CTRP13 Preserves Endothelial Function by Targeting GTP Cyclohydrolase 1 in Diabetes

C1ql3 knockout affects microglia activation, neuronal integrity, and spontaneous behavior in Wistar rats

BACKGROUND

C1QL3 is widely expressed in the brain and is specifically produced by a subset of excitatory neurons. However, its function is still not clear. We established C1ql3-deficient rats to investigate the role of C1QL3 in the brain.

METHODS

C1ql3 knockout (KO) rats were generated using CRISPR/Cas9. C1ql3 KO was determined by polymerase chain reaction (PCR), DNA sequencing, and western blotting. Microglia morphology and cytokine expression with or without lipopolysaccharide (LPS) stimulus were analyzed using immunohistochemistry and real-time PCR. The brain structure changes in KO rats were examined using magnetic resonance imaging. Neuronal architecture alteration was analyzed by performing Golgi staining. Behavior was evaluated using the open field test, Morris water maze test, and Y maze test.

RESULTS

C1ql3 KO significantly increased the number of ramified microglia and decreased the number of hypertrophic microglia, whereas C1ql3 KO did not influence the expression of pro-inflammatory factors and anti-inflammatory factors except IL-10. C1ql3 KO brains had more amoeboid microglia types and higher Arg-1 expression compared with the WT rats after LPS stimulation. The brain weights and HPC sizes of C1ql3 KO rats did not differ from WT rats. C1ql3 KO damaged neuronal integrity including neuron dendritic arbors and spine density. C1ql3 KO rats demonstrated an increase in spontaneous activity and an impairment in short working memory.

CONCLUSIONS

C1ql3 KO not only interrupts the neuronal integrity but also affects the microglial activation, resulting in hyperactive behavior and impaired short memory in rats, which highlights the role of C1QL3 in the regulation of structure and function of both neuronal and microglial cells.

CTRP13 alleviates palmitic acid-induced inflammation, oxidative stress, apoptosis and endothelial cell dysfunction in HUVECs

C1q/tumor necrosis factor-related protein 13 (CTRP13) has been reported to participate in cardiovascular diseases. However, the role and molecular mechanism of CTRP13 in obesity-induced endothelial cell damage is still unclear. In palmitic acid (PA)-induced human umbilical vein endothelial cells (HUVECs), qRT-PCR and western blot were used to examine CTRP13 expression. CCK-8 and TUNEL assays were adopted to assess cell viability and apoptosis, respectively. ROS level and MDA content were evaluated by their commercial kits and inflammatory cytokines were measured using ELISA. Endothelial cell dysfunction was evaluated by detecting NO production and eNOS expression, and tube formation assay was performed to assess angiogenesis. AMPK pathway-related proteins were detected by western blot. The results showed that CTRP13 was downregulated in PA-induced HUVECs. CTRP13 overexpression reduced PA-induced cell viability loss and oxidative stress in HUVECs. Moreover, CTRP13 overexpression suppressed PA-induced inflammation and apoptosis, improved angiogenesis ability, and alleviated endothelial cell dysfunction in HUVECs. In addition, CTRP13 overexpression activated AMPK pathway and regulated the expressions of downstream NOX1/p38 and KLF2. Furthermore, compound C countervailed the impacts of CTRP13 overexpression on cell viability, oxidative stress, inflammation, apoptosis and endothelial function in PA-induced HUVECs. To sum up, CTRP13 overexpression may alleviate PA-induced endothelial cell damage.

