The adipokine C1q/TNF-related protein-3 (CTRP-3) inhibits Toll-like receptor (TLR)-induced expression of Cathelicidin antimicrobial peptide (CAMP) in adipocytes

Obesity and insulinopenic type 2 diabetes differentially impact, bone phenotype, bone marrow adipose tissue, and serum levels of the cathelicidin-related antimicrobial peptide in mice

Obesity is a risk factor of developing type 2 diabetes (T2D) and metabolic complications, through systemic inflammation and insulin resistance. It has also been associated with increased bone marrow adipocytes along with increased bone fragility and fracture risk. However, the differential effects of obesity and T2D on bone fragility remain unclear. The cathelicidin-related antimicrobial peptide (CRAMP) is a multifunctional modulator of the innate immunity that has emerged as biomarker of cardiometabolic diseases. The aims of this study were i) to assess the differential impact between hyperinsulinemic obesity versus insulinopenic T2D, on bone phenotype and bone marrow adipose tissue (BMAT), and ii) to analyse the link with CRAMP expression and its circulating levels in the context of obesity and T2D. We used C57BL/6 J male mice models of obesity induced by high-fat diet (HFD), and of insulinopenic T2D induced by streptozotocin (STZ) treatment combined with HFD, reflecting the metabolic heterogeneity of the diseases. As compared to low-fat diet (LFD) control group after 16 weeks of feeding, the HFD mice exhibit a significant weight gain, moderate hyperglycaemia, impaired glucose tolerance and insulin sensitivity, and significant increase in serum insulin levels. This hyperinsulinemic obesity led to decreased trabecular (Tb.Th) and cortical thickness (Ct.Th) in the tibia, associated with significant BMAT expansion, in addition to increased subcutaneaous (SCAT) and visceral adipose tissue (VAT). No changes were observed in the circulating levels of CRAMP peptide neither in other bone parameters. While, STZ treatment in HFD/STZ group induced a more severe hyperglycaemia, glucose intolerance and insulin resistance, and hypoinsulinemia. We also observed a negative effect on the expansion of both SCAT and VAT, as well as lower increase in BMAT as compared to HFD group. However, these mice with insulinopenic T2D exhibit early decrease in trabecular number (Tb.N) in proximal tibia, progressively from 8 to 16 weeks of protocol, and impaired femoral biomechanical stiffness. These alterations are also accompanied with decreased circulating levels of the CRAMP peptide in the HFD/STZ mice. The CRAMP mRNA levels decreased in VAT of both HFD and HFD/STZ groups. Overall, these results provide novel insights into the differential negative impact of obesity versus T2D on bone microenvironment, and suggest a link between hyperglycaemia-induced bone quality alterations during insulinopenia, and impaired regulation of the cathelicidin peptide of the innate immunity. Further investigations are needed to elucidate this relationship.

Cathelicidin: Insights into Its Impact on Metabolic Syndrome and Chronic Inflammation

Background/Objectives: LL-37 is associated with metabolic syndrome (MetS), a constellation of risk factors comprising obesity, insulin resistance (IR), dyslipidemia, and hypertension, which elevates the risk of cardiovascular disease and type 2 diabetes. Methods: In this narrative review, we analyzed the literature focusing on recent developments in the relationship between cathelicidin and various components of MetS to provide a comprehensive overview. Results: Studies have shown that LL-37 is linked to inflammation in adipose tissue (AT) and the development of IR in obesity. Cathelicidin can enhance inflammation by activating pro-inflammatory genes, as well as modulate the inflammatory response. The mechanisms of IR include the activation of complex signaling pathways that induce inflammation and reduce insulin signaling in adipocytes. The activation of Toll-like receptors (TLRs) by cathelicidin stimulates the secretion of pro-inflammatory cytokines, contributing to the disruption of insulin function in adipose cells. Cathelicidin also influences lipid metabolism, with recent research showing a negative relationship between LL-37 levels and HDL cholesterol. Therefore, LL-37 is involved not only in the regulation of inflammation but also in lipid metabolism, potentially aggravating the cardiovascular complications associated with MetS. Conclusions: Cathelicidin plays a crucial role in regulating the balance between inflammatory and anti-inflammatory responses in MetS. Understanding the impact of LL-37 on these mechanisms may unveil novel approaches for addressing MetS and its associated complications.

