The matricellular "cysteine-rich protein 61" is released from activated platelets and increased in the circulation during experimentally induced sepsis

Analysis of CCN Functions in Liver Regeneration After Partial Hepatectomy

The remarkable regenerative capability of the liver has long been appreciated. Upon significant loss of liver tissue, the remnant liver can grow rapidly to restore the original liver mass through a combination of hepatocyte proliferation and hypertrophy to maintain homeostasis. Experimentally, 2/3 partial hepatectomy in mice has been used extensively as a model to dissect the molecular mechanism of liver regeneration and the genetic networks involved. Herein, we describe the protocols for partial hepatectomy and analyses of pertinent CCN protein functions.

Cellular communication network factor 1-stimulated liver macrophage efferocytosis drives hepatic stellate cell activation and liver fibrosis

Following inflammatory injury in the liver, neutrophils quickly infiltrate the injured tissue to defend against microbes and initiate the repair process; these neutrophils are short lived and rapidly undergo apoptosis. Hepatic stellate cells (HSCs) are the principal precursor cells that transdifferentiate into myofibroblast-like cells, which produce a large amount of extracellular matrix that promotes repair but can also lead to fibrosis if the injury becomes chronic. The matricellular protein cellular communication network factor 1 (CCN1) acts as a bridging molecule by binding phosphatidylserine in apoptotic cells and integrin α_v β₃ in phagocytes, thereby triggering efferocytosis or phagocytic clearance of the apoptotic cells. Here, we show that CCN1 induces liver macrophage efferocytosis of apoptotic neutrophils in carbon tetrachloride (CCl₄ )-induced liver injury, leading to the production of activated transforming growth factor (TGF)-β1, which in turn induces HSC transdifferentiation into myofibroblast-like cells that promote fibrosis development. Consequently, knock-in mice expressing a single amino acid substitution in CCN1 rendering it unable to bind α_v β₃ or induce efferocytosis are impaired in neutrophil clearance, production of activated TGF-β1, and HSC transdifferentiation, resulting in greatly diminished liver fibrosis following exposure to CCl₄ . Conclusion: These results reveal the crucial role of CCN1 in stimulating liver macrophage clearance of apoptotic neutrophils, a process that drives HSC transdifferentiation into myofibroblastic cells and underlies fibrogenesis in chronic liver injury.

Senescent hepatic stellate cells promote liver regeneration through IL-6 and ligands of CXCR2

Senescent cells have long been associated with deleterious effects in aging-related pathologies, although recent studies have uncovered their beneficial roles in certain contexts, such as wound healing. We have found that hepatic stellate cells (HSCs) underwent senescence within 2 days after 2/3 partial hepatectomy (PHx) in young (2–3 months old) mice, and the elimination of these senescent cells by using the senolytic drug ABT263 or by using a genetic mouse model impaired liver regeneration. Senescent HSCs secrete IL-6 and CXCR2 ligands as part of the senescence-associated secretory phenotype, which induces multiple signaling pathways to stimulate liver regeneration. IL-6 activates STAT3, induces Yes-associated protein (YAP) activation through SRC family kinases, and synergizes with CXCL2 to activate ERK1/2 to stimulate hepatocyte proliferation. The administration of either IL-6 or CXCL2 partially restored liver regeneration in mice with senescent cell elimination, and the combination of both fully restored liver weight recovery. Furthermore, the matricellular protein central communication network factor 1 (CCN1, previously called CYR61) was rapidly elevated in response to PHx and induced HSC senescence. Knockin mice expressing a mutant CCN1 unable to bind integrin α₆β₁ were deficient in senescent cells and liver regeneration after PHx. Thus, HSC senescence, largely induced by CCN1, is a programmed response to PHx and plays a critical role in liver regeneration through signaling pathways activated by IL-6 and ligands of CXCR2.

Association of serum Cyr61 levels with peripheral arterial disease in subjects with type 2 diabetes

Background

The prevalence of peripheral artery disease (PAD) is obviously increased in patients with diabetes. Existing evidence shows that cysteine-rich angiogenic inducer 61 (Cyr61), a 40-kD secreted protein, plays important roles in regulating cellular physiological processes. Recent studies have demonstrated a significant correlation between serum Cyr61 and atherosclerosis. However, the relationship between Cyr61 levels and PAD in patients with type 2 diabetes (T2DM) remains obscure.

