RTK signaling requires C3ar1/C5ar1 and IL-6R joint signaling to repress dominant PTEN, SOCS1/3 and PHLPP restraint

Critical Role of CD55 in Controlling Wound Healing

How reparative processes are coordinated following injury is incompletely understood. In recent studies, we showed that autocrine C3a and C5a receptor (C3ar1 and C5ar1) G protein-coupled receptor signaling plays an obligate role in vascular endothelial growth factor receptor 2 growth signaling in vascular endothelial cells. We documented the same interconnection for platelet-derived growth factor receptor growth signaling in smooth muscle cells, epidermal growth factor receptor growth signaling in epidermal cells, and fibroblast growth factor receptor signaling in fibroblasts, indicative of a generalized cell growth regulatory mechanism. In this study, we examined one physiological consequence of this signaling circuit. We found that disabling CD55 (also known as decay accelerating factor), which lifts restraint on autocrine C3ar1/C5ar1 signaling, concomitantly augments the growth of each cell type. The mechanism is heightened C3ar1/C5ar1 signaling resulting from the loss of CD55's restraint jointly potentiating growth factor production by each cell type. Examination of the effect of lifted CD55 restraint in four types of injury (burn, corneal denudation, ear lobe puncture, and reengraftment of autologous skin) showed that disabled CD55 function robustly accelerated healing in all cases, whereas disabled C3ar1/C5ar1 signaling universally retarded it. In wild-type mice with burns or injured corneas, applying a mouse anti-mouse CD55 blocking Ab (against CD55's active site) to wounds accelerated the healing rate by 40-70%. To our knowledge, these results provide new insights into mechanisms that underlie wound repair and open up a new tool for accelerating healing.

KLF4 and CD55 expression and function depend on each other

The transcription factor Kruppel-like factor 4 (KLF4) regulates the expression of immunosuppressive and anti-thrombotic proteins. Despite its importance in maintaining homeostasis, the signals that control its expression and the mechanism of its transactivation remain unclarified. CD55 [aka decay accelerating factor (DAF)], now known to be a regulator of T and B cell responses, biases between pro- and anti-inflammatory processes by controlling autocrine C3a and C5a receptor (C3ar1/C5ar1) signaling in cells. The similarity in CD55's and KLF4's regulatory effects prompted analyses of their functional relationship. In vascular endothelial cells (ECs), CD55 upregulation accompanied KLF4 expression via a p-CREB and CREB Binding Protein (CBP) mechanism. In both ECs and macrophages, CD55 expression was essential for KLF4's downregulation of pro-inflammatory/pro-coagulant proteins and upregulation of homeostatic proteins. Mechanistic studies showed that upregulation of KLF4 upregulated CD55. The upregulated CD55 in turn enabled the recruitment of p-CREB and CBP to KLF4 needed for its transcription. Activation of adenylyl cyclase resulting from repression of autocrine C3ar1/C5ar1 signaling by upregulated CD55 concurrently led to p-CREB and CBP recruitment to KLF4-regulated genes, thereby conferring KLF4's transactivation. Accordingly, silencing CD55 in statin-treated HUVEC disabled CBP transfer from the E-selectin to the eNOS promoter. Importantly, silencing CD55 downregulated KLF4's expression. It did the same in untreated HUVEC transitioning from KLF4low growth to KLF4hi contact inhibition. KLF4's and CD55's function in ECs and macrophages thus are linked via a novel mechanism of gene transactivation. Because the two proteins are co-expressed in many cell types, CD55's activity may be broadly tied to KLF4's immunosuppressive and antithrombotic activities.

