-induced NF-κB translocation and pro-inflammatory factors expression in macrophages, but the addition of hBM-MSCs reversed these C5a-induced effects.

CONCLUSIONS

The present study indicates that hBM-MSCs alleviate AKI via suppressing C5a/C5aR-NF-κB pathway activation.

Serum complement factor 5a levels are associated with nonalcoholic fatty liver disease in obese children

AIM

Nonalcoholic fatty liver disease (NAFLD) is a leading cause of progressive and chronic liver injury. Complement factor 5a (C5a) may be involved in many inflammation disorders. This study investigated levels of systemic C5a in patients with and without NAFLD and lean controls.

METHODS

A cross-sectional study was conducted from July 2012 to June 2013 among 96 Chinese children, aged 6-17 years, recruited from the Pediatric Department of the Second Affiliated Hospital of Xi'an Jiao Tong University: 40 obese children with NAFLD, 31 obese children without NAFLD and 25 lean controls. Anthropometric parameters, clinical data and circulating C5a levels were measured.

RESULTS

Obese children had higher serum concentrations of complement factor C5a compared with lean controls, especially in obese children with NAFLD. C5a was positively correlated with body mass index (BMI), waist circumference, diastolic blood pressure (BP), triglycerides and homoeostasis model of insulin resistance, independent of their body mass index standard deviations score and age. Of the well-known risk factors, C5a was a significant predictor of NAFLD in obese children.

CONCLUSION

Serum C5a was elevated in obese children, especially in those with NAFLD and it may be proposed as a novel marker to predict advanced disease.

C3aR and C5aR1 act as key regulators of human and mouse β-cell function

AIMS

Complement components 3 and 5 (C3 and C5) play essential roles in the complement system, generating C3a and C5a peptides that are best known as chemotactic and inflammatory factors. In this study we characterised islet expression of C3 and C5 complement components, and the impact of C3aR and C5aR1 activation on islet function and viability.

MATERIALS AND METHODS

Human and mouse islet mRNAs encoding key elements of the complement system were quantified by qPCR and distribution of C3 and C5 proteins was determined by immunohistochemistry. Activation of C3aR and C5aR1 was determined using DiscoverX beta-arrestin assays. Insulin secretion from human and mouse islets was measured by radioimmunoassay, and intracellular calcium ([Ca2+]i), ATP generation and apoptosis were assessed by standard techniques.

RESULTS

C3 and C5 proteins and C3aR and C5aR1 were expressed by human and mouse islets, and C3 and C5 were mainly localised to β- and α-cells. Conditioned media from islets exposed for 1 h to 5.5 and 20 mM glucose stimulated C3aR and C5aR1-driven beta-arrestin recruitment. Activation of C3aR and C5aR1 potentiated glucose-induced insulin secretion from human and mouse islets, increased [Ca2+]i and ATP generation, and protected islets against apoptosis induced by a pro-apoptotic cytokine cocktail or palmitate.

CONCLUSIONS

Our observations demonstrate a functional link between activation of components of the innate immune system and improved β-cell function, suggesting that low-level chronic inflammation may improve glucose homeostasis through direct effects on β-cells.

Complement in cancer: untangling an intricate relationship

In tumour immunology, complement has traditionally been considered as an adjunctive component that enhances the cytolytic effects of antibody-based immunotherapies, such as rituximab. Remarkably, research in the past decade has uncovered novel molecular mechanisms linking imbalanced complement activation in the tumour microenvironment with inflammation and suppression of antitumour immune responses. These findings have prompted new interest in manipulating the complement system for cancer therapy. This Review summarizes our current understanding of complement-mediated effector functions in the tumour microenvironment, focusing on how complement activation can act as a negative or positive regulator of tumorigenesis. It also offers insight into clinical aspects, including the feasibility of using complement biomarkers for cancer diagnosis and the use of complement inhibitors during cancer treatment.

The role of complement system in adipose tissue-related inflammation

As the common factor linking adipose tissue to the metabolic context of obesity, insulin resistance and atherosclerosis are associated with a low-grade chronic inflammatory status, to which the complement system is an important contributor. Adipose tissue synthesizes complement proteins and is a target of complement activation. C3a-desArg/acylation-stimulating protein stimulates lipogenesis and affects lipid metabolism. The C3a receptor and C5aR are involved in the development of adipocytes' insulin resistance through macrophage infiltration and the activation of adipose tissue. The terminal complement pathway has been found to be instrumental in promoting hyperglycemia-associated tissue damage, which is characteristic of the major vascular complications of diabetes mellitus and diabetic ketoacidosis. As a mediator of the effects of the terminal complement complex C5b-9, RGC-32 has an impact on energy expenditure as well as lipid and glucose metabolic homeostasis. All of this evidence, taken together, indicates an important role for complement activation in metabolic diseases.