Methods

Data from a total of 306 subjects with T2DM were cross-sectionally analysed. The extent of PAD was determined by using the Fontaine classification, which defines four stages. We measured serum Cyr61 concentrations by ELISA in subjects with and without PAD at Fontaine’s stage II, III, or IV. Logistic regression models were used to examine the independent association of Cyr61 with PAD.

Results

Out of the 306 subjects enrolled, 150 were free from PAD, while 156 had clinically significant PAD. In subjects with PAD, the prevalences of Fontaine classification stages II, III and IV were 48.7%, 32.1%, and 19.2%, respectively. Patients with more advanced PAD had significantly higher Cyr61 (P for trend < 0.001). The prevalence of PAD on the basis of severity increased with increasing Cyr61 quartiles (all P values for trends < 0.001), and the severity of PAD was positively correlated with Cyr61 quartiles (r = 0.227, P = 0.006). The association of Cyr61 levels with PAD remained after adjusting for major risk factors in a logistic regression analysis.

Conclusions

Our results demonstrated that Cyr61 was significantly increased in PAD patients with T2DM and that Cyr61 levels were positively associated with disease severity. Cyr61 could be a promising biomarker and further studies are needed to assess its clinical utility.

CCN1 is an opsonin for bacterial clearance and a direct activator of Toll-like receptor signaling

Expression of the matricellular protein CCN1 (CYR61) is associated with inflammation and is required for successful wound repair. Here, we show that CCN1 binds bacterial pathogen-associated molecular patterns including peptidoglycans of Gram-positive bacteria and lipopolysaccharides of Gram-negative bacteria. CCN1 opsonizes methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa and accelerates their removal by phagocytosis and increased production of bactericidal reactive oxygen species in macrophages through the engagement of integrin α_vβ₃. Mice with myeloid-specific Ccn1 deletion and knock-in mice expressing CCN1 unable to bind α_vβ₃ are more susceptible to infection by S. aureus or P. aeruginosa, resulting in increased mortality and organ colonization. Furthermore, CCN1 binds directly to TLR2 and TLR4 to activate MyD88-dependent signaling, cytokine expression and neutrophil mobilization. CCN1 is therefore a pattern recognition receptor that opsonizes bacteria for clearance and functions as a damage-associated molecular pattern to activate inflammatory responses, activities that contribute to wound healing and tissue repair.

CCN1 is a matricellular protein with a variety of functions, including an effect on wound healing and an association with inflammation. Here, the authors identify a possible mechanism by showing that CCN1 mediates the clearance of bacterial infections in mice and activates TLR signalling.

Evaluation of serum cysteine-rich protein 61 levels in patients with coronary artery disease

AIM

The aim is to evaluate serum cysteine-rich protein 61 (Cyr61) levels in patients with coronary artery disease (CAD).

PATIENTS & METHODS

Serum Cyr61 levels were measured in 180 patients with CAD and 74 participants without CAD.

RESULTS

Serum Cyr61 levels were significantly higher in CAD patients. Patients with acute coronary syndrome showed significantly higher Cyr61 than those with stable angina pectoris. Serum Cyr61 levels in complex lesion group were significantly higher. Serum Cyr61 was positively correlated with Gensini score and C-reactive protein. Multivariable logistic regression analyses demonstrated that serum Cyr61 levels were independently correlated with the existence of CAD (p = 0.01).

CONCLUSION

Our study suggested Cyr61 as a potential biomarker in characterizing CAD and therapeutic target for CAD.