Regulation of Cathelicidin Antimicrobial Peptide (CAMP) Gene Expression by TNFα and cfDNA in Adipocytes

Understanding the complex interactions between metabolism and the immune system ("metaflammation") is crucial for the identification of key immunomodulatory factors as potential therapeutic targets in obesity and in cardiovascular diseases. Cathelicidin antimicrobial peptide (CAMP) is an important factor of innate immunity and is expressed in adipocytes. CAMP, therefore, might play a role as an adipokine in metaflammation and adipose inflammation. TNFα, cell-free nucleic acids (cfDNA), and toll-like receptor (TLR) 9 are components of the innate immune system and are functionally active in adipose tissue. The aim of the present study was to investigate the impact of TNFα and cfDNA on CAMP expression in adipocytes. Since cfDNA acts as a physiological TLR9 agonist, we additionally investigated TLR9-mediated CAMP regulation in adipocytes and adipose tissue. CAMP gene expression in murine 3T3-L1 and human SGBS adipocytes and in murine and human adipose tissues was quantified by real-time PCR. Adipocyte inflammation was induced in vitro by TNFα and cfDNA stimulation. Serum CAMP concentrations in TLR9 knockout (KO) and in wildtype mice were quantified by ELISA. In primary adipocytes of wildtype and TLR9 KO mice, CAMP gene expression was quantified by real-time PCR. CAMP gene expression was considerably increased in 3T3-L1 and SGBS adipocytes during differentiation. TNFα significantly induced CAMP gene expression in mature adipocytes, which was effectively antagonized by inhibition of PI3K signaling. Cell-free nucleic acids (cfDNA) significantly impaired CAMP gene expression, whereas synthetic agonistic and antagonistic TLR9 ligands had no effect. CAMP and TLR9 gene expression were correlated positively in murine and human subcutaneous but not in intra-abdominal/visceral adipose tissues. Male TLR9 knockout mice exhibited lower systemic CAMP concentrations than wildtype mice. CAMP gene expression levels in primary adipocytes did not significantly differ between wildtype and TLR9 KO mice. These findings suggest a regulatory role of inflammatory mediators, such as TNFα and cfDNA, in adipocytic CAMP expression as a novel putative molecular mechanism in adipose tissue innate immunity.

Multi-faceted roles of C1q/TNF-related proteins family in atherosclerosis

Purpose of review

C1q/TNF-related proteins (CTRPs) are involved in the modulation of the development and prognosis of atherosclerosis (AS). Here, we summarizes the pathophysiological roles of individual members of the CTRP superfamily in the development of AS. Currently, there is no specific efficacious treatment for AS-related diseases, therefore it is urgent to develop novel therapeutic strategies aiming to target key molecules involved in AS.

Recent findings

Recently, mounting studies verified the critical roles of the CTRP family, including CTRP1-7, CTRP9 and CTRP11-15, in the development and progression of AS by influencing inflammatory response, modulating glucose and lipid metabolism, regulating endothelial functions and the proliferation of vascular smooth muscle cells (VSMCs).

Conclusions

CTRP family regulate different pathophysiology stages of AS. CTRP3, CTRP9, CTRP12, CTRP13 and CTRP15 play a clear protective role in AS, while CTRP5 and CTRP7 play a pro-atherosclerotic role in AS. The remarkable progress in our understanding of CTRPs' role in AS will provide an attractive therapeutic target for AS.

Circulating Concentrations of Cathelicidin Anti-Microbial Peptide (CAMP) Are Increased during Oral Glucose Tolerance Test

Recent investigation has revealed the significant role of Cathelicidin antimicrobial peptide (CAMP) in infection defense and innate immunity processes in adipose tissue. Meanwhile, knowledge of its regulation and functions in metabolic contexts as an adipokine remains sparce. The present study investigated the postprandial regulation of circulating CAMP levels during oral glucose tolerance tests (OGTTs). Eighty-six metabolically healthy volunteers participated in a standardized 75 g-2 h-OGTT setting. The effects of exogenous glucose, insulin, and incretins on CAMP expression in human adipocyte culture (cell-line SGBS) were studied in vitro. CAMP concentrations in blood serum samples were measured by ELISA techniques and adipocyte gene expression levels were quantified by real-time PCR. Of note, base-line CAMP serum quantities were negatively correlated with HDL cholesterol levels as well as with the anti-inflammatory adipokine adiponectin. During the 2 h following glucose ingestion, a significant rise in circulating CAMP concentrations was observed in considerable contrast to reduced quantities of fatty acid binding proteins (FABP) 2 and 4 and dipeptidyl peptidase 4 (DPP4). In SGBS adipocytes, neither differing glucose levels nor insulin or incretin treatment significantly induced CAMP mRNA levels. According to our data, glucose represents a positive postprandial regulator of systemic CAMP. This effect apparently is not mediated by the regulatory impact of glucose metabolism on adipocyte CAMP expression.

