Decoding anaphylatoxins: unveiling the molecular mechanisms of complement receptor activation and signaling.

Recent advances in cryo-electron microscopy (Cryo-EM) have revolutionized our understanding of the complement C5a/C3a receptors that are crucial in inflammation. A recent report by Yadav et al. has elucidated the activation, ligand binding, selectivity, and signaling bias of these receptors, thereby enhancing structure-guided drug discovery. This paves the way for more effective anti-inflammatory therapies that target these receptors with unprecedented precision.

Complement C3aR signaling: Immune and metabolic modulation and its impact on Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia among the elderly population. Despite its widespread prevalence, our comprehension of the intricate mechanisms governing the pathogenesis of the disease remains incomplete, posing a challenge for the development of efficient therapies. Pathologically characterized by the presence of amyloid ß plaques and neurofibrillary tau tangles, AD is also accompanied by the hyperactivation of glial cells and the immune system. The complement cascade, the evolutionarily conserved innate immune pathway, has emerged as a significant contributor to AD. This review focuses on one of the complement components, the C3a receptor (C3aR), covering its structure, ligand-receptor interaction, intracellular signaling and its functional consequences. Drawing insights from cellular and AD mouse model studies, we present the multifaceted role of complement C3aR signaling in AD and attempt to convey to the readers that C3aR acts as a crucial immune and metabolic modulator to influence AD pathogenesis. Building on this framework, the objective of this review is to inform future research endeavors and facilitate the development of therapeutic strategies for this challenging condition.

Follicular fluid C3a-peptide promotes oocyte maturation through F-actin aggregation.

BACKGROUND: Immature cumulus-oocyte complexes are retrieved to obtain mature oocytes by in vitro maturation (IVM), a laboratory tool in reproductive medicine to obtain mature oocytes. Unfortunately, the efficiency of IVM is not satisfactory. To circumvent this problem, we therefore intended to commence with the composition of ovarian follicular fluid (FF), an important microenvironment influencing oocyte growth. It is well known that FF has a critical role in oocyte development and maturation. However, the components in human FF remain largely unknown, particularly with regard to small molecular peptides. RESULTS: In current study, the follicular fluid derived from human mature and immature follicles were harvested. The peptide profiles of FF were further investigated by using combined ultrafiltration and LC-MS/MS. The differential peptides were preliminary determined by performing differentially expressed analysis. Human and mouse oocyte culture were used to verify the influence of differential peptides on oocyte development. Constructing plasmids, cell transfecting, Co-IP, PLA etc. were used to reveal the detail molecular mechanism. The results from differentially expressed peptide as well as cultured human and mouse oocytes analyses showed that highly conserved C3a-peptide, a cleavage product of complement C3a, definitely affected oocytes development. Intriguingly, C3a-peptide possessed a novel function that promoted F-actin aggregation and spindle migration, raised the percentage of oocytes at the MII stage, without increasing the chromosome aneuploidy ratio, especially in poor-quality oocytes. These effects of C3a-peptide were attenuated by C3aR morpholino inhibition, suggesting that C3a-peptide affected oocytes development by collaborating with its classical receptor, C3aR. Specially, we found that C3aR co-localized to the spindle with ß-tubulin to recruit F-actin toward the spindle and subcortical region of the oocytes through specific binding to MYO10, a key regulator for actin organization, spindle morphogenesis and positioning in oocytes. CONCLUSIONS: Our results provide a new perspective for improving IVM culture systems by applying FF components and also provide molecular insights into the physiological function of C3a-peptide, its interaction with C3aR, and their roles in enabling meiotic division of oocytes.

Protective role for C3aR in experimental chronic pyelonephritis.

Emerging evidence suggest that C3aR plays important roles in homeostasis, host defense and disease. Although it is known that C3aR is protective in several models of acute bacterial infections, the role for C3aR in chronic infection is largely unknown. Here we show that C3aR is protective in experimental chronic pyelonephritis. Global C3aR deficient (C3ar-/- ) mice had higher renal bacterial load, more pronounced renal histological lesions, increased renal apoptotic cell accumulation, tissue inflammation and extracellular matrix deposition following renal infection with uropathogenic E. coli (UPEC) strain IH11128, compared to WT control mice. Myeloid C3aR deficient (Lyz2-C3ar-/- ) mice exhibited a similar disease phenotype to global C3ar-/- mice. Pharmacological treatment with a C3aR agonist reduced disease severity in experimental chronic pyelonephritis. Furthermore, macrophages of C3ar-/- mice exhibited impaired ability to phagocytose UPEC. Our data clearly demonstrate a protective role for C3aR against experimental chronic pyelonephritis, macrophage C3aR plays a major role in the protection, and C3aR is necessary for phagocytosis of UPEC by macrophages. Our observation that C3aR agonist curtailed the pathology suggests a therapeutic potential for activation of C3aR in chronic infection.