Disabled C3ar1/C5ar1 Signaling in Foxp3+ T Regulatory Cells Leads to TSDR Demethylation and Long-Term Stability

Demethylation of the T regulatory cell (Treg)-specific demethylation region (TSDR) of the Foxp3 gene is the hallmark of Foxp3+ Treg stability, but the cellular signaling that programs this epigenetic state remains undefined. In this article, we show that suppressed C3a and C5a receptor (C3ar1/C5ar1) signaling in murine Tregs plays an obligate role. Murine C3ar1-/-C5ar1-/- Foxp3+ cells showed increased suppressor of cytokine signaling 1/2/3 expression, vitamin C stabilization, and ten-eleven translocation (TET) 1, TET2, and TET3 expression, all of which are linked to Treg stability. C3ar1-/-C5ar1-/- Foxp3+ cells additionally were devoid of BRD4 signaling that primes Th17 cell lineage commitment. Orally induced OVA-specific C3ar1-/-C5ar1-/- Foxp3+ OT-II Tregs transferred to OVA-immunized wild-type recipients remained >90% Foxp3+ out to 4 mo, whereas identically generated CD55-/- (DAF-/-) Foxp3+ OT-II Tregs (in which C3ar1/C5ar1 signaling is potentiated) lost >75% of Foxp3 expression by 14 d. After 4 mo in vivo, the C3ar1-/-C5ar1-/- Foxp3+ OT-II Tregs fully retained Foxp3 expression even with OVA challenge and produced copious TGF-β and IL-10. Their TSDR was demethylated comparably with that of thymic Tregs. They exhibited nuclear translocation of NFAT and NF-κB reported to stabilize thymic Tregs by inducing hairpin looping of the TSDR to the Foxp3 promoter. Thus, disabled CD4+ cell C3ar1/C5ar1 signaling triggers the sequential cellular events that lead to demethylation of the Foxp3 TSDR.

The effect of butylphthalide on improving the neurological function of patients with acute anterior circulation cerebral infarction after mechanical thrombectomy

Butylphthalide can improve blood circulation in patients with acute cerebral infarction. Complement 3a receptor 1 (C3aR1) is involved in the regulation of innate immune response and pathogen monitoring, which is closely related to the pathophysiological processes of breast cancer, neurogenesis and lipid catabolism. Our study explored the therapeutic effect of butylphthalide on improving the neurological function of patients with acute anterior circulation cerebral infarction after mechanical thrombectomy, and evaluated the correlation between serum C3aR1 and butylphthalide on improving the neurological function after mechanical thrombectomy. 288 patients with acute anterior circulation cerebral infarction who were admitted to our hospital from January 2019 to November 2022 and were treated with mechanical thrombectomy for the first time were included in this retrospective study and divided into the butylphthalide group and control group that they received treatment methods. The National Institutes of Health Stroke Scale (NIHSS) scale was used to evaluate the patient neurological function treatment efficacy, and the modified Rankin Scale (mRS) scale was used to measure the patient neurological function status 3 months after surgery. Enzyme-linked immunosorbent assay method was used to determine the content of C3aR1 in serum. Two weeks after thrombus removal, the NIHSS efficacy of the butylphthalide group and the control group were 94.44% and 72.22%, respectively. The butylphthalide group was significantly higher than the control group (P < .001). Three months after the operation, the mRS score of the butylphthalide group was significantly lower than that of the control group (P = .001), and the excellent and good rate was significantly higher than that of the control group (P < .001). The serum C3aR1 level of the butylphthalide group was significantly lower than that of the control group 2 weeks after operation and 3 months after operation (P < .001). The serum C3aR1 was positively correlated with the efficacy of NIHSS (R = 0.815, P = .004), which was positively correlated with mRS score (R = 0.774, P = .007). Butylphthalide can improve the therapeutic effect of neurological function in patients with acute anterior circulation cerebral infarction after mechanical thrombus removal. The patient serum C3aR1 is related to the patient neurotherapy efficacy and neurological function status, and its level can reflect the patient neurological function recovery to a certain extent.