Adiponectin C1q/Tumor Necrosis Factor-Related Protein 13 (CTRP13) Protects against Renal Inflammation and Fibrosis in Obstructive Nephropathy

Renal inflammation and fibrosis are the important pathological phenomena associated with obstructive nephropathy. However, the underlying mechanism associated with this disease has yet to be fully elucidated. The present study, therefore, aimed to investigate the effects mediated by C1q/tumor necrosis factor-related protein 13 (CTRP13) on renal inflammation and fibrosis in addition to elucidating the underlying mechanism. To meet this aim, a mouse unilateral ureteral obstruction (UUO)-mediated renal dysfunction model was established. In addition, hematoxylin-eosin staining (H&E) staining and immunofluorescence experiments as well as Western blotting and reverse transcription quantitative (RT q) PCR analyses were performed. Recombinant CTRP13 was used to investigate the role of CTRP13 in chronic renal inflammation and fibrosis. A decreased expression level of CTRP13 was identified in the plasma of patients with renal fibrosis and in UUO-model mice. The renal histopathological and functional analyses revealed that CTRP13 could both reverse UUO mediated renal dysfunction and ameliorate the conditions of tubulointerstitial fibrosis and tubular injury. Additionally, CTRP13 was found to inhibit the expression levels of extracellular matrix proteins and proinflammatory mediators. In terms of the underlying mechanism, the protective effects on inflammation and fibrosis of the kidneys of CTRP13-treated mice undergoing UUO were found to be associated with the inactivation of the TGF β/Smad and NF κB p65 signaling pathways. Taken together, these findings have suggested that CTRP13 fulfills a vital role in the progression of obstructive nephropathy, thereby uncovering brand new insights into possible leads for the therapeutic treatment of chronic kidney disease (CKD).

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.

Pleiotropy of C1QL proteins across physiological systems and their emerging role in synapse homeostasis

The C1q/TNF superfamily of proteins engages in a pleiotropy of physiological functions associated with various diseases. C1QL proteins demonstrate important protective and regulatory roles in the endocrine, immune, cardiovascular, and nervous systems in both human and rodent studies. Studies in the central nervous system (CNS), adipose, and muscle tissue reveal several C1QL protein and receptor pathways altering multiple cellular responses, including cell fusion, morphology, and adhesion. This review examines C1QL proteins across these systems, summarizing functional and disease associations and highlighting cellular responses based on in vitro and in vivo data, receptor interaction partners, and C1QL-associated protein signaling pathways. We highlight the functions of C1QL proteins in organizing CNS synapses, regulating synapse homeostasis, maintaining excitatory synapses, and mediating signaling and trans-synaptic connections. Yet, while these associations are known, present studies provide insufficient insight into the underlying molecular mechanism of their pleiotropy, including specific protein interactions and functional pathways. Thus, we suggest several areas for more in-depth and interdisciplinary hypothesis testing.

GPX4-independent ferroptosis—a new strategy in disease’s therapy

Ferroptosis is a form of programmed cell death characterized by intracellular iron accumulation and lipid peroxidation, and earlier studies identified glutathione peroxidase 4 (GPX4) as an essential regulator of this process. Ferroptosis plays an essential role in tumors, degenerative diseases, and ischemia-reperfusion injury. However, researchers have found that inhibition of GPX4 does not entirely suppress ferroptosis in certain diseases, or cells express resistance to ferroptosis agonists that inhibit GPX4. As research progresses, it has been discovered that there are multiple regulatory pathways for ferroptosis that are independent of GPX4. The study of GPX4-independent ferroptosis pathways can better target ferroptosis to prevent and treat various diseases. Here, the currently inhibited pulmonary GPX4-dependent ferroptosis pathways will be reviewed.

A Putative Guanosine Triphosphate Cyclohydrolase I Named CaGCH1 Is Involved in Hyphal Branching and Fruiting Development in Cyclocybe aegerita

Guanosine triphosphate (GTP) cyclohydrolase I (GCH1) is the limiting enzyme of the tetrahydrobiopterin (BH4) synthesis pathway. The disruption of gch1 gene may cause conditional lethality due to folic acid auxotrophy in microorganisms, although the function of gch1 in basidiomycetes has not been deciphered so far. In the present study, gch1 expression in Cyclocybe aegerita (cagch1) was downregulated using the RNAi method, which resulted in growth retardation in both solid and liquid medium, with the hyphal tips exhibiting increased branching compared to that in the wild strain. The development of fruiting bodies in the mutant strains was significantly blocked, and there were short and bottle-shaped stipes. The transcriptional profile revealed that the genes of the MAPK pathway may be involved in the regulation of these effects caused by cagch1 knockdown, which provided an opportunity to study the role of gch1 in the development process of basidiomycetes.

