C5a receptor deficiency alters energy utilization and fat storage

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.

Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retinal pigment epithelial cells to oxidative stress

Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide induced mitochondrial elongation. In contrast, oxidatively stressed cells (H2O2) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and - 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

Microglia refine developing retinal astrocytic and vascular networks through the complement C3/C3aR axis

Microglia, a resident immune cell of the central nervous system (CNS), play a pivotal role in facilitating neurovascular development through mechanisms that are not fully understood. Previous reports indicate a role for microglia in regulating astrocyte density. This current work resolves the mechanism through which microglia facilitate astrocyte spatial patterning and superficial vascular bed formation in the neuroretina during development. Ablation of microglia increased astrocyte density and altered spatial patterning. Mechanistically, we show that microglia regulate the formation of the spatially organized astrocyte template required for subsequent vascular growth, through the complement C3/C3aR axis during neuroretinal development. Lack of C3 or C3aR hindered the developmental phagocytic removal of astrocyte bodies and resulted in increased astrocyte density. In addition, increased astrocyte density was associated with elevated proangiogenic extracellular matrix gene expression in C3- and C3aR-deficient retinas, resulting in increased vascular density. These data demonstrate that microglia regulate developmental astrocyte and vascular network spatial patterning in the neuroretina via the complement axis.

Genetics of Familial Combined Hyperlipidemia (FCHL) Disorder: An Update

Familial combined hyperlipidemia (FCHL) is one of the most common familial lipoprotein disorders of the lipoproteins, with a prevalence of 0.5% to 2% in different populations. About 10% of these patients suffer from cardiovascular disease and this number is increased by up to 11.3% in the young survivors of myocardial infarction and by 40% among all the survivors of myocardial infarction. Although initially thought to be that FCHL has an inheritance pattern of monogenic, the disease's etiology is still not fully understood and it appears that FCHL has a complex pattern related to genetic variants, environmental factors, and lifestyles. Two strategies have been used to identify its complex genetic background: candidate gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL with a variable degree of scientific evidence. Until now, more than 30 different genetic variants have been identified related to FCHL. In this study, we aimed to review the individual genes that have been described in FCHL and how these genes and variants can be related to the current concept of metabolic pathways resulting in familial combined hyperlipidemia.

Humoral immunity in atherosclerosis and myocardial infarction: from B cells to antibodies

Immune mechanisms are critically involved in the pathogenesis of atherosclerosis and its clinical manifestations. Associations of specific antibody levels and defined B cell subsets with cardiovascular disease activity in humans as well as mounting evidence from preclinical models demonstrate a role of B cells and humoral immunity in atherosclerotic cardiovascular disease. These include all aspects of B cell immunity, the generation of antigen-specific antibodies, antigen presentation and co-stimulation of T cells, as well as production of cytokines. Through their impact on adaptive and innate immune responses and the regulation of many other immune cells, B cells mediate both protective and detrimental effects in cardiovascular disease. Several antigens derived from (oxidised) lipoproteins, the vascular wall and classical autoantigens have been identified. The unique antibody responses they trigger and their relationship with atherosclerotic cardiovascular disease are reviewed. In particular, we focus on the different effector functions of specific IgM, IgG, and IgE antibodies and the cellular responses they trigger and highlight potential strategies to target B cell functions for therapy.

Complement and human T cell metabolism: Location, location, location

The complement system represents one of the evolutionary oldest arms of our immune system and is commonly recognized as a liver-derived and serum-active system critical for providing protection against invading pathogens. Recent unexpected findings, however, have defined novel and rather "uncommon" locations and activities of complement. Specifically, the discovery of an intracellularly active complement system-the complosome-and its key role in the regulation of cell metabolic pathways that underly normal human T cell responses have taught us that there is still much to be discovered about this system. Here, we summarize the current knowledge about the emerging functions of the complosome in T cell metabolism. We further place complosome activities among the non-canonical roles of other intracellular innate danger sensing systems and argue that a "location-centric" view of complement evolution could logically justify its close connection with the regulation of basic cell physiology.

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.

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.