C-reactive protein inhibits C3a/C3aR-dependent podocyte autophagy in favor of diabetic kidney disease.

Numerous studies have reported the pathogenic roles of C-reactive protein (CRP) and complement activation in diabetic kidney disease (DKD) individually. However, considering the potent regulatory effect of CRP on complement activation, it remains unclear whether CRP participates in DKD pathogenesis by regulating complement activation. Moreover, this work focuses on complement activation in rats, which aims at settling the dispute that whether rat CRP can activate the complement system. To address this question, the complement effectors C3a, C5a, and C5b-9 were examined in human patients with diabetic nephropathy (DN) and wt, Crp-/- , and huCRPtg rats with STZ-diabetic DKD. The Crp-/- rats showed more C3a accumulation in blood and glomeruli than wt and huCRPtg rats. The balance between autophagy and apoptosis was evaluated in DKD rats, and Crp-/- rats showed increased podocyte autophagy compared with wt and huCRPtg rats. Meanwhile, stable CRP-overexpression and CRP-knockout cell lines were established and used to demonstrate that CRP suppresses C3a-induced podocyte autophagy under high-glucose conditions. We further verified that the inhibition of C3a-induced podocyte autophagy by CRP was dependent on C3aR expression and that this effect could be reversed with a C3aR antagonist and agonist. Therefore, our findings provide evidence that CRP suppresses podocyte autophagy to accelerate the development of DKD by inhibiting C3a/C3aR axis signaling, which may help in the development of a new therapeutic strategy for the management of podocyte autophagy and DKD. In addition, rat CRP has been shown to be identical to human CRP in the activation of autologous complement and interspecific complement.

Astrocyte-microglia interaction through C3/C3aR pathway modulates neuropathic pain in rats model of chronic constriction injury.

Neuropathic pain (NP) is the cardinal symptom of neural injury, and its underlying molecular mechanism needs further investigation. Complements, especially complement 3 (C3), are involved in the pathophysiology of many neurological disorders, while the specific role of C3 in NP is still obscure. In this study, we found that both C3 and its receptor C3aR were upregulated in the spinal dorsal horn in a rat chronic constriction injury (CCI) model. In addition, C3 was mainly detected in astrocytes, while C3aR was expressed in microglia and neuron. Intrathecal injection of C3 antibody and C3aR antagonist alleviated NP in CCI model together with reduced M1 polarization of microglia. Our finding suggested that blockade of the C3/C3aR pathway might be a novel strategy for NP.

The molecular identity of the TLQP-21 peptide receptor.

The TLQP-21 neuropeptide has been implicated in functions as diverse as lipolysis, neurodegeneration and metabolism, thus suggesting an important role in several human diseases. Three binding targets have been proposed for TLQP-21: C3aR1, gC1qR and HSPA8. The aim of this review is to critically evaluate the molecular identity of the TLQP-21 receptor and the proposed multi-receptor mechanism of action. Several studies confirm a critical role for C3aR1 in TLQP-21 biological activity and a largely conserved mode of binding, receptor activation and signaling with C3a, its first-identified endogenous ligand. Conversely, data supporting a role of gC1qR and HSPA8 in TLQP-21 activity remain limited, with no signal transduction pathways being described. Overall, C3aR1 is the only receptor for which a necessary and sufficient role in TLQP-21 activity has been confirmed thus far. This conclusion calls into question the validity of a multi-receptor mechanism of action for TLQP-21 and should inform future studies.

The VGF-derived Peptide TLQP21 Impairs Purinergic Control of Chemotaxis and Phagocytosis in Mouse Microglia.