AMP-activated protein kinase α1 phosphorylates PHD2 to maintain systemic iron homeostasis

BACKGROUND

Iron is essential for all mammalian life, and either a deficiency or excess of iron can cause diseases. AMP-activated protein kinase (AMPK) is a critical regulator of metabolic homeostasis; however, it has not been established whether AMPK regulates iron metabolism.

METHODS

Iron, hepcidin and ferroportin levels were examined in mice with global and hepatocyte-specific knockout of AMPKα1 and AMPKα2. Primary AMPKα1 or AMPKα2 deleted hepatocytes were isolated and cultured in hypoxia condition to explore PHD2, HIF and hydroxylated HIF1α levels. We performed immunoprecipitation, in vitro AMPK kinase assay and site-direct mutant assay to detect phosphorylation sites of PHD2. We also obtained liver tissues from patients with anaemia of chronic disease undergoing surgery, AMPKα1 and hydroxylated HIF1α levels were measured by immunohistochemical analysis.

RESULTS

We found that mice with global deficiency of AMPKα1, but not AMPKα2, exhibited hypoferraemia as well as iron sequestration in the spleen and liver. Hepatocyte-specific, but not myeloid-specific, ablation of AMPKα1 also reduced serum iron levels in association with increased hepcidin and decreased ferroportin protein levels. Mechanistically, AMPKα1 directly phosphorylated prolyl hydroxylase domain-containing (PHD)2 at serines 61 and 136, which suppressed PHD2-dependent hydroxylation of hypoxia-inducible factor (HIF)1α and subsequent regulation of hepatic hepcidin-related iron signalling. Inhibition of PHD2 hydroxylation ameliorated abnormal iron metabolism in hepatic AMPKα1-deficient mice. Furthermore, we found hepatic AMPKα/PHD2/HIFα/ hepcidin axes were highly clinically relevant to anaemia of chronic disease.

CONCLUSION

In conclusion, these observations suggest that hepatic AMPKα1 has an essential role in maintaining iron homeostasis by PHD2-dependent regulation of hepcidin, thus providing a potentially promising approach for the treatment of iron disturbances in chronic diseases.

C1q tumor necrosis factor-related protein 1: a promising therapeutic target for atherosclerosis

ABSTRACT

Atherosclerosis serves as the pathological basis of most cardiovascular and cerebrovascular diseases. C1q tumor necrosis factor-related protein (CTRP1) is a 35-kDa glycoprotein synthesized by various tissues and cells, such as adipose tissue and macrophages. As an adiponectin paralog, CTRP1 signals through adiponectin receptor 1 (AdipoR1) and participates in a variety of pathophysiological processes. Circulating CTRP1 levels are significantly increased in patients with coronary artery disease. Importantly, CTRP1 was shown to accelerate the development of atherosclerosis by promoting vascular inflammation, macrophage foam cell formation and endothelial barrier dysfunction. This review focused on recent advances regarding the role of CTRP1 in atherogenesis with an emphasis on its potential as a novel biomarker and a promising therapeutic target for atherosclerosis-related diseases.

