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As a central molecule in complement system (CS), complement (C) 3 is upregulated in the patients and animal models of Alzheimer's disease (AD). C3 will metabolize to iC3b and C3a. iC3b is responsible for clearing ß-amyloid protein (Aß). In this scenario, C3 exerts neuroprotective effects against the disease via iC3b. However, C3a will inhibit microglia to clear the Aß, leading to the deposition of Aß and impair the functions of synapses. To their effects on AD, activation of C3a and C3a receptor (C3aR) will impair the mitochondria, leading to the release of reactive oxygen species (ROS), which activates the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasomes. The overloading of NLRP3 inflammasomes activate microglia, leading to the formation of inflammatory environment. The inflammatory environment will facilitate the deposition of Aß and abnormal synapse pruning, which results in the progression of AD. Therefore, the current review will decipher the mechanisms of C3a inducing the synapse loss via C3aR in mitochondria-dependent NLRP3 activating mechanisms, which facilitates the understanding the AD.

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OBJECTIVES: To investigate the clinical value of complement-3a receptor 1 (C3aR1) and neutrophil extracellular traps (NETs) in predicting sepsis-induced coagulopathy (SIC). METHODS: A prospective study was conducted among 78 children with sepsis who attended Xuzhou Children's Hospital Affiliated to Xuzhou Medical University from June 2022 to June 2023. According to the presence or absence of SIC, they were divided into two groups: SIC (n=36) and non-SIC (n=42) . The two groups were compared in terms of clinical data and the levels of C3aR1 and NETs. The factors associated with the occurrence of SIC were analyzed. The receiver operating characteristic (ROC) curve was used to evaluate the performance of C3aR1 and NETs in predicting SIC. RESULTS: Compared with the non-SIC group, the SIC group had significantly higher levels of C-reactive protein, interleukin-6 (IL-6), interleukin-10, C3aR1, and NETs (P<0.05). The multivaiate logistic regression analysis showed that the increases in C3aR1, NETs, and IL-6 were closely associated with the occurrence of SIC (P<0.05). The ROC curve analysis showed that C3aR1 combined with NETs had an area under the curve (AUC) of 0.913 in predicting SIC (P<0.05), which was significantly higher than the AUC of C3aR1 or IL-6 (P<0.05), while there was no significant difference in AUC between C3aR1 combined with NETs and NETs alone (P>0.05). CONCLUSIONS: There are significant increases in the expression levels of C3aR1 and NETs in the peripheral blood of children with SIC, and the expression levels of C3aR1 and NETs have a high clinical value in predicting SIC.

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PURPOSE: The complement system is considered to play an important role in the progression of myopia, whereas the influence of complement activation on the human scleral fibroblasts (HSFs) remains unknown. Hence, the effect of complement 3a (C3a) on HSFs was investigated in this study. METHODS: HSFs were cultured with exogenous C3a at 0.1 µM for various periods following different measurement protocols, and cells without C3a treatment served as negative control (NC). Cell viability was investigated using the MTS assay after 3 days of C3a treatment. Cell proliferation was evaluated by the 5-Ethynyl-20-Deoxyuridine (EdU) assay following C3a stimulation for 24 hours. Apoptosis was assessed by Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) double staining following C3a stimulation for 48 hours and the stained cells were analysed using flow cytometry. The levels of type I collagen and matrix metalloproteinase-2 (MMP-2) were analysed using ELISA following C3a stimulation for 36 and 60 hours. The level of CD59 were analysed using western blot following C3a stimulation for 60 hours. RESULTS: The MTS assay revealed that cell viability was attenuated by 13% and 8% after C3a for 2 and 3 days, respectively (P < 0.05). The EdU assay demonstrated a 9% decrease in proliferation rate for the C3a-treated cells after 24 hours (P < 0.05). The apoptosis analysis revealed an increased percentage of cells in early apoptosis (P = 0.02) and total apoptosis (P = 0.02) in the C3a-treated group. Compared with NC group, the level of MMP-2 was increased by 17.6% (P = 0.002), whereas the levels of type I collagen and CD59 were respectively decreased by 12.5% (P = 0.024) and 21.6% (P = 0.044) with C3a treatment for 60 hours. CONCLUSIONS: These results indicated that C3a-induced complement activation is potentially involved in inducing myopic-associated scleral extracellular matrix remodelling via mediating the proliferation and function of HSFs.