Microglial cells are considered as sensors of brain pathology by detecting any sign of brain lesions, infections, or dysfunction and can influence the onset and progression of neurological diseases. They are capable of sensing their neuronal environment via many different signaling molecules, such as neurotransmitters, neurohormones and neuropeptides. The neuropeptide VGF has been associated with many metabolic and neurological disorders. TLQP21 is a VGF-derived peptide and has been shown to signal via C3aR1 and C1qBP receptors. The effect of TLQP21 on microglial functions in health or disease is not known. Studying microglial cells in acute brain slices, we found that TLQP21 impaired metabotropic purinergic signaling. Specifically, it attenuated the ATP-induced activation of a K+ conductance, the UDP-stimulated phagocytic activity, and the ATP-dependent laser lesion-induced process outgrowth. These impairments were reversed by blocking C1qBP, but not C3aR1 receptors. While microglia in brain slices from male mice lack C3aR1 receptors, both receptors are expressed in primary cultured microglia. In addition to the negative impact on purinergic signaling, we found stimulating effects of TLQP21 in cultured microglia, which were mediated by C3aR1 receptors: it directly evoked membrane currents, stimulated basal phagocytic activity, evoked intracellular Ca2+ transient elevations, and served as a chemotactic signal. We conclude that TLQP21 has differential effects on microglia depending on C3aR1 activation or C1qBP-dependent attenuation of purinergic signaling. Thus, TLQP21 can modulate the functional phenotype of microglia, which may have an impact on their function in health and disease.SIGNIFICANCE STATEMENT The neuropeptide VGF and its peptides have been associated with many metabolic and neurological disorders. TLQP21 is a VGF-derived peptide that activates C1qBP receptors, which are expressed by microglia. We show here, for the first time, that TLQP21 impairs P2Y-mediated purinergic signaling and related functions. These include modulation of phagocytic activity and responses to injury. As purinergic signaling is central for microglial actions in the brain, this TLQP21-mediated mechanism might regulate microglial activity in health and disease. We furthermore show that, in addition to C1qBP, functional C3aR1 responses contribute to TLQP21 action on microglia. However, C3aR1 responses were only present in primary cultures but not in situ, suggesting that the expression of these receptors might vary between different microglial activation states.

In response to complement anaphylatoxin peptides C3a and C5a, human vascular endothelial cells migrate and mediate the activation of B-cells and polarization of T-cells.

The vascular endothelium has been discovered in the past several years to be important in shaping the cellular immune response. During the immune response the vascular endothelium is constantly perturbed by biologically potent molecules, including the complement activation peptides, C3a and C5a. Despite the importance of C3a and C5a in inflammation and immunity, their role in modulating lymphocyte function via activation of vascular endothelial cells is unknown. Accordingly, we investigated the regulated expression of the C3a and C5a receptors (complement anaphylatoxin C3a receptor [C3aR] and complement anaphylatoxin C5a receptor 1 [C5aR1]) on human umbilical vascular endothelial cells (HUVECs) and examined how C3a or C5a activation of HUVECs affects the activation and polarization of lymphatic cells. Our findings demonstrated that C3a and C5a increase C3aR and C5aR1 expression by HUVECs as well as directing their cellular transmigration and spreading through transwell filters. Moreover, C3a- or C5a-stimulated endothelial cells: (1) caused activation of B-lymphoblasts with significant increase in Fas Ligand (CD95L) (FasL), CD69, and IL-R1 expression, and (2) skewed T-lymphoblast cells toward a Th1 subtype, (CD4+ /CCR5+ ) that correlated with significant increase of IFN-γ. Collectively, these data indicate that C3a and C5a signaling is important in the activation and polarization of lymphocytes as they traffic through the vascular endothelium during the immune response.

Changes in VGF and C3aR1 gene expression in human adipose tissue in obesity.

