Identification of the C3a receptor (C3AR1) as the target of the VGF-derived peptide TLQP-21 in rodent cells

Systematic identification of genomic hotspots for high-yield protein production in CHO cells

The efficient and stable production of therapeutic proteins in Chinese hamster ovary (CHO) cells hinges on robust cell line development (CLD). Traditional methods relying on random transgene integration often result in clonal variability, requiring extensive and resource-intensive screening. To address this limitation, we established a systematic, multiomics-driven framework that integrates 202 RNA-sequencing datasets and whole-genome sequencing data to identify genomic "hotspot" loci for precise and high-yield transgene integration. From an initial pool of 20 candidate loci, 5 top-performing hotspots were validated using site-specific integration in CHO-DG44 cells via the CRISPR/Cas9 system with Recombinase-mediated cassette exchange (RMCE). These genomic hotspots achieved 2.2- to 15.0-fold higher relative specific productivity compared to previously known controls (Fer1L4 and Locus1 sites), across multiple therapeutic proteins, including a lysosomal storage disorder-related enzyme and an Immunoglobulin G (IgG)-related monoclonal antibody (mAb) expression. This study offers a transformative approach to CLD, achieving significant improvements in productivity, genomic stability, and efficiency, as well as paving the way for enhanced biopharmaceutical manufacturing.

VGF and the VGF-derived peptide AQEE30 stimulate osteoblastic bone formation through the C3a receptor

New therapeutic targets, especially those that stimulate bone formation in cortical bone, are needed to overcome the limitations of current antiosteoporotic drugs. We previously demonstrated that factors secreted from megakaryocytes (MKs) promote bone formation. Here we conducted a proteomic analysis to identify a novel bone-forming factor from MK secretions. We revealed that Vgf, a nerve growth factor-responsive gene, and its derived active peptide AQEE30 in MK-conditioned medium play important roles in osteoblast proliferation and in vitro bone formation. In both Vgf-deficient male and female mice, the cortical bone mass was significantly decreased due to reductions in osteoblast number and bone formation activity. AQEE30 stimulated intracellular cyclic adenosine monophosphate (cAMP) levels and protein kinase A (PKA) activity in osteoblasts, whereas an adenylyl cyclase inhibitor blocked AQEE30-stimulated osteoblast proliferation and in vitro bone formation. Complement C3a receptor-1 (C3AR1) was expressed and interacted with AQEE30 in osteoblasts, and C3AR1 inhibition blocked all AQEE30-induced changes, including stimulated proliferation, bone formation and cAMP production, in osteoblasts. Injecting mini-PEGylated AQEE30 into calvaria increased the number of osteocalcin-positive cells and new bone formation. In conclusion, this study reveals a novel role of VGF in bone formation, particularly in cortical bone, and shows that AQEE30, a VGF-derived peptide, mediates this role by activating cAMP-PKA signaling via the C3AR1 receptor in osteoblasts.

Neuropeptide Precursor VGF Promotes Liver Metastatic Colonization of Gαq Mutant Uveal Melanoma by Facilitating Tumor Microenvironment via Paracrine Loops

Uveal melanoma (UM), the predominant primary ocular malignancy, often progresses to liver metastasis with limited therapeutic options. The interplay of the tumor microenvironment, encompassing secreted soluble factors, plays a crucial role in facilitating liver metastasis. In this study, the role is elucidated of the neural growth factor-inducible gene (VGF), a secreted neuropeptide precursor, in Gαq mutant UM. Employing a multiomics approach, encompassing transcriptomic and secretomic analyses, the intricate involvement of VGF in UM progression is unveiled. VGF is upregulated in Gαq mutant UM cells and associated with poor prognosis of UM patients. Targeting VGF significantly suppressed the growth of UM in vitro and in vivo. Further evidence shows that VGF is regulated by Gαq through MAPK/CREB pathway. Mechanistically, CREB modulates VGF expression by directly binding to consensus DNA response elements in the promoters of the VGF gene. Combined inhibition of Gαq and MEK remarkably reduces tumor burden in the UM xenograft model. Notably, VGF triggers liver metastatic colonization of UM and activates the fibrosis of hepatic stellate cells (HSCs), creating a favorable microenvironment, through an autocrine and paracrine loop. Furthermore, VGF directly binds to TGFBR2 and regulates TGF-β-SMAD signaling pathway, thereby regulating genes associated with endothelial-mesenchymal transition (EMT) to promote metastasis. Taken together, these findings identify VGF as a pivotal driver in the progression and metastasis of Gαq mutant UM and confers a promising therapeutic target and strategy for UM patients.

2'3'-cGAMP interactome identifies 2'3'-cGAMP/Rab18/FosB signaling in cell migration control independent of innate immunity

c-di-GAMP was first identified in bacteria to promote colonization, while mammalian 2'3'-cGAMP is synthesized by cGAS to activate STING for innate immune stimulation. However, 2'3'-cGAMP function beyond innate immunity remains elusive. Here, we report that 2'3'-cGAMP promotes cell migration independent of innate immunity. 2'3'-cGAMP interactome analysis identifies the small GTPase Rab18 as a 2'3'-cGAMP binding partner and effector in cell migration control. Mechanistically, 2'3'-cGAMP binds Rab18 to facilitate GTP loading and subsequent Rab18 activation, which further promotes FosB transcription in facilitating cell migration. Induced synthesis of endogenous 2'3'-cGAMP by intrabreast tumor bacterium S. aureus infection or low-dose doxorubicin treatment facilitates cell migration depending on the cGAS/cGAMP/Rab18/FosB signaling. We find that lovastatin induces Rab18 deprenylation that abolishes 2'3'-cGAMP recognition therefore suppressing cell migration. Together, our study reveals a previously unidentified 2'3'-cGAMP function in cell migration control via the 2'3'-cGAMP/Rab18/FosB signaling that provides additional insights into clinical applications of 2'3'-cGAMP.

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 β 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.

Harmine and exendin-4 combination therapy safely expands human β cell mass in vivo in a mouse xenograft system

Five hundred thirty-seven million people globally suffer from diabetes. Insulin-producing β cells are reduced in number in most people with diabetes, but most individuals still have some residual β cells. However, none of the many diabetes drugs in common use increases human β cell numbers. Recently, small molecules that inhibit dual tyrosine-regulated kinase 1A (DYRK1A) have been shown to induce immunohistochemical markers of human β cell replication, and this is enhanced by drugs that stimulate the glucagon-like peptide 1 (GLP1) receptor (GLP1R) on β cells. However, it remains to be demonstrated whether these immunohistochemical findings translate into an actual increase in human β cell numbers in vivo. It is also unknown whether DYRK1A inhibitors together with GLP1R agonists (GLP1RAs) affect human β cell survival. Here, using an optimized immunolabeling-enabled three-dimensional imaging of solvent-cleared organs (iDISCO+) protocol in mouse kidneys bearing human islet grafts, we demonstrate that combination of a DYRK1A inhibitor with exendin-4 increases actual human β cell mass in vivo by a mean of four- to sevenfold in diabetic and nondiabetic mice over 3 months and reverses diabetes, without alteration in human α cell mass. The augmentation in human β cell mass occurred through mechanisms that included enhanced human β cell proliferation, function, and survival. The increase in human β cell survival was mediated, in part, by the islet prohormone VGF. Together, these findings demonstrate the therapeutic potential and favorable preclinical safety profile of the DYRK1A inhibitor-GLP1RA combination for diabetes treatment.