Disturbed Lipid Metabolism in Diabetic Patients with Manifest Coronary Artery Disease Is Associated with Enhanced Inflammation

Background: Diabetic vasculopathy plays an important role in the pathophysiology of coronary artery disease (CAD) with oxidative stress as a strong mediator. This study aims to elucidate the underlying pathomechanisms of diabetic cardiac vasculopathy leading to coronary disease with an emphasis on the role of oxidative stress. Therefore, novel insights into antioxidant pathways might contribute to new strategies in the treatment and prevention of diabetic CAD. Methods: In 20 patients with insulin-dependent or non-insulin dependent diabetes mellitus (IDDM/NIDDM) and 39 non-diabetic (CTR) patients, myocardial markers of oxidative stress, vasoactive proteins, endothelial nitric oxide synthase (eNOS), activated phosphorylated eNOS (p-eNOS), and antioxidant enzymes, e.g., tetrahydrobiopterin generating dihydrofolate reductase (DHFR), heme oxygenase (HO-1), as well as serum markers of inflammation, e.g., E-selectin, interleukin-6 (IL-6), and lipid metabolism, e.g., high- and low-density lipoptrotein (HDL- and LDL-cholesterol) were determined in specimens of right atrial tissue and in blood samples from type 2 diabetic and non-diabetic patients undergoing coronary artery bypass graft (CABG) surgery. Results: IDDM/NIDDM increased markers of inflammation (e.g., E-selectin, p = 0.005 and IL-6, p = 0.051), decreased the phosphorylated myocardial p-eNOS (p = 0.032), upregulated the myocardial stress response protein HO-1 (p = 0.018), and enhanced the serum LDL-/HDL-cholesterol ratio (p = 0.019). However, the oxidative stress markers in the myocardium and the expression of vasoactive proteins (eNOS, DHFR) showed only marginal adverse changes in patients with IDDM/NIDDM. Conclusion: Dyslipidemia and myocardial inflammation seem to be the major determinants of diabetic CAD complications. Dysregulation in pro-oxidative enzymes might be attributable to the severity of CAD and oxidative stress levels in all included patients undergoing CABG.

CTRP13 Protects H9c2 Cells Against Hypoxia/Reoxygenation (H/R)-Induced Injury Via Regulating the AMPK/Nrf2/ARE Signaling Pathway

Myocardial infarction (MI) is identified as the myocardial necrosis due to myocardial ischemia/reperfusion (I/R) injury and remains a leading cause of mortality. C1q/TNF-related protein 13 (CTRP13) is a member of CTRP family that has been found to be involved in coronary artery disease (CAD). However, the role of CTRP13 in MI remains unclear. We aimed to explore the functional role of CTRP13 in H9c2 cells exposed to hypoxia/reoxygenation (H/R). Our results demonstrated that H/R stimulation significantly decreased the expression of CTRP13 in H9c2 cells. H/R-induced an increase in ROS production and reductions in activities of SOD and CAT were prevented by CTRP13 overexpression but were aggravated by CTRP13 silencing. Moreover, CTRP13 overexpression could reverse the inductive effect of H/R on caspase-3 activity and bax expression, as well as the inhibitory effect of H/R on bcl-2 expression in H9c2 cells. However, CTRP13 silencing presented opposite effects with CTRP13 overexpression. Furthermore, CTRP13 overexpression enhanced the H/R-stimulated the expression levels of p-AMPK and nuclear Nrf2, and Nrf2 transcriptional activity. However, inhibition of AMPK reversed the CTRP13-mediated activation of Nrf2/ARE signaling and the cardiac-protective effect in H/R-exposed H9c2 cells. Additionally, silencing of Nrf2 reversed the protective effects of CTRP13 against H/R-stimulated oxidative stress and apoptosis in H9c2 cells. Finally, recombinant CTRP13 protein attenuated myocardial I/R-induced injury in rats. Taken together, these findings indicated that CTRP13 protected H9c2 cells from H/R-stimulated oxidative stress and apoptosis via regulating the AMPK/Nrf2/ARE signaling pathway. Our results provided evidence for the therapeutic potential of CTRP13 in myocardial I/R injury.

Ferroptosis and Its Potential Role in Metabolic Diseases: A Curse or Revitalization?