The VGF gene, which has been shown to be metabolically associated with energy balance, glucose homeostasis, insulin secretion process, and biological processes related to overeating, is prominent in relation to obesity. TLQP-21 neuropeptide, derived from the VGF, is considered to promote lipolysis by the beta-adrenergic pathway through targeting the C3aR1 receptor located in the adipocyte membrane. In this study, we aimed to measure the expression levels of the VGF and C3aR1 genes in the adipose tissue of obese subjects and individuals with normal weight determined based on body mass index (BMI), and to reveal the correlation of these levels with obesity. VGF and C3aR1 gene expression levels were measured using Real Time Polymerase Chain Reaction (RT PCR) in the visceral adipose tissue (VAT) samples of 52 obese patients (BMI ≥ 35 kg/m2) and 21 non-obese controls (BMI = 18.5-24.9 kg/m2). The results were statistically analyzed. The VGF expression was lower and the C3aR1 gene expression was higher in obese patients compared to the non-obese control group (p < 0.05). In obese patients, there was a statistically significant positive correlation of 85.6% between VGF and C3aR1, in which when one level increased, the other also increased (p < 0.05, r = 0.856). The findings show that the VGF may be significantly associated with obesity and is very important since it is the first to measure the level of VGF gene expression in human adipose tissue. This research provides new evidence of a link between obesity and VGF/C3aR1 and in the future may help design strategies to combat obesity.

Mast cells and complement system: Ancient interactions between components of innate immunity.

The emergence and evolution of the complement system and mast cells (MCs) can be traced back to sea urchins and the ascidian Styela plicata, respectively. Acting as a cascade of enzymatic reactions, complement is activated through the classical (CP), the alternative (AP), and the lectin pathway (LP) based on the recognized molecules. The system's main biological functions include lysis, opsonization, and recruitment of phagocytes. MCs, beyond their classic role as master cells of allergic reactions, play a role in other settings, as well. Thus, MCs are considered as extrahepatic producers of complement proteins. They express various complement receptors, including those for C3a and C5a. C3a and C5a not only activate the C3aR and C5aR expressing MCs but also act as chemoattractants for MCs derived from different anatomic sites, such as from the bone marrow, human umbilical cord blood, or skin in vitro. Cross talk between MCs and complement is facilitated by the production of complement proteins by MCs and their activation by the MC tryptase. The coordinated activity between MCs and the complement system plays a key role, for example, in a number of allergic, cutaneous, and vascular diseases. At a molecular level, MCs and complement system interactions are based on the production of several complement zymogens by MCs and their activation by MC-released proteases. Additionally, at a cellular level, MCs act as potent effector cells of complement activation by expressing receptors for C3a and C5a through which their chemoattraction and activation are mediated by anaphylatoxins in a paracrine and autocrine fashion.

Bone marrow-derived macrophage contributes to fibrosing steatohepatitis through activating hepatic stellate cells.

The role of macrophages in fibrosing steatohepatitis is largely unclear. We characterized the origin and molecular mechanisms of macrophages and its targeted therapy of fibrosing steatohepatitis. Fibrosing steatohepatitis was established in Alms1 mutant (foz/foz) and C57BL/6J wildtype mice fed high-fat/high-cholesterol or methionine- and choline-deficient diet. Bone marrow transplantation was performed to track the macrophage origin in fibrosing steatohepatitis. Macrophages were depleted using liposomal clodronate. Primary macrophages were isolated from bone marrow for adoptive transfer into mice. We found that macrophage infiltration is induced in two mouse models of fibrosing steatohepatitis and human nonalcoholic steatohepatitis-fibrosis patients. Bone marrow-derived macrophages (BMMs) contribute to the hepatic macrophage accumulation in experimental fibrosing steatohepatitis. Depletion of hepatic BMMs by liposomal clodronate during liver injury attenuated fibrosing steatohepatitis, whilst BMMs depletion after liver injury delayed the regression of fibrosing steatohepatitis. The pro-fibrotic effect of macrophages was associated with reduced activation of hepatic stellate cells (HSCs), collagen deposition and hepatic expression of key pro-fibrotic factors (TIMP1, TIMP2, and TGFß1) and endoplasmic reticulum stress markers (GRP78, IRE1α, and PDI). Conversely, adoptive transfer of BMMs significantly aggravated fibrosing steatohepatitis. Moreover, macrophage-conditioned medium directly promoted the phenotypic transition of primary quiescent HSCs to activated HSCs; it enhanced activation and proliferation but decreased apoptosis of HSC cell lines (LX-2 and HSC-T6). The effect of BMMs in promoting fibrosing steatohepatitis was mediated by inducing key pro-fibrosis factors and signaling pathways including cytokine/chemokine, TGFß and complement cascade as assessed by cDNA expression array. Complement 3a receptor (C3ar1) was a predominant effector of macrophage mediated fibrosing steatohepatitis. Knockout of C3ar1 in mice blunted development of fibrosing steatohepatitis. In conclusion, BMMs promoted the progression of fibrosing steatohepatitis during injury, whereas macrophages reduced fibrosing steatohepatitis in the recovery phase of liver injury. Increasing anti-fibrotic macrophages and decreasing pro-fibrotic macrophages are promising approaches for fibrosing steatohepatitis. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Brain microvascular endothelial cells exhibit lower activation of the alternative complement pathway than glomerular microvascular endothelial cells.