The NERP-4-SNAT2 axis regulates pancreatic β-cell maintenance and function

Insulin secretion from pancreatic β cells is regulated by multiple stimuli, including nutrients, hormones, neuronal inputs, and local signalling. Amino acids modulate insulin secretion via amino acid transporters expressed on β cells. The granin protein VGF has dual roles in β cells: regulating secretory granule formation and functioning as a multiple peptide precursor. A VGF-derived peptide, neuroendocrine regulatory peptide-4 (NERP-4), increases Ca2+ influx in the pancreata of transgenic mice expressing apoaequorin, a Ca2+-induced bioluminescent protein complex. NERP-4 enhances glucose-stimulated insulin secretion from isolated human and mouse islets and β-cell-derived MIN6-K8 cells. NERP-4 administration reverses the impairment of β-cell maintenance and function in db/db mice by enhancing mitochondrial function and reducing metabolic stress. NERP-4 acts on sodium-coupled neutral amino acid transporter 2 (SNAT2), thereby increasing glutamine, alanine, and proline uptake into β cells and stimulating insulin secretion. SNAT2 deletion and inhibition abolish the protective effects of NERP-4 on β-cell maintenance. These findings demonstrate a novel autocrine mechanism of β-cell maintenance and function that is mediated by the peptide-amino acid transporter axis.

Targeted and selective knockout of the TLQP-21 neuropeptide unmasks its unique role in energy homeostasis

OBJECTIVE

Pro-peptide precursors are processed into biologically active peptide hormones or neurotransmitters, each playing an essential role in physiology and disease. Genetic loss of function of a pro-peptide precursor results in the simultaneous ablation of all biologically-active peptides within that precursor, often leading to a composite phenotype that can be difficult to align with the loss of specific peptide components. Due to this biological constraint and technical limitations, mice carrying the selective ablation of individual peptides encoded by pro-peptide precursor genes, while leaving the other peptides unaffected, have remained largely unaddressed.

METHODS

We developed and characterized a mouse model carrying the selective knockout of the TLQP-21 neuropeptide (ΔTLQP-21) encoded by the Vgf gene. To achieve this goal, we used a knowledge-based approach by mutating a codon in the Vgf sequence leading to the substitution of the C-terminal Arginine of TLQP-21, which is the pharmacophore as well as an essential cleavage site from its precursor, into Alanine (R21→A).

RESULTS

We provide several independent validations of this mouse, including a novel in-gel digestion targeted mass spectrometry identification of the unnatural mutant sequence, exclusive to the mutant mouse. ΔTLQP-21 mice do not manifest gross behavioral and metabolic abnormalities and reproduce well, yet they have a unique metabolic phenotype characterized by an environmental temperature-dependent resistance to diet-induced obesity and activation of the brown adipose tissue.

CONCLUSIONS

The ΔTLQP-21 mouse line can be a valuable resource to conduct mechanistic studies on the necessary role of TLQP-21 in physiology and disease, while also serving as a platform to test the specificity of novel antibodies or immunoassays directed at TLQP-21. Our approach also has far-reaching implications by informing the development of knowledge-based genetic engineering approaches to generate selective loss of function of other peptides encoded by pro-hormones genes, leaving all other peptides within the pro-protein precursor intact and unmodified.

Targeted and selective knockout of the TLQP-21 neuropeptide unmasks its unique role in energy homeostasis

Pro-peptide precursors are processed into biologically active peptide hormones or neurotransmitters, each playing an essential role in physiology and disease. Genetic loss of function of a pro-peptide precursor results in the simultaneous ablation of all biologically-active peptides within that precursor, often leading to a composite phenotype that can be difficult to align with the loss of specific peptide components. Due to this biological constraint and technical limitations, mice carrying the selective ablation of individual peptides encoded by pro-peptide precursor genes, while leaving the other peptides unaffected, have remained largely unaddressed. Here, we developed and characterized a mouse model carrying the selective knockout of the TLQP-21 neuropeptide (ΔTLQP-21) encoded by the Vgf gene. To achieve this goal, we used a knowledge-based approach by mutating a codon in the Vgf sequence leading to the substitution of the C-terminal Arginine of TLQP-21, which is the pharmacophore as well as an essential cleavage site from its precursor, into Alanine (R ₂₁ →A). We provide several independent validations of this mouse, including a novel in-gel digestion targeted mass spectrometry identification of the unnatural mutant sequence, exclusive to the mutant mouse. ΔTLQP-21 mice do not manifest gross behavioral and metabolic abnormalities and reproduce well, yet they have a unique metabolic phenotype characterized by a temperature-dependent resistance to diet-induced obesity and activation of the brown adipose tissue.

TLQP-21 is a low potency partial C3aR activator on human primary macrophages

TLQP-21 is a 21-amino acid neuropeptide derived from the VGF precursor protein. TLQP-21 is expressed in the nervous system and neuroendocrine glands, and demonstrates pleiotropic roles including regulating metabolism, nociception and microglial functions. Several possible receptors for TLQP-21 have been identified, with complement C3a receptor (C3aR) being the most commonly reported. However, few studies have characterised the activity of TLQP-21 in immune cells, which represent the major cell type expressing C3aR. In this study, we therefore aimed to define the activity of both human and mouse TLQP-21 on cell signalling in primary human and mouse macrophages. We first confirmed that TLQP-21 induced ERK signalling in CHO cells overexpressing human C3aR, and did not activate human C5aR1 or C5aR2. TLQP-21 mediated ERK signalling was also observed in primary human macrophages. However, the potency for human TLQP-21 was 135,000-fold lower relative to C3a, and only reached 45% at the highest dose tested (10 μM). Unlike in humans, mouse TLQP-21 potently triggered ERK signalling in murine macrophages, reaching near full activation, but at ~10-fold reduced potency compared to C3a. We further confirmed the C3aR dependency of the TLQP-21 activities. Our results reveal significant discrepancy in TLQP-21 C3aR activity between human and murine receptors, with mouse TLQP-21 being consistently more potent than the human counterpart in both systems. Considering the supraphysiological concentrations of hTLQP-21 needed to only partially activate macrophages, it is likely that the actions of TLQP-21, at least in these immune cells, may not be mediated by C3aR in humans.

Structure of AQEE-30 of VGF Neuropeptide in Membrane-Mimicking Environments

AQEE-30 is one of the VGF peptides, which are derived from the VGF polypeptide precursor, and related to various physiological phenomena including neuroprotective effects in Huntington's disease and amyotrophic lateral sclerosis (ALS). Although various functions of AQEE-30 have been reported so far, the structure of this peptide has not been reported yet. In this study, the structure of human AQEE-30 was investigated in hexafluoroisopropanol (HFIP) and dodecyl phosphocholine (DPC) micelle solutions, using circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. CD results showed that AQEE-30 had a partial helical structure in aqueous buffer, and the helical structure was stabilized in the HFIP and DPC micelle solutions. The 3D structures determined by NMR spectroscopy showed that AQEE-30 adopted mainly α-helical structure in both the HFIP and DPC micelle solutions. The surface of AQEE-30 showed that it was predominantly negatively charged. The residues from 601 to 611 in both the HFIP and DPC micelle solutions showed amphiphilicity with four negatively charged residues, glutamate. The C-terminal consecutive arginine residues formed a partial positively charged surface. These results suggest an α-helical active structure of AQEE-30 in the cell-membrane environment.