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OBJECTIVES@#To investigate the clinical value of complement-3a receptor 1 (C3aR1) and neutrophil extracellular traps (NETs) in predicting sepsis-induced coagulopathy (SIC).@*METHODS@#A prospective study was conducted among 78 children with sepsis who attended Xuzhou Children's Hospital Affiliated to Xuzhou Medical University from June 2022 to June 2023. According to the presence or absence of SIC, they were divided into two groups: SIC (n=36) and non-SIC (n=42) . The two groups were compared in terms of clinical data and the levels of C3aR1 and NETs. The factors associated with the occurrence of SIC were analyzed. The receiver operating characteristic (ROC) curve was used to evaluate the performance of C3aR1 and NETs in predicting SIC.@*RESULTS@#Compared with the non-SIC group, the SIC group had significantly higher levels of C-reactive protein, interleukin-6 (IL-6), interleukin-10, C3aR1, and NETs (P<0.05). The multivaiate logistic regression analysis showed that the increases in C3aR1, NETs, and IL-6 were closely associated with the occurrence of SIC (P<0.05). The ROC curve analysis showed that C3aR1 combined with NETs had an area under the curve (AUC) of 0.913 in predicting SIC (P<0.05), which was significantly higher than the AUC of C3aR1 or IL-6 (P<0.05), while there was no significant difference in AUC between C3aR1 combined with NETs and NETs alone (P>0.05).@*CONCLUSIONS@#There are significant increases in the expression levels of C3aR1 and NETs in the peripheral blood of children with SIC, and the expression levels of C3aR1 and NETs have a high clinical value in predicting SIC.

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Neurodegenerative disease is a kind of degenerative diseases of the central nervous system that seriously endanger human health. The complement 3 (C3)-complement 3a receptor (C3aR) pathway is one of the important pathways for classical complement cascade activation. A large number of studies have shown that the C3-C3aR pathway can mediate and regulate the interaction of astrocyte-microglia axis in neurons, resulting in function changes in central nervous system. In addition, studies in recent years have found that the C3-C3aR pathway is closely related to the occurrence and progress of neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, stroke, and epilepsy. This article reviews the progress of C3-C3aR pathway and discuss the role of C3-C3aR pathway in several important neurodegenerative diseases, and it provides a new idea fo treatment of these diseases.

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BACKGROUND: ABO blood group antigens in the liver are expressed mainly on endothelial cells or biliary epithelial cells but not on hepatocytes. This suggests that ABO-incompatible hepatocyte transplantation (ABOi-HTx) is theoretically feasible. However, the effects of stress on ABO blood group antigen expression caused by isolation and intraportal infusion require thorough investigation before ABOi-HTx can be implemented in clinical settings. METHODS: Human hepatocytes were isolated from liver tissue obtained from liver resection or deceased donor livers. The expression of blood group antigens on cryopreserved human liver tissues and isolated hepatocyte smear specimens were examined by immunofluorescent staining. The effect of proinflammatory cytokines on blood group antigen expression of hepatocytes was evaluated by flow cytometry. Instant blood-mediated inflammatory reaction after hepatocyte incubation with ABO-incompatible whole blood was examined using the tubing loop model. RESULTS: Blood group antigens were mainly expressed on vessels in the portal area. In hepatocyte smear specimens, isolated hepatocytes did not express blood group antigens. In contrast, a subset of cells in the smear specimens of nonparenchymal liver cells stained positive. In the flow cytometry analysis, isolated hepatocytes were negative for blood group antigens, even after 4-h incubation with cytokines. Platelet counts and complement activation were not significantly different in ABO-identical versus ABO-incompatible settings in the tubing loop model. CONCLUSION: Our study showed that blood group antigens were not expressed on hepatocytes, even after isolation procedures or subsequent incubation with cytokines. This finding is an important step toward removing the restriction of ABO matching in hepatocyte transplantation. Our results suggest that ABOi-HTx is a feasible therapeutic option, especially in patients who require urgent treatment with freshly isolated hepatocytes, such as those with acute liver failure.

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Neuroinflammation is thought to play a pivotal role in the pathogenesis of periventricular white matter (PWM) damage (PWMD) induced by neonatal sepsis. Because the complement cascade is implicated in inflammatory response, this study was carried out to determine whether C3a is involved in PWMD, and, if so, whether it would induce axonal hypomyelination. Furthermore, we explored if C3a would act through its C3a receptor (C3aR) and thence inhibit maturation of oligodendrocyte precursor cells (OPCs) via the WNT/ß-catenin signal pathway. Sprague Dawley (SD) rats aged 1 day were intraperitoneally injected with lipopolysaccharide (LPS) (1 mg/kg). C3a was upregulated in activated microglia and astrocytes in the PWM up to 7 days after LPS injection. Concomitantly, enhanced C3aR expression was observed in NG2+ oligodendrocytes (OLs). Myelin proteins including CNPase, PLP, MBP and MAG were significantly reduced in the PWM of 28-day septic rats. The number of PLP+ and MBP+ cells was markedly decreased. By electron microscopy, myelin sheath thickness was thinner and the average g-ratios were higher. This was coupled with an increase in number of NG2+ cells and decreased number of CC1+ cells. Olig1, Olig2 and SOX10 protein expression was significantly reduced in the PWM after LPS injection. Very strikingly, C3aRa administration for the first 7 days could reverse the above-mentioned pathological alterations in the PWM of septic rats. When incubated with C3a, expression of MBP, CNPase, PLP, MAG, Olig1, Olig2, SOX10 and CC1 in primary cultured OPCs was significantly downregulated as opposed to increased NG2. Moreover, WNT/ß-catenin signaling pathway was found to be implicated in inhibition of OPCs maturation and differentiation induced by C3a in vitro. As a corollary, it is speculated that C3a in the PWM of septic rats is closely associated with the disorder of OPCs differentiation and maturation through WNT/ß-catenin signaling pathway, which would contribute ultimately to axonal hypomyelination.