Ferroptosis is classified as an iron-dependent form of regulated cell death (RCD) attributed to the accumulation of lipid hydroperoxides and redox imbalance. In recent years, accumulating researches have suggested that ferroptosis may play a vital role in the development of diverse metabolic diseases, for example, diabetes and its complications (e.g., diabetic nephropathy, diabetic cardiomyopathy, diabetic myocardial ischemia/reperfusion injury and atherosclerosis [AS]), metabolic bone disease and adrenal injury. However, the specific physiopathological mechanism and precise therapeutic effect is still not clear. In this review, we summarized recent advances about the development of ferroptosis, focused on its potential character as the therapeutic target in metabolic diseases, and put forward our insights on this topic, largely to offer some help to forecast further directions.

Apolipoprotein A-I mimetic peptide inhibits atherosclerosis by increasing tetrahydrobiopterin via regulation of GTP-cyclohydrolase 1 and reducing uncoupled endothelial nitric oxide synthase activity

BACKGROUND AND AIMS

The apolipoprotein A-I mimetic peptide D-4F, among its anti-atherosclerotic effects, improves vasodilation through mechanisms not fully elucidated yet.

METHODS

Low-density lipoprotein (LDL) receptor null (LDLr-/-) mice were fed Western diet with or without D-4F. We then measured atherosclerotic lesion formation, endothelial nitric oxide synthase (eNOS) phosphorylation and its association with heat shock protein 90 (HSP90), nitric oxide (NO) and superoxide anion (O2•-) production, and tetrahydrobiopterin (BH4) and GTP-cyclohydrolase 1 (GCH-1) concentration in the aorta. Human umbilical vein endothelial cells (HUVECs) and aortas were treated with oxidized LDL (oxLDL) with or without D-4F; subsequently, BH4 and GCH-1 concentration, NO and O2•- production, eNOS association with HSP90, and endothelium-dependent vasodilation were measured.

RESULTS

Unexpectedly, eNOS phosphorylation, eNOS-HSP90 association, and O2•- production were increased, whereas BH4 and GCH-1 concentration and NO production were reduced in atherosclerosis. D-4F significantly inhibited atherosclerosis, eNOS phosphorylation, eNOS-HSP90 association, and O2•- generation but increased NO production and BH4 and GCH-1 concentration. OxLDL reduced NO production and BH4 and GCH-1 concentration but enhanced O2•- generation and eNOS association with HSP90, and impaired endothelium-dependent vasodilation. D-4F inhibited the overall effects of oxLDL.

CONCLUSIONS

Hypercholesterolemia enhanced uncoupled eNOS activity by decreasing GCH-1 concentration, thereby reducing BH4 levels. D-4F reduced uncoupled eNOS activity by increasing BH4 levels through GCH-1 expression and decreasing eNOS phosphorylation and eNOS-HSP90 association. Our findings elucidate a novel mechanism by which hypercholesterolemia induces atherosclerosis and D-4F inhibits it, providing a potential therapeutic approach.

CTRP13 Mitigates Abdominal Aortic Aneurysm Formation via NAMPT1

Abdominal aortic aneurysm (AAA) is a life-threatening cardiovascular disease characterized by localized dilation of the abdominal aorta. C1q/tumor necrosis factor (TNF)-related protein-13 (CTRP13) is a secreted adipokine that plays important roles in the cardiovascular system. However, the functional role of CTRP13 in the formation and development of AAA has yet to be explored. In this study, we determined that serum CTRP13 levels were significantly downregulated in blood samples from patients with AAA and in rodent AAA models induced by Angiotensin II (Ang II) in ApoE^-/- mice or by CaCl₂ in C57BL/6J mice. Using two distinct murine models of AAA, CTRP13 was shown to effectively reduce the incidence and severity of AAA in conjunction with reduced aortic macrophage infiltration, expression of proinflammatory cytokines (interleukin-6 [IL-6], TNF-α, and monocyte chemoattractant protein 1 [MCP-1]), and vascular smooth muscle cell (SMC) apoptosis. Mechanistically, nicotinamide phosphoribosyl-transferase 1 (NAMPT1) was identified as a new target of CTRP13. The decreased in vivo and in vitro expression of NAMPT1 was markedly reversed by CTRP13 supplementation in a ubiquitination-proteasome-dependent manner. NAMPT1 knockdown further blocked the beneficial effects of CTRP13 on vascular inflammation and SMC apoptosis. Overall, our study reveals that CTRP13 management may be an effective treatment for preventing AAA formation.