Impaired insulin signaling in the B10.D2-Hc0 H2d H2-T18c/oSnJ mouse model of complement factor 5 deficiency

Given the chemoattractant potential of complement factor 5 (C5) and its increased expression in adipose tissue (AT) of obese mice, we determined whether this protein of the innate immune system impacts insulin action. C5 control (C5cont) and spontaneously C5-deficient (C5def, B10.D2-Hc0 H2d H2-T18c/oSnJ) mice were placed on low- and high-fat diets to investigate their inflammatory and metabolic phenotypes. Adenoviral delivery was used to evaluate the effects of exogenous C5 on systemic metabolism. C5def mice gained less weight than controls while fed a high-fat diet, accompanied by reduced AT inflammation, liver mass, and liver triglyceride content. Despite these beneficial metabolic effects, C5def mice demonstrated severe glucose intolerance and systemic insulin resistance, as well as impaired insulin signaling in liver and AT. C5def mice also exhibited decreased expression of insulin receptor (INSR) gene and protein, as well as improper processing of pro-INSR. These changes were not due to the C5 deficiency alone as other C5-deficient models did not recapitulate the INSR processing defect; rather, in addition to the mutation in the C5 gene, whole genome sequencing revealed an intronic 31-bp deletion in the Insr gene in the B10.D2-Hc0 H2d H2-T18c/oSnJ model. Irrespective of the genetic defect, adenoviral delivery of C5 improved insulin sensitivity in both C5cont and C5def mice, indicating an insulin-sensitizing function of C5.

Targeting Inflammatory Pathways in Alzheimer's Disease: A Focus on Natural Products and Phytomedicines

Studies of the brains of Alzheimer's disease (AD) patients have revealed key neuropathological features, such as the deposition of aggregates of insoluble amyloid-β (Aβ) peptides and neurofibrillary tangles (NFTs). These pathological protein deposits, including Aβ peptides (which form senile plaques) and hyperphosphorylated tau (which aggregates into NFTs), have been assumed to be 'the cause of AD'. Aβ has been extensively targeted to develop an effective disease-modifying therapy, but with limited clinical success. Emerging therapies are also now targeting further pathological processes in AD, including neuroinflammation. This review focuses on the inflammatory and oxidative stress-related changes that occur in AD, and discusses some emerging anti-inflammatory natural products and phytomedicines. Many of the promising compounds are cytokine-suppressive anti-inflammatory drugs (CSAIDs), which target the proinflammatory AP1 and nuclear factor-κB signalling pathways and inhibit the expression of many proinflammatory cytokines, such as interleukin (IL)-1, IL-6, tumour necrosis factor-α, or nitric oxide produced by inducible nitric oxide synthase. However, many of these phytomedicines have not been tested in rigorous clinical trials in AD patients. It is not yet clear if the active compounds reach an effective concentration in the brain (due to limited bioavailability) or if they can slow down AD progression in long-term trials. The authors suggest that it is crucial for both the pharmacological and complementary medicine industries to conduct and fund those studies to significantly advance the field.

Chronic exposure to gamma irradiation at low-dose rates accelerates blood pressure decline associated with aging in female B6C3F1 mice

PURPOSE

Many studies are focusing on the biological effects of gamma irradiation at low-dose rates. Studies have shown that chronic exposure to gamma irradiation at low-dose rates shortened the lifespan of mice due to neoplasm formation. The aim of this study was to clarify the physiological effects of long-term exposure to gamma irradiation at low-dose rates in mice, measured with noninvasive parameters such as blood pressure.

MATERIALS AND METHODS

Specific-pathogen-free female B6C3F₁ mice were irradiated with gamma rays at a low dose of 20 mGy/day - a dose rate shown to shorten the life span in previous studies. The blood pressure parameters (systolic, diastolic, and mean blood pressure), heart rate, tail blood volume, and blood flow of the mice were measured every 7 weeks. Age-matched, non-irradiated mice were used as controls.

RESULTS AND CONCLUSION

The blood pressure levels of the irradiated mice decreased at an earlier age compared to the non-irradiated control mice. The expression levels of the marker genes of aging that are also associated with regulation of blood pressure showed significant differences between non-irradiated and irradiated mice. These results indicated that long-term exposure to gamma irradiation at low-dose rates induce the expression levels of Rap1a and reduces Panx1 and Sirt3, which may have contributed to the accelerated blood pressure decline in female mice.

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.