VGF: A prospective biomarker and therapeutic target for neuroendocrine and nervous system disorders

Neuroendocrine regulatory polypeptide VGF (nerve growth factor inducible) was firstly found in the rapid induction of nerve growth factor on PC12 cells. It was selectively distributed in neurons and many neuroendocrine tissues. This paper reviewed the latest literatures on the gene structure, transcriptional regulation, protein processing, distribution and potential receptors of VGF. The neuroendocrine roles of VGF and its derived polypeptides in regulating energy, water electrolyte balance, circadian rhythm and reproductive activities were also summarized. Furthermore, based on the experimental evidence in vivo and in vitro, dysregulation of VGF in different neuroendocrine diseases and the possible mechanism mediated by VGF polypeptides were discussed. We next discussed the potential as the clinical diagnosis and therapy for VGF related diseases in the future.

Thalamocortical axons regulate neurogenesis and laminar fates in the early sensory cortex

This study addresses how the cerebral cortex is partitioned into specialized areas during development. Although both early embryonic patterning and postnatal synaptic input from sensory thalamic nuclei are known to be critical, early roles of thalamic axons in area-specific regulation of cortical neurogenesis are poorly understood. We examined this by developing a genetic mouse model in which thalamocortical projections fail to properly form during embryogenesis, and found these axons are required not only for an enhanced production of superficial layer neurons but also for promoting the layer 4 cell fate, a hallmark of the primary sensory cortex. These findings provide a mechanism by which thalamocortical axons complement the intrinsic programs of neurogenesis and early fate specification.

Area-specific axonal projections from the mammalian thalamus shape unique cellular organization in target areas in the adult neocortex. How these axons control neurogenesis and early neuronal fate specification is poorly understood. By using mutant mice lacking the majority of thalamocortical axons, we show that these axons are required for the production and specification of the proper number of layer 4 neurons in primary sensory areas by the neonatal stage. Part of these area-specific roles is played by the thalamus-derived molecule, VGF. Our work reveals that extrinsic cues from sensory thalamic projections have an early role in the formation of cortical cytoarchitecture by enhancing the production and specification of layer 4 neurons.

Complement C3 and C3aR mediate different aspects of emotional behaviours; relevance to risk for psychiatric disorder

Complement is a key component of the immune system with roles in inflammation and host-defence. Here we reveal novel functions of complement pathways impacting on emotional reactivity of potential relevance to the emerging links between complement and risk for psychiatric disorder. We used mouse models to assess the effects of manipulating components of the complement system on emotionality. Mice lacking the complement C3a Receptor (C3aR^-/-) demonstrated a selective increase in unconditioned (innate) anxiety whilst mice deficient in the central complement component C3 (C3^-/-) showed a selective increase in conditioned (learned) fear. The dissociable behavioural phenotypes were linked to different signalling mechanisms. Effects on innate anxiety were independent of C3a, the canonical ligand for C3aR, consistent with the existence of an alternative ligand mediating innate anxiety, whereas effects on learned fear were due to loss of iC3b/CR3 signalling. Our findings show that specific elements of the complement system and associated signalling pathways contribute differentially to heightened states of anxiety and fear commonly seen in psychopathology.

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.

Dissociable effects of complement C3 and C3aR on survival and morphology of adult born hippocampal neurons, pattern separation, and cognitive flexibility in male mice

Adult hippocampal neurogenesis (AHN) is a form of ongoing plasticity in the brain that supports specific aspects of cognition. Disruptions in AHN have been observed in neuropsychiatric conditions presenting with inflammatory components and are associated with impairments in cognition and mood. Recent evidence highlights important roles of the complement system in synaptic plasticity and neurogenesis during neurodevelopment and in acute learning and memory processes. In this work we investigated the impact of the complement C3/C3aR pathway on AHN and its functional implications for AHN-related behaviours. In C3-/- mice, we found increased numbers and accelerated migration of adult born granule cells, indicating that absence of C3 leads to abnormal survival and distribution of adult born neurons. Loss of either C3 or C3aR affected the morphology of immature neurons, reducing morphological complexity, though these effects were more pronounced in the absence of C3aR. We assessed functional impacts of the cellular phenotypes in an operant spatial discrimination task that assayed AHN sensitive behaviours. Again, we observed differences in the effects of manipulating C3 or C3aR, in that whilst C3aR-/- mice showed evidence of enhanced pattern separation abilities, C3-/- mice instead demonstrated impaired behavioural flexibility. Our findings show that C3 and C3aR manipulation have distinct effects on AHN that impact at different stages in the development and maturation of newly born neurons, and that the dissociable cellular phenotypes are associated with specific alterations in AHN-related behaviours.

VGF as a biomarker and therapeutic target in neurodegenerative and psychiatric diseases

Neurosecretory protein VGF (non-acronymic) belongs to the granin family of neuropeptides. VGF and VGF-derived peptides have been repeatedly identified in well-powered and well-designed multi-omic studies as dysregulated in neurodegenerative and psychiatric diseases. New therapeutics is urgently needed for these devastating and costly diseases, as are new biomarkers to improve disease diagnosis and mechanistic understanding. From a list of 537 genes involved in Alzheimer's disease pathogenesis, VGF was highlighted by the Accelerating Medicines Partnership in Alzheimer's disease as the potential therapeutic target of greatest interest. VGF levels are consistently decreased in brain tissue and CSF samples from patients with Alzheimer's disease compared to controls, and its levels correlate with disease severity and Alzheimer's disease pathology. In the brain, VGF exists as multiple functional VGF-derived peptides. Full-length human VGF1-615 undergoes proteolytic processing by prohormone convertases and other proteases in the regulated secretory pathway to produce at least 12 active VGF-derived peptides. In cell and animal models, these VGF-derived peptides have been linked to energy balance regulation, neurogenesis, synaptogenesis, learning and memory, and depression-related behaviours throughout development and adulthood. The C-terminal VGF-derived peptides, TLQP-62 (VGF554-615) and TLQP-21 (VGF554-574) have differential effects on Alzheimer's disease pathogenesis, neuronal and microglial activity, and learning and memory. TLQP-62 activates neuronal cell-surface receptors and regulates long-term hippocampal memory formation. TLQP-62 also prevents immune-mediated memory impairment, depression-like and anxiety-like behaviours in mice. TLQP-21 binds to microglial cell-surface receptors, triggering microglial chemotaxis and phagocytosis. These actions were reported to reduce amyloid-β plaques and decrease neuritic dystrophy in a transgenic mouse model of familial Alzheimer's disease. Expression differences of VGF-derived peptides have also been associated with frontotemporal lobar dementias, amyotrophic lateral sclerosis, Lewy body diseases, Huntington's disease, pain, schizophrenia, bipolar disorder, depression and antidepressant response. This review summarizes current knowledge and highlights questions for future investigation regarding the roles of VGF and its dysregulation in neurodegenerative and psychiatric disease. Finally, the potential of VGF and VGF-derived peptides as biomarkers and novel therapeutic targets for neurodegenerative and psychiatric diseases is highlighted.