E3 Ligase FBXW2 Is a New Therapeutic Target in Obesity and Atherosclerosis

Chronic low-grade inflammation orchestrated by macrophages plays a critical role in metabolic chronic diseases, like obesity and atherosclerosis. However, the underlying mechanism remains to be elucidated. Here, the E3 ubiquitin ligase F-box/WD Repeat-Containing Protein 2 (FBXW2), the substrate-binding subunit of E3 ubiquitin ligase SCF (a complex of FBXW2, SKP1, and cullin-1), as an inflammatory mediator in macrophages, is identified. Myeloid-specific FBXW2 gene deficiency improves both obesity-associated with insulin resistance and atherosclerosis in murine models. The beneficial effects by FBXW2 knockout are accompanied by decreased proinflammatory responses and macrophage infiltration in the microenvironment. Mechanistically, it is identified that KH-type splicing regulatory protein (KSRP) is a new bona fide ubiquitin substrate of SCFFBXW2. Inhibition of KSRP prevents FBXW2-deficient macrophages from exerting a protective effect on inflammatory reactions, insulin resistance and plaque formation. Furthermore, it is demonstrated that the C-terminus (P3) of FBXW2 competitively ablates the function of FBXW2 in KSRP degradation and serves as an effective inhibitor of obesity and atherogenesis progression. Thus, the data strongly suggest that SCFFBXW2 is an important mediator in the context of metabolic diseases. The development of FBXW2 (P3)-mimicking inhibitors and small-molecular drugs specifically abrogating KSRP ubiquitination-dependent inflammatory responses are viable approaches for obesity and atherosclerosis treatment.

Ionizing radiation induces BH4 deficiency by downregulating GTP-cyclohydrolase 1, a novel target for preventing and treating radiation enteritis

Radiation enteritis (RE) is a common side effect after radiotherapy for abdominal cancer. RE pathogenesis is complicated, with no drugs available for prevention or treatments. Intestinal ischemia is a key factor in the occurrence and development of enteritis. The effect of ionizing radiation (IR) on intestinal ischemia is unknown. Deficiency of tetrahydrobiopterin (BH4) produced by GTP-cyclohydrolase 1 (Gch1) is important in ischemic diseases. This study focused on the relationship of Gch1/BH4 between intestinal ischemia in radiation enteritis. BH4 levels were analyzed by high-performance liquid chromatography in humans and rats after radiotherapy. Intestinal blood perfusion was measured by laser doppler flow imaging. Vascular ring tests determined the diastolic functions of rat mesenteric arteries. Gene, protein, and immunohistochemical staining experiments and inhibitor interventions were used to investigate Gch1 and endothelial NOS (eNOS) in rat mesenteric arteries and endothelial cells. The results showed that IR decreased BH4 levels in patients and rats after radiotherapy and decreased intestinal blood perfusion in rats. The degree of change in intestinal ischemia was consistent with intestinal villus injury. Gch1 mRNA and protein levels and nitric oxide (NO) production significantly decreased, while eNOS uncoupling in arterial and vascular endothelial cells strongly increased. BH4 supplementation improved eNOS uncoupling and NO levels in vascular endothelia after IR. The results of this study showed that downregulation of Gch1 in intestinal blood vessels after IR is an important target in RE. BH4 supplementation may prevent intestinal ischemia and improve vascular endothelial function after IR. These findings have clinical significance for the prevention and treatment of RE.