Vascular Endothelial Cells Produce Coagulation Factors That Control Their Growth via Joint Protease-Activated Receptor and C5a Receptor 1 (CD88) Signaling

As per the classical view of the coagulation system, it functions solely in plasma to maintain hemostasis. An experimental approach modeling vascular reconstitution was used to show that vascular endothelial cells (ECs) endogenously synthesize coagulation factors during angiogenesis. Intracellular thrombin generated from this synthesis promotes the mitotic function of vascular endothelial cell growth factor A (VEGF-A). The thrombin concurrently cleaves C5a from EC-synthesized complement component C5 and unmasks the tethered ligand for EC-expressed protease-activated receptor 4 (PAR4). The two ligands jointly trigger EC C5a receptor-1 (C5ar1) and PAR4 signaling, which together promote VEGF receptor 2 growth signaling. C5ar1 is functionally associated with PAR4, enabling C5a or thrombin to elicit Gαi and/or Gαq signaling. EC coagulation factor and EC complement component synthesis concurrently down-regulate with contact inhibition. The connection of these processes with VEGF receptor 2 signaling provides new insights into mechanisms underlying angiogenesis. Knowledge of endogenous coagulation factor/complement component synthesis and joint PAR4/C5ar1 signaling could be applied to other cell types.

Analyzing the impact of ATF3 in tumorigenesis and immune cell infiltration of ovarian tumor: a bioinformatics study

ATF3 is an essential transcription activator in regulating cancer-related genetic expression. To identify the role of ATF3 in ovarian tumor, we investigated the correlation between ATF3 expression and the clinicopathological properties using multiple database. The cBioPortal and GEPIA database displayed the clinical information of ovarian patients harboring or without harboring ATF3 mutation. Furthermore, we assessed the relationship between survival and ATF3 expression level using Kaplan-Meier plotter, which reveals that the ovarian patients with higher expression of ATF3 suffered the worse overall survival and progression-free survival. The differentially expressed genes were analyzed using gene ontology, protein-protein interaction network, and gene set enrichment analysis to identify the hub gene and critical pathways, significantly affecting the tumorigenesis of ovarian tumor. Finally, we assessed the correlation between ATF3 and immune cell infiltration using Tumor Immunoassay Resource (TIMER) database. The results demonstrated that higher expression has a positive correlation with macrophage infiltration, expression for M1- and M2-type macrophages. Our study suggests that ATF3 can regulate the cell cycle and heme-related oxidative phosphorylation process, and it may be a critical factor to regulate the macrophage cell to be infiltrated into ovarian cancer. ATF3 can be used as a biomarker for diagnosis and therapy of ovarian tumor.

Mitochondrial C3a Receptor Activation in Oxidatively Stressed Epithelial Cells Reduces Mitochondrial Respiration and Metabolism

Complement component 3 fragment C3a is an anaphylatoxin involved in promoting cellular responses important in immune response and host defense. Its receptor (C3a receptor, C3aR) is distributed on the plasma membrane; however, lysosomal localization in immune cells has been reported. Oxidative stress increases intracellular reactive oxygen species (ROS), and ROS activate complement signaling in immune cells and metabolic reprogramming. Here we tested oxidative stress and intracellular complement in mitochondrial dysfunction in RPE cells using high resolution live-cell imaging, and metabolism analysis in isolated mitochondria using Seahorse technology. While C3aR levels were unaffected by oxidative stress, its cell membrane levels decreased and mitochondrial (mt) localization increased. Trafficking was dependent on endocytosis, utilizing endosomal-to-mitochondrial cargo transfer. H₂O₂-treatment also increased C3a-mtC3aR co-localization dose-dependently. In isolated mitochondria from H₂O₂-treated cells C3a increased mitochondrial Ca²⁺ uptake, that could be inhibited by C3aR antagonism (SB290157), mitochondrial Ca²⁺ uniporter blocker (Ru360), and Gαi-protein inhibition (pertussis toxin, PTX); and inhibited mitochondrial repiration in an SB290157- and PTX-dependent manner. Specifically, mtC3aR activation inhibited state III ADP-driven respiration and maximal respiratory capacity. Mitochondria from control cells did not respond to C3a. Furthermore, transmitochondrial cybrid ARPE-19 cells harboring J haplogroup mitochondria that confer risk for age-related macular degeneration, showed high levels of mtC3aR and reduced ATP production upon C3a stimulation. Our findings suggest that oxidative stress increases mtC3aR, leading to altered mitochondrial calcium uptake and ATP production. These studies will have important implication in our understanding on the balance of extra- and intracellular complement signaling in controlling cellular health and dysfunction.