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TLQP-21 is a multifunctional neuropeptide and a promising new medicinal target for cardiometabolic and neurological diseases. However, to date its clearance kinetics and plasma stability have not been studied. The presence of four arginine residues led us to hypothesize that its half-life is relatively short. Conversely, its biological activities led us to hypothesize that the peptide is still taken up by adipose tissues effectively. [125I]TLQP-21 was i.v. administered in rats followed by chasing the plasma radioactivity and assessing tissue uptake. Plasma stability was measured using LC-MS. In vivo lipolysis was assessed by the palmitate rate of appearance. RESULTS: A small single i.v. dose of [125I]TLQP-21 had a terminal half-life of 110 min with a terminal clearance rate constant, kt, of 0.0063/min, and an initial half-life of 0.97 min with an initial clearance rate constant, ki, of 0.71/min. The total net uptake by adipose tissue accounts for 4.4% of the entire dose equivalent while the liver, pancreas and adrenal gland showed higher uptake. Uptake by the brain was negligible, suggesting that i.v.-injected peptide does not cross the blood-brain-barrier. TLQP-21 sustained isoproterenol-stimulated lipolysis in vivo. Finally, TLQP-21 was rapidly degraded producing several N-terminal and central sequence fragments after 10 and 60 min in plasma in vitro. This study investigated the clearance and stability of TLQP-21 peptide for the first time. While its pro-lipolytic effect supports and extends previous findings, its short half-life and sequential cleavage in the plasma suggest strategies for chemical modifications in order to enhance its stability and therapeutic efficacy.

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OBJECTIVES: Obesity is characterized by excessive fat mass and is associated with serious diseases such as type 2 diabetes. Targeting excess fat mass by sustained lipolysis has been a major challenge for anti-obesity therapies due to unwanted side effects. TLQP-21, a neuropeptide encoded by the pro-peptide VGF (non-acronymic), that binds the complement 3a receptor 1 (C3aR1) on the adipocyte membrane, is emerging as a novel modulator of adipocyte functions and a potential target for obesity-associated diseases. The molecular mechanism is still largely uncharacterized. METHODS: We used a combination of pharmacological and genetic gain and loss of function approaches. 3T3-L1 and mature murine adipocytes were used for in vitro experiments. Chronic in vivo experiments were conducted on diet-induced obese wild type, ß1, ß2, ß3-adrenergic receptor (AR) deficient and C3aR1 knockout mice. Acute in vivo lipolysis experiments were conducted on Sprague Dawley rats. RESULTS: We demonstrated that TLQP-21 does not possess lipolytic properties per se. Rather, it enhances ß-AR activation-induced lipolysis by a mechanism requiring Ca2+ mobilization and ERK activation of Hormone Sensitive Lipase (HSL). TLQP-21 acutely potentiated isoproterenol-induced lipolysis in vivo. Finally, chronic peripheral TLQP-21 treatment decreases body weight and fat mass in diet induced obese mice by a mechanism involving ß-adrenergic and C3a receptor activation without associated adverse metabolic effects. CONCLUSIONS: In conclusion, our data identify an alternative pathway modulating lipolysis that could be targeted to diminish fat mass in obesity without the side effects typically observed when using potent pro-lipolytic molecules.

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Objective To investigate the effects of erythropoietin (EPO) on complement 3a (C3a)-induced renal tubular epithelial to mesenchymal transition. Methods The HK-2 cells were divided into 6 groups namely control group,EPO group,TGF-β group,TGF-β+EPO group,C3a group and EPO+C3a group.The mRNA and protein expressions of α-SMA,E-cadherin and C3 were investigated by RT-PCR,Western blot and immunofluorescence respectively. Results Compared with control group and EPO group,the mRNA and protein expressions of α-SMA in HK-2 cells were up-regulated after the intervention of C3a or TGF-β (all P＜0.05).On the contrast,the mRNA and protein expressions of E-cadherin were down-regulated(P＜0.05),the mRNA and protein expressions of C3 were enhanced (all P＜0.05).However,all those above effects of C3a or TGF-β were inhibited after the intervention of EPO (all P＜0.05). Conclusion EPO is capable of suppressing the epithelial to mesenchymal transition induced by C3a.