Targeting Complement C3a Receptor to Improve Outcome After Ischemic Brain Injury

Ischemic stroke is a major cause of disability. No efficient therapy is currently available, except for the removal of the occluding blood clot during the first hours after symptom onset. Loss of function after stroke is due to cell death in the infarcted tissue, cell dysfunction in the peri-infarct region, as well as dysfunction and neurodegeneration in remote brain areas. Plasticity responses in spared brain regions are a major contributor to functional recovery, while secondary neurodegeneration in remote regions is associated with depression and impedes the long-term outcome after stroke. Hypoxic-ischemic encephalopathy due to birth asphyxia is the leading cause of neurological disability resulting from birth complications. Despite major progress in neonatal care, approximately 50% of survivors develop complications such as mental retardation, cerebral palsy or epilepsy. The C3a receptor (C3aR) is expressed by many cell types including neurons and glia. While there is a body of evidence for its deleterious effects in the acute phase after ischemic injury to the adult brain, C3aR signaling contributes to better outcome in the post-acute and chronic phase after ischemic stroke in adults and in the ischemic immature brain. Here we discuss recent insights into the novel roles of C3aR signaling in the ischemic brain with focus on the therapeutic opportunities of modulating C3aR activity to improve the outcome after ischemic stroke and birth asphyxia.

The molecular mechanism of vgf in appetite, lipids, and insulin regulation

Obesity is an indication of an imbalance between energy expenditure and food intake. It is a complicated disease of epidemic proportions as it involves many factors and organs. Sedentary lifestyles and overeating have caused a substantial rise in people with obesity and type 2 diabetes. Thus, the discovery of successful and sustainable therapies for these chronic illnesses is critical. However, the mechanisms of obesity and diabetes and the crosstalk between these diseases are still ambiguous. Numerous studies are being done to study these mechanisms, with updates made frequently. VGF peptide and its derivatives are anticipated to have a role in the development of obesity and diabetes. However, contradictory studies have produced conflicting findings on the function of VGF. Therefore, in this review, we attempt to clarify and explain the role of VGF peptides in the brain, pancreas, and adipose tissue in the development of obesity.

Complement Component C3: A Novel Biomarker Participating in the Pathogenesis of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is currently the most common cause of chronic liver disorder worldwide. The pathological spectrum of NAFLD ranges from simple steatosis to non-alcoholic steatohepatitis (NASH) that induces progressive liver cirrhosis and eventually hepatocellular carcinoma (HCC). However, the molecular mechanisms driving the transformation of NASH are obscure. There is a compelling need for understanding the pathogenic mechanisms of NASH, and thereby providing new insight into mechanism-based therapy. Currently, several studies reported that complement system, an innate immune system, played an important role in the pathogenesis of NAFLD, which was also proved by our recent study. Complement component 3 (C3), a protein of the innate immune system, plays a hub role in the complement system. Herein, we present a review on the role and molecular mechanism of C3 in NASH as well as its implication in NASH diagnosis and treatment.

(-)-Oleocanthal Nutraceuticals for Alzheimer's Disease Amyloid Pathology: Novel Oral Formulations, Therapeutic, and Molecular Insights in 5xFAD Transgenic Mice Model

Alzheimer’s disease (AD) is a complex progressive neurodegenerative disorder affecting humans mainly through the deposition of Aβ-amyloid (Aβ) fibrils and accumulation of neurofibrillary tangles in the brain. Currently available AD treatments only exhibit symptomatic relief but do not generally intervene with the amyloid and tau pathologies. The extra-virgin olive oil (EVOO) monophenolic secoiridoid S-(–)-oleocanthal (OC) showed anti-inflammatory activity through COX system inhibition with potency comparable to the standard non-steroidal anti-inflammatory drug (NSAID) like ibuprofen. OC also showed positive in vitro, in vivo, and clinical therapeutic effects against cardiovascular diseases, many malignancies, and AD. Due to its pungent, astringent, and irritant taste, OC should be formulated in acceptable dosage form before its oral use as a potential nutraceutical. The objective of this study is to develop new OC oral formulations, assess whether they maintained OC activity on the attenuation of β-amyloid pathology in a 5xFAD mouse model upon 4-month oral dosing use. Exploration of potential OC formulations underlying molecular mechanism is also within this study scope. OC powder formulation (OC-PF) and OC-solid dispersion formulation with erythritol (OC-SD) were prepared and characterized using FT-IR spectroscopy, powder X-ray diffraction, and scanning electron microscopy (ScEM) analyses. Both formulations showed an improved OC dissolution profile. OC-PF and OC-SD improved memory deficits of 5xFAD mice in behavioral studies. OC-PF and OC-SD exhibited significant attenuation of the accumulation of Aβ plaques and tau phosphorylation in the brain of 5xFAD female mice. Both formulations markedly suppressed C3AR1 (complement component 3a receptor 1) activity by targeting the downstream marker STAT3. Collectively, these results demonstrate the potential for the application of OC-PF as a prospective nutraceutical or dietary supplement to control the progression of amyloid pathogenesis associated with AD.

Hyperactive Behavior and Altered Brain Morphology in Adult Complement C3a Receptor Deficient Mice

The C3a receptor (C3aR) is a seven trans-membrane domain G-protein coupled receptor with a range of immune modulatory functions. C3aR is activated by the third complement component (C3) activation derived peptide C3a and a neuropeptide TLQP-21. In the central nervous system (CNS), C3aR is expressed by neural progenitors, neurons as well as glial cells. The non-immune functions of C3aR in the adult CNS include regulation of basal neurogenesis, injury-induced neural plasticity, and modulation of glial cell activation. In the developing brain, C3aR and C3 have been shown to play a role in neural progenitor cell proliferation and neuronal migration with potential implications for autism spectrum disorder, and adult C3aR deficient (C3aR^−/−) mice were reported to exhibit subtle deficit in recall memory. Here, we subjected 3 months old male C3aR^−/− mice to a battery of behavioral tests and examined their brain morphology. We found that the C3aR^−/− mice exhibit a short-term memory deficit and increased locomotor activity, but do not show any signs of autistic behavior as assessed by self-grooming behavior. We also found regional differences between the C3aR^−/− and wild-type (WT) mice in the morphology of motor and somatosensory cortex, as well as amygdala and hippocampus. In summary, constitutive absence of C3aR signaling in mice leads to neurodevelopmental abnormalities that persist into adulthood and are associated with locomotive hyperactivity and altered cognitive functions.

Evaluation of VGF peptides as potential anti-obesity candidates in pre-clinical animal models

VGF is a peptide precursor expressed in neuroendocrine cells that is suggested to play a role in the regulation of energy homeostasis. VGF is proteolytically cleaved to yield multiple bioactive peptides. However, the specific actions of VGF-derived peptides on energy homeostasis remain unclear. The aim of the present work was to investigate the role of VGF-derived peptides in energy homeostasis and explore the pharmacological actions of VGF-derived peptides on body weight in preclinical animal models. VGF-derived peptides (NERP-1, NERP-2, PGH-NH₂, PGH-OH, NERP-4, TLQP-21, TLQP-30, TLQP-62, HHPD-41, AQEE-30, and LQEQ-19) were synthesized and screened for their ability to affect neuronal activity in vitro on hypothalamic brain slices and modulate food intake and energy expenditure after acute central administration in vivo. In addition, the effects of NERP-1, NERP-2, PGH-NH₂, TLQP-21, TLQP-62, and HHPD-41 on energy homeostasis were studied after chronic central infusion. NERP-1, PGH-NH₂, HHPD-41, and TLQP-62 increased the functional activity of hypothalamic neuronal networks. However, none of the peptides altered energy homeostasis after either acute or chronic ICV administration. The present data do not support the potential use of the tested VGF-derived peptides as novel anti-obesity drug candidates.

TLQP-21 changes in response to a glucose load

BACKGROUND

The TLQP-21 peptide potentiates glucose-stimulated insulin secretion, hence we investigated its endogenous response to glucose.