Atypical hemolytic uremic syndrome (aHUS) and bone marrow transplantation-associated thrombotic microangiopathy (TA-TMA) are associated with excessive activation of the alternative complement pathway (AP) and with severe renal, but rarely cerebral, microvascular damage. Here, we compared AP activation and regulation in human glomerular and brain microvascular endothelial cells (GMVECs and BMVECs, respectively) unstimulated or stimulated by the proinflammatory cytokine, tumor necrosis factor (TNF). Compared with GMVECs and under both experimental conditions, BMVECs had increased gene expression of the AP-related genes C3, CFB, and C5 and decreased expression of CFD This was associated with increased expression in BMVECs (relative to GMVECs) of the genes for surface and soluble regulatory molecules (CD46, THBD, CD55, CFI, and CFH) suppressing formation of the AP C3 and C5 convertases. Of note, unlike GMVECs, BMVECs generated extremely low levels of C3a and C5a and displayed decreased activation of the AP (as measured by a lower percentage of Ba generation than GMVECs). Moreover, BMVECs exhibited increased function of CD141, mediating activation of the natural anticoagulant protein C, compared with GMVECs. We also found that the C3a receptor (C3aR) is present on both cell types and that TNF greatly increases C3AR1 expression in GMVECs, but only slightly in BMVECs. Higher AP activation and C3a generation in GMVECs than in BMVECs, coupled with an increase in C3aR production in TNF-stimulated GMVECs, provides a possible explanation for the predominance of renal damage, and the absence of cerebral injury, in individuals with episodes of aHUS and TA-TMA.

The C3a/C3aR axis mediates anti-inflammatory activity and protects against uropathogenic E coli-induced kidney injury in mice.

Both the C3a/C3aR and C5a/C5aR1 axes are regarded as important pathways for inducing and regulating inflammatory responses. It is well documented that the C5a/C5aR1 axis is a potent inflammatory mediator in the pathogenesis of many clinic disorders. However, our understanding of the role of the C3a/C3aR axis in renal disorders remains limited. Contrary to the C5a/C5aR axis, we now show that the C3a/C3aR axis has a protective role in uropathogenic Escherichia coli (UPEC)-induced renal injury. C3aR-/- mice were found to develop severe renal pathology compared to wild type mice, a pathology characterized by intense tissue damage and an increased bacterial load within the kidney. This was associated with an overwhelming production of pro-inflammatory mediators and increased neutrophil infiltration in the kidney. Bone marrow chimera experiments found that tissue damage and bacterial load were significantly reduced in C3aR-/- mice that received bone marrow from wild type mice, compared with that in mice re-populated with bone marrow from C3aR-/- mice. This supports a critical role for C3aR on myeloid cells in the pathological process. Pharmacological treatment of mice with a C3aR agonist reduced both the extent of tissue injury and bacterial load. Mechanistic analyses indicated that the C3a/C3aR axis downregulates the lipopolysaccharide-induced pro-inflammatory responses in macrophages and facilitates the phagocytosis of UPEC by phagocytes. Thus, our findings clearly demonstrate a protective role of the C3a/C3aR axis in UPEC-induced renal injury, conferred by the suppression of pro-inflammatory responses and enhanced phagocytosis by macrophages.

C3aR signaling and gliosis in response to neurodevelopmental damage in the cerebellum.