Toll-like receptors elicit different recruitment kinetics of monocytes and neutrophils in mouse acute inflammation

Leukocyte recruitment is an important process in combating pathogens. The largest class of circulating leukocytes are neutrophils, which rapidly invade inflamed tissue, followed by inflammatory Ly6C⁺ monocytes. Ly6C^low monocytes patrol the endothelial wall routinely in the steady state. We recently reported early luminal recruitment of Ly6C^low monocytes, which preceded and orchestrated neutrophil arrival and extravasation in response to TLR7/8-mediated vascular inflammation. Here we dissected the kinetics of recruitment of monocytes and neutrophils and examined the dynamics of Ly6C^low monocytes in response to several other Toll-like receptor (TLR) agonists, using intravital confocal microscopy. We observed two types of kinetics in mesenteric veins. TLR2, TLR5 and TLR9 agonists caused early monocyte and neutrophil influx whereas TLR3 and TLR4 agonists rapidly recruited neutrophils and caused Ly6C^low monocytes to arrive at low levels later on. All TLR agonists, except TLR9, led Ly6C^low monocytes to meticulously patrol the vascular wall. Finally, these monocytes released pro-inflammatory cytokines and chemokines implicated in neutrophil recruitment in response to TLR2, TLR4, and TLR9 stimulation but not to TLR3 and TLR5 agonists. These results refine our understanding of the early events in the leukocyte recruitment cascade, including the patrolling behavior of Ly6C^low monocytes, in TLR-mediated acute vascular inflammation.

CCN1/CYR61-mediated meticulous patrolling by Ly6Clow monocytes fuels vascular inflammation

Inflammation is characterized by the recruitment of leukocytes from the bloodstream. The rapid arrival of neutrophils is followed by a wave of inflammatory lymphocyte antigen 6 complex (Ly6C)-positive monocytes. In contrast Ly6C(low) monocytes survey the endothelium in the steady state, but their role in inflammation is still unclear. Here, using confocal intravital microscopy, we show that upon Toll-like receptor 7/8 (TLR7/8)-mediated inflammation of mesenteric veins, platelet activation drives the rapid mobilization of Ly6C(low) monocytes to the luminal side of the endothelium. After repeatedly interacting with platelets, Ly6C(low) monocytes commit to a meticulous patrolling of the endothelial wall and orchestrate the subsequent arrival and extravasation of neutrophils through the production of proinflammatory cytokines and chemokines. At a molecular level, we show that cysteine-rich protein 61 (CYR61)/CYR61 connective tissue growth factor nephroblastoma overexpressed 1 (CCN1) protein is released by activated platelets and enables the recruitment of Ly6C(low) monocytes upon vascular inflammation. In addition endothelium-bound CCN1 sustains the adequate patrolling of Ly6C(low) monocytes both in the steady state and under inflammatory conditions. Blocking CCN1 or platelets with specific antibodies impaired the early arrival of Ly6C(low) monocytes and abolished the recruitment of neutrophils. These results refine the leukocyte recruitment cascade model by introducing endothelium-bound CCN1 as an inflammation mediator and by demonstrating a role for platelets and patrolling Ly6C(low) monocytes in acute vascular inflammation.

Regulation of CCN1 (Cyr61) in a porcine model of intestinal ischemia/reperfusion

Intestinal ischemia is a serious condition that may lead to both local and systemic inflammatory responses. Restoration of blood supply (reperfusion) to ischemic tissues often increases the extent of the tissue injury. Cysteine-rich angiogenic inducer 61 (Cyr61)/CCN1 is an extracellular matrix-associated signaling protein that has diverse functions. CCN1 is highly expressed at sites of inflammation and wound repair, and may modify cell responses. This study aimed to investigate regulation and cellular distribution of CCN1 in intestinal ischemia/reperfusion (I/R) injury in pigs. After intestinal I/R, increased expression of CCN1 was detected by quantitative RT-PCR, Western blot analysis and immunohistochemistry compared with non-ischemic intestine. Immunoflorescence staining revealed that CCN1 was mainly up-regulated in intestinal mucosa after intestinal I/R. Microvillus epithelial cells and vascular endothelial cells were strongly positive for CCN1 in intestinal I/R, while natural killer cells and/or subsets of neutrophils were only modestly positive for CCN1. Furthermore, blood samples taken from the portal and caval veins during ischemia and after reperfusion showed no change of the CCN1 levels, indicating that CCN1 was locally regulated. In conclusion, these observations show, for the first time, that the CCN1 molecule is up-regulated in response to intestinal I/R in a local manner.