METHODS

Fasted mice received intraperitoneal glucose (3 g/kg), or saline (controls), and were sacrificed 30 and 120 min later (4 groups, n = 6/group). We investigated TLQP-21 in pancreas and plasma using immunohistochemistry, enzyme-linked immunosorbent assay (ELISA) and high performance liquid chromatography (HPLC), as well as TLQP-21 receptors (gC1q-R and C3a-R1) expression in pancreas by immunohistochemistry.

RESULTS

In pancreas, TLQP-immunoreactivity (TLQP-ir.) was shown in insulin-, glucagon- and somatostatin-containing cells. Upon glucose, TLQP-ir. decreased at 30 min (∼40 % vs. controls), while returning to basal values at 120 min. In all groups, C3a-R1 was localized in ∼50 % of TLQP labelled islet cells (mostly central), while gC1q-R was detected in ∼25 % of TLQP cells (mainly peripheral). HPLC fractions of control pancreas extracts, assessed by ELISA, confirmed the presence of a TLQP-21 compatible-form (∼2.5 kDa MW). In plasma, TLQP-ir. increased at 30 min (∼30 %), with highest concentrations at 120 min (both: p<0.05 vs. controls), while HPLC fractions showed an increase in the TLQP-21 compatible form.

CONCLUSIONS

Upon hyperglycaemia, TLQP-21 would be released from islets, to enhance insulin secretion but we cannot exclude an autocrine activity which may regulate insulin storage/secretion.

Complement in Neurologic Disease

Classic innate immune signaling pathways provide most of the immune response in the brain. This response activates many of the canonical signaling mechanisms identified in peripheral immune cells, despite their relative absence in this immune-privileged tissue. Studies over the past decade have strongly linked complement protein production and activation to age-related functional changes and neurodegeneration. The reactivation of the complement signaling pathway in aging and disease has opened new avenues for understanding brain aging and neurological disease pathogenesis and has implicated cell types such as astrocytes, microglia, endothelial cells, oligodendrocytes, neurons, and even peripheral immune cells in these processes. In this review, we aim to unravel the past decade of research related to complement activation and its numerous consequences in aging and neurological disease.

SOX9 promotes stress-responsive transcription of VGF nerve growth factor inducible gene in renal tubular epithelial cells

Acute kidney injury (AKI) is a common clinical condition associated with diverse etiologies and abrupt loss of renal function. In patients with sepsis, rhabdomyolysis, cancer, and cardiovascular disorders, the underlying disease or associated therapeutic interventions can cause hypoxia, cytotoxicity, and inflammatory insults to renal tubular epithelial cells (RTECs), resulting in the onset of AKI. To uncover stress-responsive disease-modifying genes, here we have carried out renal transcriptome profiling in three distinct murine models of AKI. We find that Vgf nerve growth factor inducible gene up-regulation is a common transcriptional stress response in RTECs to ischemia-, cisplatin-, and rhabdomyolysis-associated renal injury. The Vgf gene encodes a secretory peptide precursor protein that has critical neuroendocrine functions; however, its role in the kidneys remains unknown. Our functional studies show that RTEC-specific Vgf gene ablation exacerbates ischemia-, cisplatin-, and rhabdomyolysis-associated AKI in vivo and cisplatin-induced RTEC cell death in vitro Importantly, aggravation of cisplatin-induced renal injury caused by Vgf gene ablation is partly reversed by TLQP-21, a Vgf-derived peptide. Finally, in vitro and in vivo mechanistic studies showed that injury-induced Vgf up-regulation in RTECs is driven by the transcriptional regulator Sox9. These findings reveal a crucial downstream target of the Sox9-directed transcriptional program and identify Vgf as a stress-responsive protective gene in kidney tubular epithelial cells.

JMV5656, a short synthetic derivative of TLQP-21, alleviates acid-induced lung injury and fibrosis in mice

TLQP-21, a peptide encoded by the prohormone VGF, is expressed in neuroendocrine cells and can modulate inflammatory processes. Since TLQP-21 can bind the complement 3a receptor 1 on macrophages, interest has risen in this peptide as a potential drug for the treatment of Acute Respiratory Distress Syndrome (ARDS), whose hospital mortality can reach 35-46%. Since no effective pharmacologic therapies are available, our aim was to exploit the potential of a short analog of TLQP-21(JMV5656) in order to modulate the inflammatory process in ARDS and the progression to pulmonary fibrosis in an experimental model of unilateral acid aspiration in mice. Mice were divided in 2 treatment groups. In the acute protocol, mice received intra-peritoneal injection of either vehicle or 0.6 mg/kg JMV5656 on experimental days 1 and 2, and ARDS was induced on day 3 under deep anesthesia by instillation of HCl (1.5 ml/kg of 0.1 M HCl in 0.9% NaCl) into the right lung; all measurements were performed 24 h later. In the subacute protocol, mice were treated as previously, but treatment with vehicle or JMV5656 was repeated also on day 4 and measurements were made 2 weeks later. Twenty-four hours after acid instillation, the total number of immune cell in the BAL rose sharply due primarily to an increase in the PMN population which increased from 1% up to 58% of total cell numbers. JMV5656 significantly reduced PMN recruitment into the alveolar space, but had no effects on cytokine levels in BAL. Two weeks after acid injury, static compliance of the right lung was significantly higher in the JMV5656-treated group compared to vehicle-treated group. Treatment with JMV5656 also blunted the acid-induced collagen deposition in the right lung. These results suggest that JMV5656 can ameliorate mechanical compliance, and reduce collagen deposition in acid-injured lungs in mice. This effect was likely due to the ability of JMV5656 to inhibit PMN recruitment in the injured lung.

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.

VGF-derived peptide TLQP-21 modulates microglial function through C3aR1 signaling pathways and reduces neuropathology in 5xFAD mice

BACKGROUND

Multiomic studies by several groups in the NIH Accelerating Medicines Partnership for Alzheimer's Disease (AMP-AD) identified VGF as a major driver of Alzheimer's disease (AD), also finding that reduced VGF levels correlate with mean amyloid plaque density, Clinical Dementia Rating (CDR) and Braak scores. VGF-derived peptide TLQP-21 activates the complement C3a receptor-1 (C3aR1), predominantly expressed in the brain on microglia. However, it is unclear how mouse or human TLQP-21, which are not identical, modulate microglial function and/or AD progression.

METHODS

We performed phagocytic/migration assays and RNA sequencing on BV2 microglial cells and primary microglia isolated from wild-type or C3aR1-null mice following treatment with TLQP-21 or C3a super agonist (C3aSA). Effects of intracerebroventricular TLQP-21 delivery were evaluated in 5xFAD mice, a mouse amyloidosis model of AD. Finally, the human HMC3 microglial cell line was treated with human TLQP-21 to determine whether specific peptide functions are conserved from mouse to human.

RESULTS

We demonstrate that TLQP-21 increases motility and phagocytic capacity in murine BV2 microglial cells, and in primary wild-type but not in C3aR1-null murine microglia, which under basal conditions have impaired phagocytic function compared to wild-type. RNA sequencing of primary microglia revealed overlapping transcriptomic changes induced by treatment with TLQP-21 or C3a super agonist (C3aSA). There were no transcriptomic changes in C3aR1-null or wild-type microglia exposed to the mutant peptide TLQP-R21A, which does not activate C3aR1. Most of the C3aSA- and TLQP-21-induced differentially expressed genes were linked to cell migration and proliferation. Intracerebroventricular TLQP-21 administration for 28 days via implanted osmotic pump resulted in a reduction of amyloid plaques and associated dystrophic neurites and restored expression of subsets of Alzheimer-associated microglial genes. Finally, we found that human TLQP-21 activates human microglia in a fashion similar to activation of murine microglia by mouse TLQP-21.