BACKGROUND: Conditional ablation of the Smarca5 gene in mice severely impairs the postnatal growth of the cerebellum and causes an ataxic phenotype. Comparative gene expression studies indicated that complement-related proteins were upregulated in the cerebellum of Smarca5 mutant mice. Complement proteins play critical roles within innate immune signaling pathways and, in the brain, are produced by glial cells under both normal and pathological conditions. The C3 complement protein-derived signaling peptide, C3a, has been implicated in contributing to both tissue damage and repair in conditions such as multiple sclerosis and stroke. Here, we investigated whether C3a receptor (C3aR) signaling promoted damage or repair in the developing cerebellum of Smarca5 mutant mice. METHODS: Brain and cerebellum lysates from single Smarca5 conditional knockout (Smarca5 cKO) mice, C3aR1 KO mice, or double mutant mice were used for qRT-PCR and immunoblotting to assess the contribution of C3aR to the Smarca5 cKO brain pathology. Immunohistochemistry was used to characterize alterations to astroglia and phagocyte cells in the developing cerebellum of each of the genotypes. RESULTS: C3aR signaling was observed to limit gliosis and promote granule neuron survival during postnatal cerebellar development. In Smarca5 cKO mice, disorganized astroglia with increased GFAP expression develops concurrently with cerebellar granule neuron loss and phagocyte invasion over the first 10 days following birth. Potential ligand precursors of C3aR-VGF and C3-were found to have upregulated expression and/or altered processing during this time. Phagocytes (microglia and macrophages) in both the control and Smarca5 mutant mice were the only cells observed to express C3aR. Loss of C3aR in the Smarca5 cKO cerebellum resulted in increased numbers of apoptotic cells and early phagocyte invasion into the external granule cell layer, as well as an exacerbated disorganization of the Bergmann glia. The loss of C3aR expression also attenuated an increase in the expression of the efferocytosis-related protein, MerTK, whose transcript was upregulated ~ 2.5-fold in the Smarca5 mutant cerebellum at P10. CONCLUSIONS: This data indicates that C3aR can play an important role in limiting astrogliosis and regulating phagocyte phenotypes following developmental cell loss in the brain.

C3aR and C5aR1 act as key regulators of human and mouse ß-cell function.

AIMS: Complement components 3 and 5 (C3 and C5) play essential roles in the complement system, generating C3a and C5a peptides that are best known as chemotactic and inflammatory factors. In this study we characterised islet expression of C3 and C5 complement components, and the impact of C3aR and C5aR1 activation on islet function and viability. MATERIALS AND METHODS: Human and mouse islet mRNAs encoding key elements of the complement system were quantified by qPCR and distribution of C3 and C5 proteins was determined by immunohistochemistry. Activation of C3aR and C5aR1 was determined using DiscoverX beta-arrestin assays. Insulin secretion from human and mouse islets was measured by radioimmunoassay, and intracellular calcium ([Ca2+]i), ATP generation and apoptosis were assessed by standard techniques. RESULTS: C3 and C5 proteins and C3aR and C5aR1 were expressed by human and mouse islets, and C3 and C5 were mainly localised to ß- and α-cells. Conditioned media from islets exposed for 1 h to 5.5 and 20 mM glucose stimulated C3aR and C5aR1-driven beta-arrestin recruitment. Activation of C3aR and C5aR1 potentiated glucose-induced insulin secretion from human and mouse islets, increased [Ca2+]i and ATP generation, and protected islets against apoptosis induced by a pro-apoptotic cytokine cocktail or palmitate. CONCLUSIONS: Our observations demonstrate a functional link between activation of components of the innate immune system and improved ß-cell function, suggesting that low-level chronic inflammation may improve glucose homeostasis through direct effects on ß-cells.

TLQP-21, A VGF-Derived Peptide Endowed of Endocrine and Extraendocrine Properties: Focus on In Vitro Calcium Signaling.

VGF gene encodes for a neuropeptide precursor of 68 kDa composed by 615 (human) and 617 (rat, mice) residues, expressed prevalently in the central nervous system (CNS), but also in the peripheral nervous system (PNS) and in various endocrine cells. This precursor undergoes proteolytic cleavage, generating a family of peptides different in length and biological activity. Among them, TLQP-21, a peptide of 21 amino acids, has been widely investigated for its relevant endocrine and extraendocrine activities. The complement complement C3a receptor-1 (C3aR1) has been suggested as the TLQP-21 receptor and, in different cell lines, its activation by TLQP-21 induces an increase of intracellular Ca2+. This effect relies both on Ca2+ release from the endoplasmic reticulum (ER) and extracellular Ca2+ entry. The latter depends on stromal interaction molecules (STIM)-Orai1 interaction or transient receptor potential channel (TRPC) involvement. After Ca2+ entry, the activation of outward K+-Ca2+-dependent currents, mainly the KCa3.1 currents, provides a membrane polarizing influence which offset the depolarizing action of Ca2+ elevation and indirectly maintains the driving force for optimal Ca2+ increase in the cytosol. In this review, we address the main endocrine and extraendocrine actions displayed by TLQP-21, highlighting recent findings on its mechanism of action and its potential in different pathological conditions.