Keeping It All Going-Complement Meets Metabolism

The complement system is an evolutionary old and crucial component of innate immunity, which is key to the detection and removal of invading pathogens. It was initially discovered as a liver-derived sentinel system circulating in serum, the lymph, and interstitial fluids that mediate the opsonization and lytic killing of bacteria, fungi, and viruses and the initiation of the general inflammatory responses. Although work performed specifically in the last five decades identified complement also as a critical instructor of adaptive immunity—indicating that complement’s function is likely broader than initially anticipated—the dominant opinion among researchers and clinicians was that the key complement functions were in principle defined. However, there is now a growing realization that complement activity goes well beyond “classic” immune functions and that this system is also required for normal (neuronal) development and activity and general cell and tissue integrity and homeostasis. Furthermore, the recent discovery that complement activation is not confined to the extracellular space but occurs within cells led to the surprising understanding that complement is involved in the regulation of basic processes of the cell, particularly those of metabolic nature—mostly via novel crosstalks between complement and intracellular sensor, and effector, pathways that had been overlooked because of their spatial separation. These paradigm shifts in the field led to a renaissance in complement research and provide new platforms to now better understand the molecular pathways underlying the wide-reaching effects of complement functions in immunity and beyond. In this review, we will cover the current knowledge about complement’s emerging relationship with the cellular metabolism machinery with a focus on the functional differences between serum-circulating versus intracellularly active complement during normal cell survival and induction of effector functions. We will also discuss how taking a closer look into the evolution of key complement components not only made the functional connection between complement and metabolism rather “predictable” but how it may also give clues for the discovery of additional roles for complement in basic cellular processes.

Association of C5aR1genetic polymorphisms with coronary artery disease in a Han population in Xinjiang, China

Background

Complement 5a receptor (C5aR) was demonstrated a receptor of complement 5a (C5a) which is involved in many inflammatory diseases. The functional responses attributed to C5a results from its interaction with its receptors C5aR, which stimulates food intake, plays a role in increasing the inflammatory response in adipose tissue as well as the cardiovascular and neural systems. However, There are unknown associations between the SNPs of C5aR1 gene and coronary artery disease (CAD).

Methods

We examined the role of the tagging single nucleotide polymorphisms (SNPs) of C5aR1 gene for CAD using a case–control design, and determined the prevalence of C5aR1 genotypes in 505 CAD patients and 469 age and sex-matched healthy control subjects of Han population.

Results

The rs10853784 was found to be associated with CAD in dominant model (CC vs TT + CT, P = 0.004). The difference remained statistically significant after multivariate adjustment (OR = 1.430, 95% CI: 1.087 ~ 1.882, P = 0.011). There was no significant difference in genotype distributions of rs4577202 and rs7250152 between CAD patients and control subjects. The frequency of the haplotype (A-T-C) was significantly higher in the CAD patients than in the controls (P = 0.035), and the haplotype (A-C-T) was significantly lower in the CAD patients than in the control subjects in Chinese Han population (P = 0.002).

Conclusion

The results of this study indicate that rs10853784 of C5aR1 gene are associated with CAD in Han population of China, and A-C-T haplotypes may be protective genetic marker and the A-T-C may be risk genetic marker for CAD in Chinese Han population.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2054871241495194.

High expression of C5L2 correlates with high proinflammatory cytokine expression in advanced human atherosclerotic plaques

The complement anaphylatoxin C5a functions through its two receptors, C5aR (CD88) and C5a receptor-like 2 (C5L2). Their role in atherosclerosis is incompletely understood. We, therefore, analyzed C5aR and probed the yet unknown expression and function of C5L2 in human atherogenesis. Human atherosclerotic plaques obtained by endarterectomy were staged and analyzed for C5L2 and C5aR by IHC and quantitative real-time PCR. C5L2-expressing cells in plaques were mostly macrophages, less neutrophils and endothelial cells, as determined by double immunostaining. Although early influx of C5aR(+) cells was detected, C5L2 levels increased with lesion complexity and colocalized with C5aR and oxidized low-density lipoprotein. Gene expression of C5L2 and C5aR showed similar trends, such as the receptor-expressing cells. The expression of C5L2 in advanced lesions correlated with increased levels of IL-1β and tumor necrosis factor-α in plaques. Furthermore, in vitro experiments in macrophages from wild-type and C5l2- and C5ar-deficient mice corroborated the contributing role of C5l2 in oxidized low-density lipoprotein-pretreated C5a-induced cytokine expression, as measured by enzyme-linked immunosorbent assay. Finally, C5l2- and C5ar-deficient peripheral blood mononuclear cells showed less arrest on tumor necrosis factor-α-stimulated mouse endothelial cells in vitro when compared with wild-type controls. Taken together, prominent C5L2 expression in advanced atherosclerotic stages directly correlates with high levels of proinflammatory cytokines. This might indicate a proinflammatory role of C5L2 in atherosclerosis that needs to be pursued in the future by applying in vivo mouse models.