CTRP family in diseases associated with inflammation and metabolism: molecular mechanisms and clinical implication

C1q/tumor necrosis factor (TNF) related proteins (CTRPs) is a newly discovered adipokine family with conservative structure and ubiquitous distribution and is secreted by adipose tissues. Recently, CTRPs have attracted increasing attention due to the its wide-ranging effects upon inflammation and metabolism. To-date, 15 members of CTRPs (CTRP1-15) with the characteristic C1q domain have been characterized. Earlier in-depth phenotypic analyses of mouse models of CTRPs deficiency have also unveiled ample function of CTRPs in inflammation and metabolism. This review focuses on the rise of CTRPs, with a special emphasis on the latest discoveries with regards to the effects of the CTRP family on inflammation and metabolism as well as related diseases. We first introduced the structure of characteristic domain and polymerization of CTRPs to reveal its pleiotropic biological functions. Next, intimate association of CTRP family with inflammation and metabolism, as well as the involvement of CTRPs as nodes in complex molecular networks, were elaborated. With expanding membership of CTRP family, the information presented here provides new perspectives for therapeutic strategies to improve inflammatory and metabolic abnormalities.

Human C1q Tumor Necrosis Factor 8 (CTRP8) defines a novel tryptase+ mast cell subpopulation in the prostate cancer microenvironment

The adipokine C1q Tumor Necrosis Factor 8 (CTRP8) is the least known member of the 15 CTRP proteins and a ligand of the relaxin receptor RXFP1. We previously demonstrated the ability of the CTRP8-RXFP1 interaction to promote motility, matrix invasion, and drug resistance. The lack of specific tools to detect CTRP8 protein severely limits our knowledge on CTRP8 biological functions in normal and tumor tissues. Here, we have generated and characterized the first specific antiserum to human CTRP8 which identified CTRP8 as a novel marker of tryptase+ mast cells (MC_T) in normal human tissues and in the prostate cancer (PC) microenvironment. Using human PC tissue microarrays composed of neoplastic and corresponding tumor-adjacent prostate tissues, we have identified a significantly higher number of CTRP8+ MC_T in the peritumor versus intratumor compartment of PC tissues of Gleason scores 6 and 7. Higher numbers of CTRP8+ MC_T correlated with the clinical parameter of biochemical recurrence. We showed that the human MC line ROSA^{KIT WT} expressed RXFP1 transcripts and responded to CTRP8 treatment with a small but significant increase in cell proliferation. Like the cognate RXFP1 ligand RLN-2 and the small molecule RXFP1 agonist ML-290, CTRP8 reduced degranulation of ROSA^{KIT WT} MC stimulated by the Ca²⁺-ionophore A14187. In conclusion, this is the first report to identify the RXFP1 agonist CTRP8 as a novel marker of MC_T and autocrine/paracrine oncogenic factor within the PC microenvironment.

Plasma C1q/tumor necrosis factor-related protein-3 concentrations are associated with diabetic peripheral neuropathy

INTRODUCTION

To analyze the associations of circulating C1q/tumor necrosis factor-related protein-3 (CTRP3) concentrations with several metabolic parameters and to investigate the possible role of CTRP3 in subjects with diabetic peripheral neuropathy (DPN).

RESEARCH DESIGN AND METHODS

A total of 347 participants were recruited in this study, and plasma CTRP3 concentrations were analyzed in subjects with DPN (n=172) and without DPN (non-DPN, n=175). The nerve conduction test and oral glucose tolerance test were performed, and Neuropathy Symptom Score (NSS)/Neuropathy Disability Score (NDS) and biochemical parameters were measured in all participants.

RESULTS

Plasma CTRP3 concentrations were significantly lower in patients with DPN compared with those in patients with diabetes without DPN (p<0.01), despite the comparable glucose and lipid metabolism levels in both groups. Groups with a higher plasma CTRP3 level had a faster nerve conduction velocity. In addition, plasma CTRP3 concentrations were negatively correlated with hemoglobin A1c (HbA1c), urea acid (UA), triglyceride, NSS and NDS (p<0.05) after being adjusted for age and sex. Multivariate logistic regression analysis revealed that plasma CTRP3 concentrations were significantly correlated with DPN after being controlled for age, sex, body mass index, HbA1c, blood pressure, lipid profiles, and renal function.

CONCLUSIONS

Plasma CTRP3 concentrations were significantly lower in patients with DPM and positively correlated with nerve conduction velocity. The relationship between CTRP3 levels and DPN is independent of the glucose and lipid status. Therefore, circulating CTRP3 might serve as a predictor of impairment of nerve conduction in patients with DPN.