CONCLUSIONS

These data provide molecular and functional evidence suggesting that mouse and human TLQP-21 modulate microglial function, with potential implications for the progression of AD-related neuropathology.

Identification of VGF nerve growth factor inducible-producing cells in human spinal cords and expression change in patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a serious disease characterized by the degeneration of motor neurons resulting in muscle weakness and paralysis. The neuroendocrine polypeptide VGF is localized in the central nervous system and peripheral endocrine neurons and is cleaved into several polypeptides with multiple functions. Previous studies revealed that VGF was decreased in the cerebrospinal fluid of ALS model mice and sporadic ALS patients. However, it is unknown which cells supply VGF in the spinal cord and a detailed localization is lacking. In this study, we evaluated the VGF-producing cells and protein localization using in situ hybridization and immunostaining in the spinal cords of ALS and control patients. VGF mRNA was localized both in the dorsal and anterior horns of the spinal cords. Moreover, in the anterior horn, VGF mRNA co-localized with a neurofilament heavy chain, which is a motor neuron marker, and VGF mRNA-positive motor neurons were decreased in the spinal cords of ALS patients. We revealed that VGF protein level was decreased in the anterior horn of ALS patients; however, the expression level of VGF protein was not changed in the posterior horn or white matter. Furthermore, the expression level of VGF protein was conserved in ALS patients with long-term survival. These results reveal that VGF is mainly supplied by human motor neurons, and suggest that VGF expression changes may be involved in ALS pathology.

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 K_Ca3.1 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.

VGF: a biomarker and potential target for the treatment of neuropathic pain?

Supplemental Digital Content is Available in the Text.

Neuropathic pain (NP) remains an area of considerable unmet medical need. A persistent challenge in the management of NP is to target the specific mechanisms leading to a change from normal to abnormal sensory perception while ensuring that the defensive pain perception remains intact. Targeting VGF-derived neuropeptides may offer this opportunity. VGF was first identified in 1985 and is highly expressed after nerve injury and inflammation in neurons of both the peripheral and central nervous system. Subsequent studies implicate the vgf gene and its products in pain pathways. This narrative review was supported by a systematic search to identify, select, and critically appraise all relevant research investigating the role of VGF-derived neuropeptides in pain pathways. It predominantly focuses on in vivo investigations of the role of VGF in the initiation and maintenance of NP. VGF expression levels are very low under normal physiological conditions and nerve injury results in rapid and robust upregulation, increasing mechanical and thermal hypersensitivity. The identification of the 2 complement receptors with which VGF neuropeptides interact suggests a novel interplay of neuronal and immune signalling mediators. The understanding of the molecular mechanisms and signalling events by which VGF-derived active neuropeptides exert their physiological actions is in its infancy. Future work should aim to improve understanding of the downstream consequences of VGF neuropeptides thereby providing novel insights into pain mechanisms potentially leading to the identification of novel therapeutic targets.

Peptide/Receptor Co-evolution Explains the Lipolytic Function of the Neuropeptide TLQP-21

Structural and functional diversity of peptides and GPCR result from long evolutionary processes. Even small changes in sequence can alter receptor activation, affecting therapeutic efficacy. We conducted a structure-function relationship study on the neuropeptide TLQP-21, a promising target for obesity, and its complement 3a receptor (C3aR1). After having characterized the TLQP-21/C3aR1 lipolytic mechanism, a homology modeling and molecular dynamics simulation identified the TLQP-21 binding motif and C3aR1 binding site for the human (h) and mouse (m) molecules. mTLQP-21 showed enhanced binding affinity and potency for hC3aR1 compared with hTLQP-21. Consistently, mTLQP-21, but not hTLQP-21, potentiates lipolysis in human adipocytes. These findings led us to uncover five mutations in the C3aR1 binding pocket of the rodent Murinae subfamily that are causal for enhanced calculated affinity and measured potency of TLQP-21. Identifying functionally relevant peptide/receptor co-evolution mechanisms can facilitate the development of innovative pharmacotherapies for obesity and other diseases implicating GPCRs.

Photoperiodic changes in adiposity increase sensitivity of female Siberian hamsters to systemic VGF derived peptide TLQP-21

TLQP-21, a peptide encoded by the highly conserved vgf gene, is expressed in neuroendocrine cells and has been the most prominent VGF-derived peptide studied in relation to control of energy balance. The recent discovery that TLQP-21 is the natural agonist for the complement 3a receptor 1 (C3aR1) has revived interest in this peptide as a potential drug target for obesity. We have investigated its function in Siberian hamsters (Phodopus sungorus), a rodent that displays natural seasonal changes in body weight and adiposity as an adaptation to survive winter. We have previously shown that intracerebroventricular administration of TLQP-21 reduced food intake and body weight in hamsters in their long-day fat state. The aim of our current study was to determine the systemic actions of TLQP-21 on food intake, energy expenditure and body weight, and to establish whether adiposity affected these responses. Peripheral infusion of TLQP-21 (1mg/kg/day for 7 days) in lean hamsters exposed to short photoperiods (SP) reduced cumulative food intake in the home cage (p<0.05), and intake when measured in metabolic cages (P<0.01). Energy expenditure was significantly increased (p<0.001) by TLQP-21 infusion, this was associated with a significant increase in uncoupling protein 1 mRNA in brown adipose tissue (BAT) (p<0.05), and body weight was significantly reduced (p<0.05). These effects of systemic TLQP-21 treatment were not observed in hamsters exposed to long photoperiod (LP) with a fat phenotype. C3aR1 mRNA and protein were abundantly expressed in the hypothalamus, brown and white adipose tissue in hamsters, but changes in expression cannot explain the differential response to TLQP-21 in lean and fat hamsters.

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.

Neuropeptide VGF-Derived Peptide LQEQ-19 has Neuroprotective Effects in an In Vitro Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease caused by the loss of upper and lower motor neurons resulting in muscle weakness and paralysis. Recently, VGF, a neuropeptide that is a precursor of bioactive polypeptides, was found to be decreased in ALS patients, and its inducer exerted protective effects in models of ALS. These findings suggested that VGF was involved in the pathology of ALS. Here, we investigated the neuroprotective effects of various VGF-derived peptides in an in vitro ALS model. We applied seven VGF-derived peptides (TLQP-21, AQEE-30, AQEE-11, LQEQ-19, QEEL-16, LENY-13, and HVLL-7) to the motor neuron-derived cell line, NSC-34, expressing SOD1^G93A, which is one of the mutated proteins responsible for familial ALS. Nuclear staining revealed that AQEE-30 and LQEQ-19, which are derived from the C-terminal polypeptide of the VGF precursor protein, attenuated neuronal cell death. Furthermore, immunoblot analysis demonstrated that LQEQ-19 promoted the phosphorylation of Akt and extracellular signal-regulated kinase (ERK) 1/2, and inhibiting these mitogen-activated MAP kinases (MAPKs) with phosphoinositide 3-kinase or MEK/ERK inhibitors, eliminated the neuroprotective effects of LQEQ-19. In conclusion, these results suggest that VGF C-terminal peptides exert their neuroprotective effects via activation of MAPKs such as Akt and ERK1/2. Furthermore, these findings indicate that VGF-derived peptides have potential application in ALS therapy.