Downregulation of complement C3 and C3aR expression in subcutaneous adipose tissue in obese women

BACKGROUND

The central component of the complement system, C3, is associated with obesity, metabolic syndrome and cardiovascular disease however the underlying reasons are unknown. In the present study we evaluated gene expression of C3, the cleavage product C3a/C3adesArg and its cognate receptor C3aR in subcutaneous and omental adipose tissue in women.

METHODS

Women (n = 140, 21-69 years, BMI 19.5-79 kg/m2) were evaluated for anthropometric and blood parameters, and adipose tissue gene expression.

RESULTS

Subjects were separated into groups (n = 34-36) according to obesity: normal/overweight (≤30 kg/m2), obese I (≤45 kg/m2), obese II (≤51 kg/m2), and obese III (≤80 kg/m2). Overall, while omental expression remained unchanged, subcutaneous C3 and C3aR gene expression decreased with increasing adiposity (2-way ANOVA, p<0.01), with a concomitant decrease in SC/OM ratio (p<0.001). In subcutaneous adipose, both C3 and C3aR expression correlated with apoB, and apoA1 and inversely with waist circumference and blood pressure, while C3aR also correlated with glucose (p<0.05-0.0001). While omental C3aR expression did not correlate with any factor, omental C3 correlated with waist circumference, glucose and apoB (all p<0.05). Further, while plasma C3a/C3adesArg increased and adiponectin decreased with increasing BMI, both correlated (C3a negatively and adiponectin positively) with subcutaneous C3 and C3aR expression (p<0.05-0.001) or less).

CONCLUSIONS

The obesity-induced down-regulation of complement C3 and C3aR which is specific to subcutaneous adipose tissue, coupled to the strong correlations with multiple anthropometric, plasma and adipokine variables support a potential role for complement in immunometabolism.

C5aR and C5L2 act in concert to balance immunometabolism in adipose tissue

Recent studies suggested that the immunometabolic receptors; C5aR and C5L2, constitutively self-associate into homo-/heterodimers and that acylation stimulating protein (ASP/C3adesArg) or C5a treatment of adipocytes increased their colocalization. The present study evaluates the C5aR contribution in adipocytes to the metabolic and immune responses elicited by ligand stimulation. The effects of C5a, ASP, and insulin on cytokine production, triglyceride synthesis (TGS), and key signaling pathways were evaluated in isolated primary adipocytes and cultured 3T3-L1 differentiated adipocytes. In addition, mRNA expression of IRS1 and PGC1α was compared in adipose tissue samples from WT vs. C5aRKO mice. Both C5a and ASP directly increased MCP-1 (238±4%; P<0.001, and 377±2% vs. basal 100%; P<0.001, respectively) and KC (413±11%; P<0.001, and 529±16%; P<0.001 vs. basal 100%, respectively) secretion, TGS (131±1%; P<0.001, and 152±6%; P<0.001, vs. basal 100% respectively), and Akt/NFκB phosphorylation pathways in adipocytes. However, in C5aRKO adipocytes, C5a effects were disrupted, while stimulatory effects of ASP were mostly maintained. Addition of C5a completely blocked ASP signaling and activity in both C5aRKO and WT adipocytes as well as 3T3-L1 adipocytes. Furthermore, C5aRKO adipocytes revealed impaired insulin stimulation of cytokine production, with partial impairment of signaling and TGS stimulation, consistent with decreased IRS1 and PGC1α mRNA expression in adipose tissue. These observations indicate the importance of C5aR in adipose tissue metabolism and immunity, which may be regulated through heterodimerization with C5L2.