Longitudinal associations of the alternative and terminal pathways of complement activation with adiposity: The CODAM study

OBJECTIVE

To investigate longitudinal associations of components of the alternative (C3, C3a, Bb, factor D [FD], factor H [FH], and properdin) and the terminal complement pathway (C5a, sC5b-9) with adiposity.

METHODS

A prospective human cohort study (n=574 at baseline, n=489 after 7 years follow-up) was analyzed. Generalized estimating equations were used to evaluate the longitudinal associations between complement components (standardized values) and adiposity (main outcome BMI [kg/m²]). Multiple linear regression models were used to investigate the associations between change in complement levels and change in BMI. Analyses were adjusted for age, sex, medication and lifestyle.

RESULTS

Over the 7-year period, baseline C3 was positively associated with BMI (β=1.72 [95% confidence interval (CI): 1.35; 2.09]). Positive associations were also observed for C3a (β=0.64 [0.31; 0.97]), FD (β=1.00 [0.59; 1.42]), FH (β=1.17 [0.82; 1.53]), and properdin (β=0.60 [0.28; 0.92]), but not for Bb, C5a or sC5b-9. Moreover, changes in C3 (β=0.52 [0.34; 0.71]) and FH (β=0.51 [0.32; 0.70]) were significantly associated with changes in BMI.

CONCLUSIONS

The complement system, particularly activation of the alternative pathway, may be involved in development of adiposity. Whether individual aspects of alternative pathway activation have a causal role in human obesity, remains to be investigated.

Complement 3 serum levels as a pro-inflammatory biomarker for insulin resistance in obesity

INTRODUCTION

Obesity is frequently characterized by chronic inflammation and insulin resistance (IR). Obesity-associated inflammation is responsible for the complement system activation of which the third component (C3) plays the central role.

OBJECTIVE

to discuss several aspects of the central component of the complement system in relation to obesity and obesity-associated IR.

METHODS

A critical review of the relevant published English articles from 2003- 2014 was carried out using several search engines including PubMed, Google Scholar, and ScienceDirect. Keywords were used, including complement system, C3, obesity-induced inflammation, IR, ASP, and adipose tissue.

CONCLUSION

The defect in the adipose tissue secretory function during obesity may result in different metabolic disorders including IR. The C3 role during obesity-associated inflammation in IR is emerging. More longitudinal studies are warranted to evaluate the role of C3 among other pro-inflammatory biomarkers for IR.

Comparing the diagnostic ability of inflammatory markers in metabolic syndrome

BACKGROUND

Chronic low-grade inflammation contributes to the pathogenesis of the metabolic syndrome (MetS). Although some studies have demonstrated that several standard inflammatory markers provide diagnostic value for MetS, few studies have compared the diagnostic ability of various inflammatory markers. We demonstrated the diagnostic ability of several inflammatory markers in detecting MetS.

METHODS

Complement component 3 (C3), C4, high-sensitivity C-reactive protein (hs-CRP), leukocyte count, neutrophil, lymphocyte and neutrophil-to-lymphocyte ratio (NLR) concentrations were measured in 6312 participants living in Tianjin, China. MetS was defined according to American Heart Association criteria. Adjusted logistic models were used to assess associations between inflammatory markers and MetS. Receiver operating characteristic (ROC) curves were performed to determine the diagnostic values of inflammatory markers for MetS.

RESULTS

The adjusted odds ratio (95% CI) of MetS for the highest inflammatory markers (C3, leukocyte, neutrophil, lymphocyte) quintile, when compared to the lowest quintile were 2.68 (2.12-3.38), 2.53 (2.05-3.11), 1.31 (1.06-1.62) and 1.94 (1.60-2.37), respectively. ROC analysis showed that the optimal cut-off values were 101.0mg/dl for C3 (Area under the ROC curve (AUC)=0.68), 5.41×1000cells/mm³ for leukocyte (AUC=0.63), 3.20×1000cells/mm³ for neutrophil (AUC=0.60) and 1.82×1000cells/mm³ for lymphocyte (AUC=0.62). No significant association was observed between the other inflammatory markers and MetS.

CONCLUSIONS

Among the inflammatory markers assessed in this population, C3 has the strongest diagnostic value in detecting MetS. Further studies are encouraged to determine the efficacy of applying C3 to diagnosis and treatment in the clinical setting.