Chemotaxis during neural crest migration.

Chemotaxis refers to the directional migration of cells towards external, soluble factors along their gradients. It is a process that is used by many different cell types during development for tissue organisation and the formation of embryonic structures, as well as disease like cancer metastasis. The neural crest (NC) is a multipotent, highly migratory cell population that contribute to a range of tissues. It has been hypothesised that NC migration, at least in part, is reliant on chemotactic signals. This review will explore the current evidence for proposed chemoattractants of NC cells, and outline mechanisms for the chemotactic response of the NC to them.

Complement component C3aR constitutes a novel regulator for chick eye morphogenesis.

Complement components have been implicated in a wide variety of functions including neurogenesis, proliferation, cell migration, differentiation, cancer, and more recently early development and regeneration. Following our initial observations indicating that C3a/C3aR signaling induces chick retina regeneration, we analyzed its role in chick eye morphogenesis. During eye development, the optic vesicle (OV) invaginates to generate a bilayer optic cup (OC) that gives rise to the retinal pigmented epithelium (RPE) and neural retina. We show by immunofluorescence staining that C3 and the receptor for C3a (the cleaved and active form of C3), C3aR, are present in chick embryos during eye morphogenesis in the OV and OC. Interestingly, C3aR is mainly localized in the nuclear compartment at the OC stage. Loss of function studies at the OV stage using morpholinos or a blocking antibody targeting the C3aR (anti-C3aR Ab), causes eye defects such as microphthalmia and defects in the ventral portion of the eye that result in coloboma. Such defects were not observed when C3aR was disrupted at the OC stage. Histological analysis demonstrated that microphthalmic eyes were unable to generate a normal optic stalk or a closed OC. The dorsal/ventral patterning defects were accompanied by an expansion of the ventral markers Pax2, cVax and retinoic acid synthesizing enzyme raldh-3 (aldh1a3) domains, an absence of the dorsal expression of Tbx5 and raldh-1 (aldh1a1) and a re-specification of the ventral RPE to neuroepithelium. In addition, the eyes showed overall decreased expression of Gli1 and a change in distribution of nuclear ß-catenin, suggesting that Shh and Wnt pathways have been affected. Finally, we observed prominent cell death along with a decrease in proliferating cells, indicating that both processes contribute to the microphthalmic phenotype. Together our results show that C3aR is necessary for the proper morphogenesis of the OC. This is the first report implicating C3aR in eye development, revealing an unsuspected hitherto regulator for proper chick eye morphogenesis.

A pathogenic role of complement in arterial hypertension and hypertensive end organ damage.

The self-amplifying cascade of messenger and effector molecules of the complement system serves as a powerful danger-sensing system that protects the host from a hostile microbial environment, while maintaining proper tissue and organ function through effective clearance of altered or dying cells. As an important effector arm of innate immunity, it also plays important roles in the regulation of adaptive immunity. Innate and adaptive immune responses have been identified as crucial players in the pathogenesis of arterial hypertension and hypertensive end organ damage. In line with this view, complement activation may drive the pathology of hypertension and hypertensive injury through its impact on innate and adaptive immune responses. It is well known that complement activation can cause tissue inflammation and injury and complement-inhibitory drugs are effective treatments for several inflammatory diseases. In addition to these proinflammatory properties, complement cleavage fragments of C3 and C5 can exert anti-inflammatory effects that dampen the inflammatory response to injury. Recent experimental data strongly support a role for complement in arterial hypertension. The remarkably similar clinical and histopathological features of malignant nephrosclerosis and atypical hemolytic uremic syndrome, which is driven by complement activation, suggest a role for complement also in the development of malignant nephrosclerosis. Herein, we will review canonical and noncanonical pathways of complement activation as the framework to understand the multiple roles of complement in arterial hypertension and hypertensive end organ damage.