Association of immune and metabolic receptors C5aR and C5L2 with adiposity in women

Adipose tissue receptors C5aR and C5L2 and their heterodimerization/functionality and interaction with ligands C5a and acylation stimulating protein (ASP) have been evaluated in cell and rodent studies. Their contribution to obesity factors in humans remains unclear. We hypothesized that C5a receptors, classically required for host defense, are also associated with adiposity. Anthropometry and fasting blood parameters were measured in 136 women divided by body mass index (BMI): normal/overweight (≤30 kg/m(2); n = 34), obese I (≤45 kg/m(2); n = 33), obese II (≤51 kg/m(2); n = 33), and obese III (≤80 kg/m(2); n = 36). Subcutaneous and omental adipose tissue C5aR and C5L2 expression were analysed. C5L2 expression was comparable between subcutaneous and omental across all BMI groups. Plasma ASP and ASP/omental C5L2 expression increased with BMI (P < 0.001 and P < 0.01, resp.). While plasma C5a was unchanged, C5aR expression decreased with increasing BMI in subcutaneous and omental tissues (P < 0.01 and P < 0.05, resp.), with subcutaneous omental depots. Omental C5L2/C5aR ratio increased with BMI (P < 0.01) with correlations between C5L2/C5aR and waist circumference, HDL-C, and adiponectin. Tissue and BMI differences in receptors and ligands, particularly in omental, suggest relationship to metabolic disturbances and highlight adipose-immune interactions.

Complement receptors C5aR and C5L2 are associated with metabolic profile, sex hormones, and liver enzymes in obese women pre- and postbariatric surgery

OBJECTIVE

Obesity is associated with metabolic dysfunction with sex differences and chronic, low-grade inflammation.We proposed that hepatic expression of immune complement C3 related receptors (C3aR, C5aR, and C5L2) would be associated with pre- or postmenopausal status and metabolic profile in severely obese women. We hypothesized that C5L2/C5aR ratio, potentially influencing the ASP/C5L2 metabolic versus C5a/C5aR immune response, would predict metabolic profiles after weight loss surgery.

MATERIALS AND METHODS

Fasting plasma (hormone, lipid, and enzyme analysis) and liver biopsies (RT-PCR gene expression) were obtained from 91 women during surgery.

RESULTS

Hepatic C5L2 mRNA expression was elevated in pre- versus postmenopausal women (P < 0.01) and correlated positively with circulating estradiol, estrone, ApoB, ApoA1, ApoA1/B, waist circumference, age, and LDL-C (all P < 0.05).While plasma ASP was lower in pre- versus postmenopausal women (P < 0.01), the hepatic C5L2/C5aR mRNA ratio was increased (P < 0.001) and correlated positively with estrone (P < 0.01) and estradiol (P < 0.001) and negatively with circulating ApoB and liver enzymes ALT, AST, and GGT (all P < 0.05). Over 12 months postoperatively, liver enzymes in low C5L2/C5aR mRNA ratio group remained higher (ALP and ALT, P < 0.05, AST and GGT, P < 0.001 2-way-ANOVA).

CONCLUSION

C5L2-C5aR association with other mediators including estrogens may contribute to hepatic metabolic and inflammatory function.

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

Obese adipose tissue (AT) inflammation contributes critically to development of insulin resistance. The complement anaphylatoxin C5a receptor (C5aR) has been implicated in inflammatory processes and as regulator of macrophage activation and polarization. However, the role of C5aR in obesity and AT inflammation has not been addressed. We engaged the model of diet-induced obesity and found that expression of C5aR was significantly upregulated in the obese AT, compared with lean AT. In addition, C5a was present in obese AT in the proximity of macrophage-rich crownlike structures. C5aR-sufficient and -deficient mice were fed a high-fat diet (HFD) or a normal diet (ND). C5aR deficiency was associated with increased AT weight upon ND feeding in males, but not in females, and with increased adipocyte size upon ND and HFD conditions in males. However, obese C5aR(-/-) mice displayed improved systemic and AT insulin sensitivity. Improved AT insulin sensitivity in C5aR(-/-) mice was associated with reduced accumulation of total and proinflammatory M1 macrophages in the obese AT, increased expression of IL-10, and decreased AT fibrosis. In contrast, no difference in β cell mass was observed owing to C5aR deficiency under an HFD. These results suggest that C5aR contributes to macrophage accumulation and M1 polarization in the obese AT and thereby to AT dysfunction and development of AT insulin resistance.