STIM Proteins and Orai Ca2+ Channels Are Involved in the Intracellular Pathways Activated by TLQP-21 in RAW264.7 Macrophages

TLQP-21 is a neuropeptide which has been implicated in regulation of nociception and other relevant physiologic functions. Although recent studies identified C3a and gC1q receptors as targets for TLQP-21, its intracellular molecular mechanisms of action remain largely unidentified. Our aim was (i) to explore the intracellular signaling pathway(s) activated by JMV5656, a novel derivative of TLQP-21, in RAW264.7 macrophages, and (ii) to assess linkages of these pathways with its purported receptors. JMV5656 stimulated, in a dose-dependent fashion, a rapid and transient increase in intracellular Ca²⁺ concentrations in RAW264.7 cells; repeated exposure to the peptide resulted in a lower response, suggesting a possible desensitization mechanism of the receptor. In particular, JMV5656 increased cytoplasmic Ca²⁺ levels by a PLC-dependent release of Ca²⁺ from the endoplasmic reticulum. STIM proteins and Orai Ca²⁺ channels were activated and played a crucial role. In fact, treatment of the cells with U73122 and thapsigargin modulated the increase of intracellular Ca²⁺ levels stimulated by JMV5656. Moreover, in RAW264.7 cells intracellular Ca²⁺ increases did not occur through the binding of JMV5656 to the C3a receptor, since the increase of intracellular Ca²⁺ levels induced by JMV5656 was not affected by specific siRNA against C3aR. In summary, our study provides new indications for the downstream effects of JMV5656 in macrophages, suggesting that it could activate receptors different from the C3aR.

Study of the Tissue Distribution of TLQP-21 in Mice Using [18F]JMV5763, a Radiolabeled Analog Prepared via [18F]Aluminum Fluoride Chelation Chemistry

TLQP-21 is a neuropeptide that is involved in the control of several physiological functions, including energy homeostasis. Since TLQP-21 could oppose the early phase of diet-induced obesity, it has raised a huge interest, but very little is known about its mechanisms of action on peripheral tissues. Our aim was to investigate TLQP-21 distribution in brain and peripheral tissues after systemic administration using positron emission tomography. We report here the radiolabeling of NODA-methyl phenylacetic acid (MPAA) functionalized JMV5763, a short analog of TLQP-21, with [¹⁸F]aluminum fluoride. Labeling of JMV5763 was initially performed manually, on a small scale, and then optimized and implemented on a fully automated radiosynthesis system. In the first experiment, mice were injected in the tail vein with [¹⁸F]JMV5763, and central and peripheral tissues were collected 13, 30, and 60 min after injection. Significant uptake of [¹⁸F]JMV5763 was found in stomach, intestine, kidney, liver, and adrenal gland. In the CNS, very low uptake values were measured in all tested areas, suggesting that the tracer does not efficiently cross the blood–brain barrier. Pretreatment with non-radioactive JMV5763 caused a significant reduction of tracer uptake only in stomach and intestine. In the second experiment, PET analysis was performed in vivo 10–120 min after i.v. [¹⁸F]JMV5763 administration. Results were consistent with those of the ex vivo determinations. PET images showed a progressive increase of [¹⁸F]JMV5763 uptake in intestine and stomach reaching a peak at 30 min, and decreasing at 120 min. Our results demonstrate that ¹⁸F-labeling of TLQP-21 analogs is a suitable method to study its distribution in the body.

Clearance kinetics of the VGF-derived neuropeptide TLQP-21

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, k_t, of 0.0063/min, and an initial half-life of 0.97 min with an initial clearance rate constant, k_i, 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.

CSF-1/CSF-1R axis is associated with epithelial/mesenchymal hybrid phenotype in epithelial-like inflammatory breast cancer

Inflammatory breast cancer (IBC) is a rare subtype of breast cancer, accounting for 8–10% of breast cancer-associated deaths in the US. Clinical hallmarks of IBC include tumor emboli in lymphatic vessels and E-cadherin overexpression, which supports a type of metastasis referred to as cell cluster-based metastasis, prevalent in IBC. In contrast, we previously reported epithelial-to-mesenchymal transition (EMT)-based progression of IBC, utilizing in vivo xenografts and in vitro Matrigel culture models. To address these two contradictory concepts of IBC metastasis, we used Matrigel culture to induce EMT in a panel of IBC cells. Results revealed Matrigel culture induced vimentin expression in SUM149 and SUM190 IBC cells at the transcriptional and protein levels while maintaining the expression of E-cadherin, a phenomenon referred to as partial EMT. Transcriptional profiling revealed that expression of colony-stimulating factor 1 (CSF-1) was induced in Matrigel culture. When the receptor tyrosine kinase of CSF-1 (CSF-1R) was inhibited by CSF-1R inhibitor BLZ945, the partial EMT was reversed in a dose-dependent manner, indicating that the CSF-1/CSF-1R axis plays a key role in controlling partial EMT. This observation may help reconcile the two contradictory theories of IBC metastasis, EMT vs cell cluster-based metastasis.

TLQP Peptides in Amyotrophic Lateral Sclerosis: Possible Blood Biomarkers with a Neuroprotective Role

While the VGF-derived TLQP peptides have been shown to prevent neuronal apoptosis, and to act on synaptic strengthening, their involvement in Amyotrophic Lateral Sclerosis (ALS) remains unclarified. We studied human ALS patients' plasma (taken at early to late disease stages) and primary fibroblast cultures (patients vs controls), in parallel with SOD1-G93A transgenic mice (taken at pre-, early- and late symptomatic stages) and the mouse motor neuron cell line (NSC-34) treated with Sodium Arsenite (SA) to induce oxidative stress. TLQP peptides were measured by enzyme-linked immunosorbent assay, in parallel with gel chromatography characterization, while their localization was studied by immunohistochemistry. In controls, TLQP peptides, including forms compatible with TLQP-21 and 62, were revealed in plasma and spinal cord motor neurons, as well as in fibroblasts and NSC-34 cells. TLQP peptides were reduced in ALS patients' plasma starting in the early disease stage (14% of controls) and remaining so at the late stage (16% of controls). In mice, a comparable pattern of reduction was shown (vs wild type), in both plasma and spinal cord already in the pre-symptomatic phase (about 26% and 70%, respectively). Similarly, the levels of TLQP peptides were reduced in ALS fibroblasts (31% of controls) and in the NSC-34 treated with Sodium Arsenite (53% of decrease), however, the exogeneous TLQP-21 improved cell viability (SA-treated cells with TLQP-21, vs SA-treated cells only: about 83% vs. 75%). Hence, TLQP peptides, reduced upon oxidative stress, are suggested as blood biomarkers, while TLQP-21 exerts a neuroprotective activity.

C3aR and C5aR1 act as key regulators of human and mouse β-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 β- 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 β-cell function, suggesting that low-level chronic inflammation may improve glucose homeostasis through direct effects on β-cells.

The human VGF-derived bioactive peptide TLQP-21 binds heat shock 71 kDa protein 8 (HSPA8)on the surface of SH-SY5Y cells

VGF (non-acronymic)is a secreted chromogranin/secretogranin that gives rise to a number of bioactive peptides by a complex proteolysis mechanism. VGF-derived peptides exert an extensive array of biological effects in energy metabolism, mood regulation, pain, gastric secretion function, reproduction and, perhaps, cancer. It is therefore surprising that very little is known about receptors and binding partners of VGF-derived peptides and their downstream molecular mechanisms of action. Here, using affinity chromatography and mass spectrometry-based protein identification, we have identified the heat shock cognate 71 kDa protein A8 (HSPA8)as a binding partner of human TLQP-21 on the surface of human neuroblastomaSH-SY5Y cells. Binding of TLQP-21 to membrane associated HSPA8 in live SH-SY5Y cells was further supported by cross-linking to live cells. Interaction between HSPA8 and TLQP-21 was confirmed in vitro by label-free Dynamic Mass Redistribution (DMR) studies. Furthermore, molecular modeling studies show that TLQP-21 can be docked into the HSPA8 peptide binding pocket. Identification of HSPA8 as a cell surface binding partner of TLQP-21 opens new avenues to explore the molecular mechanisms of its physiological actions, and of pharmacological modulation thereof.

Complement 3a receptor in dorsal horn microglia mediates pronociceptive neuropeptide signaling

The complement 3a receptor (C3aR1) participates in microglial signaling under pathological conditions and was recently shown to be activated by the neuropeptide TLQP-21. We previously demonstrated that TLQP-21 elicits hyperalgesia and contributes to nerve injury-induced hypersensitivity through an unknown mechanism in the spinal cord. Here we determined that this mechanism requires C3aR1 and that microglia are the cellular target for TLQP-21. We propose a novel neuroimmune signaling pathway involving TLQP-21-induced activation of microglial C3aR1 that then contributes to spinal neuroplasticity and neuropathic pain. This unique dual-ligand activation of C3aR1 by a neuropeptide (TLQP-21) and an immune mediator (C3a) represents a potential broad-spectrum mechanism throughout the CNS for integration of neuroimmune crosstalk at the molecular level.

Embryonic ablation of neuronal VGF increases energy expenditure and reduces body weight

Germline ablation of VGF, a secreted neuronal, neuroendocrine, and endocrine peptide precursor, results in lean, hypermetabolic, and infertile adult mice that are resistant to diet-, lesion-, and genetically-induced obesity and diabetes (Hahm et al., 1999, 2002). To assess whether this phenotype is predominantly driven by reduced VGF expression in developing and/or adult neurons, or in peripheral endocrine and neuroendocrine tissues, we generated and analyzed conditional VGF knockout mice, obtained by mating loxP-flanked (floxed) Vgf mice with either pan-neuronal Synapsin-Cre- or forebrain alpha-CaMKII-Cre-recombinase-expressing transgenic mice. Adult male and female mice, with conditional ablation of the Vgf gene in embryonic neurons had significantly reduced body weight, increased energy expenditure, and were resistant to diet-induced obesity. Conditional forebrain postnatal ablation of VGF in male mice, primarily in adult excitatory neurons, had no measurable effect on body weight nor on energy expenditure, but led to a modest increase in adiposity, partially overlapping the effect of AAV-Cre-mediated targeted ablation of VGF in the adult ventromedial hypothalamus and arcuate nucleus of floxed Vgf mice (Foglesong et al., 2016), and also consistent with results of icv delivery of the VGF-derived peptide TLQP-21 to adult mice, which resulted in increased energy expenditure and reduced adiposity (Bartolomucci et al., 2006). Because the lean, hypermetabolic phenotype of germline VGF knockout mice is to a great extent recapitulated in Syn-Cre^+/-,Vgf^{flpflox/flpflox} mice, we conclude that the metabolic profile of germline VGF knockout mice is largely the result of VGF ablation in embryonic CNS neurons, rather than peripheral endocrine and/or neuroendocrine cells, and that in forebrain structures such as hypothalamus, VGF and/or VGF-derived peptides play uniquely different roles in the developing and adult nervous system.

Monitoring C3aR Expression Using a Floxed tdTomato-C3aR Reporter Knock-in Mouse

C3a exerts multiple biologic functions through activation of its cognate C3a receptor. C3^-/- and C3aR^-/- mice have been instrumental in defining important roles of the C3a/C3aR axis in the regulation of acute and chronic inflammatory diseases, including ischemia/reperfusion injury, allergic asthma, autoimmune nephritis, and rheumatoid arthritis. Surprisingly little is known about C3aR expression and function in immune and stromal cells. To close this gap, we generated a floxed tandem-dye Tomato (tdTomato)-C3aR reporter knock-in mouse, which we used to monitor C3aR expression in cells residing in the lung, airways, lamina propria (LP) of the small intestine, brain, visceral adipose tissue, bone marrow (BM), spleen, and the circulation. We found a strong expression of tdTomato-C3aR in the brain, lung, LP, and visceral adipose tissue, whereas it was minor in the spleen, blood, BM, and the airways. Most macrophage and eosinophil populations were tdTomato-C3aR⁺ Interestingly, most tissue eosinophils and some macrophage populations expressed C3aR intracellularly. BM-derived dendritic cells (DCs), lung-resident cluster of differentiation (CD) 11b⁺ conventional DCs (cDCs) and monocyte-derived DCs, LP CD103⁺, and CD11b⁺ cDCs but not pulmonary CD103⁺ cDCs and splenic DCs were tdTomato-C3aR⁺ Surprisingly, neither BM, blood, lung neutrophils, nor mast cells expressed C3aR. Similarly, all lymphoid-derived cells were tdTomato-C3aR^-, except some LP-derived type 3 innate lymphoid cells. Pulmonary and LP-derived epithelial cells expressed at best minor levels of C3aR. In summary, we provide novel insights into the expression pattern of C3aR in mice. The floxed C3aR knock-in mouse will help to reliably track and conditionally delete C3aR expression in experimental models of inflammation.

A comprehensive assessment of RNA-seq protocols for degraded and low-quantity samples

BACKGROUND

RNA-sequencing (RNA-seq) has emerged as one of the most sensitive tool for gene expression analysis. Among the library preparation methods available, the standard poly(A) + enrichment provides a comprehensive, detailed, and accurate view of polyadenylated RNAs. However, on samples of suboptimal quality ribosomal RNA depletion and exon capture methods have recently been reported as better alternatives.

METHODS

We compared for the first time three commercial Illumina library preparation kits (TruSeq Stranded mRNA, TruSeq Ribo-Zero rRNA Removal, and TruSeq RNA Access) as representatives of these three different approaches using well-established human reference RNA samples from the MAQC/SEQC consortium on a wide range of input amounts (from 100 ng down to 1 ng) and degradation levels (intact, degraded, and highly degraded).

RESULTS

We assessed the accuracy of the generated expression values by comparison to gold standard TaqMan qPCR measurements and gained unprecedented insight into the limits of applicability in terms of input quantity and sample quality of each protocol. We found that each protocol generates highly reproducible results (R ² > 0.92) on intact RNA samples down to input amounts of 10 ng. For degraded RNA samples, Ribo-Zero showed clear performance advantages over the other two protocols as it generated more accurate and better reproducible gene expression results even at very low input amounts such as 1 ng and 2 ng. For highly degraded RNA samples, RNA Access performed best generating reliable data down to 5 ng input.

CONCLUSIONS

We found that the ribosomal RNA depletion protocol from Illumina works very well at amounts far below recommendation and over a good range of intact and degraded material. We also infer that the exome-capture protocol (RNA Access, Illumina) performs better than other methods on highly degraded and low amount samples.