Cellular distribution of chromogranin A in excitatory, inhibitory, aminergic and peptidergic neurons of the rodent central nervous system

Chromogranin A deficiency attenuates tauopathy by altering epinephrine-alpha-adrenergic receptor signaling in PS19 mice

Metabolic disorders such as insulin resistance and hypertension are potential risk factors for aging and neurodegenerative diseases. These conditions are reversed in Chromogranin A (CgA) knockout (CgA-KO) mice. CgA is known to be associated with protein aggregates in the brains of neurodegenerative diseases including Alzheimer's disease (AD). Here, we investigated the role of CgA in Tau pathogenesis in AD and corticobasal degeneration (CBD). CgA ablation in Tauopathy mice (PS19) (CgA-KO/PS19) reduced pathological Tau aggregation and spreading, extended lifespan, and improved cognitive function. Transcriptomic and metabolite analysis of mouse cortices revealed elevated alpha-1-adrenergic receptors (Adra1) expression and high Epinephrine (EPI) levels in PS19 mice compared to WT mice, mirroring observations in AD and CBD patients. CgA depletion in PS19 mice lowered cortical EPI levels and the expression of Adra1 back to normal. Treatment of WT hippocampal organotypic slice cultures with EPI or Adra1 agonist promoted, while an Adra1 antagonist inhibited Tau hyperphosphorylation and formation of neurofibrillary tangles, which is unaltered upon CgA depletion. These findings demonstrate the involvement of CgA in Tau pathogenesis and highlight the interplay between the EPI-Adra1 signaling pathway and CgA in Tauopathy.

Pangenome reconstruction in rats enhances genotype-phenotype mapping and variant discovery

The HXB/BXH family of recombinant inbred rat strains is a unique genetic resource that has been extensively phenotyped over 25 years, resulting in a vast dataset of quantitative molecular and physiological phenotypes. We built a pangenome graph from 10x Genomics Linked-Read data for 31 recombinant inbred rats to study genetic variation and association mapping. The pangenome includes 0.2Gb of sequence that is not present the reference mRatBN7.2, confirming the capture of substantial additional variation. We validated variants in challenging regions, including complex structural variants resolving into multiple haplotypes. Phenome-wide association analysis of validated SNPs uncovered variants associated with glucose/insulin levels and hippocampal gene expression. We propose an interaction between Pirl1l1, chromogranin expression, TNF-α levels, and insulin regulation. This study demonstrates the utility of linked-read pangenomes for comprehensive variant detection and mapping phenotypic diversity in a widely used rat genetic reference panel.

Pangenome reconstruction in rats enhances genotype-phenotype mapping and novel variant discovery

The HXB/BXH family of recombinant inbred rat strains is a unique genetic resource that has been extensively phenotyped over 25 years, resulting in a vast dataset of quantitative molecular and physiological phenotypes. We built a pangenome graph from 10x Genomics Linked-Read data for 31 recombinant inbred rats to study genetic variation and association mapping. The pangenome includes 0.2Gb of sequence that is not present the reference mRatBN7.2, confirming the capture of substantial additional variation. We validated variants in challenging regions, including complex structural variants resolving into multiple haplotypes. Phenome-wide association analysis of validated SNPs uncovered variants associated with glucose/insulin levels and hippocampal gene expression. We propose an interaction between Pirl1l1, chromogranin expression, TNF-α levels, and insulin regulation. This study demonstrates the utility of linked-read pangenomes for comprehensive variant detection and mapping phenotypic diversity in a widely used rat genetic reference panel.

Immunohistochemical field parcellation of the human hippocampus along its antero-posterior axis

The primate hippocampus includes the dentate gyrus, cornu ammonis (CA), and subiculum. CA is subdivided into four fields (CA1-CA3, plus CA3h/hilus of the dentate gyrus) with specific pyramidal cell morphology and connections. Work in non-human mammals has shown that hippocampal connectivity is precisely patterned both in the laminar and longitudinal axes. One of the main handicaps in the study of neuropathological semiology in the human hippocampus is the lack of clear laminar and longitudinal borders. The aim of this study was to explore a histochemical segmentation of the adult human hippocampus, integrating field (medio-lateral), laminar, and anteroposterior longitudinal patterning. We provide criteria for head-body-tail field and subfield parcellation of the human hippocampus based on immunodetection of Rabphilin3a (Rph3a), Purkinje-cell protein 4 (PCP4), Chromogranin A and Regulation of G protein signaling-14 (RGS-14). Notably, Rph3a and PCP4 allow to identify the border between CA3 and CA2, while Chromogranin A and RGS-14 give specific staining of CA2. We also provide novel histological data about the composition of human-specific regions of the anterior and posterior hippocampus. The data are given with stereotaxic coordinates along the longitudinal axis. This study provides novel insights for a detailed region-specific parcellation of the human hippocampus useful for human brain imaging and neuropathology.

Brain-Biomarker Changes in Body Fluids of Patients with Parkinson's Disease

Parkinson's disease (PD) is an incurable neurodegenerative disease that is rarely diagnosed at an early stage. Although the understanding of PD-related mechanisms has greatly improved over the last decade, the diagnosis of PD is still based on neurological examination through the identification of motor symptoms, including bradykinesia, rigidity, postural instability, and resting tremor. The early phase of PD is characterized by subtle symptoms with a misdiagnosis rate of approximately 16-20%. The difficulty in recognizing early PD has implications for the potential use of novel therapeutic approaches. For this reason, it is important to discover PD brain biomarkers that can indicate early dopaminergic dysfunction through their changes in body fluids, such as saliva, urine, blood, or cerebrospinal fluid (CSF). For the CFS-based test, the invasiveness of sampling is a major limitation, whereas the other body fluids are easier to obtain and could also allow population screening. Following the identification of the crucial role of alpha-synuclein (α-syn) in the pathology of PD, a very large number of studies have summarized its changes in body fluids. However, methodological problems have led to the poor diagnostic/prognostic value of this protein and alternative biomarkers are currently being investigated. The aim of this paper is therefore to summarize studies on protein biomarkers that are alternatives to α-syn, particularly those that change in nigrostriatal areas and in biofluids, with a focus on blood, and, eventually, saliva and urine.

Protein Expression of the Microglial Marker Tmem119 Decreases in Association With Morphological Changes and Location in a Mouse Model of Traumatic Brain Injury

The activation of microglia and the infiltration of macrophages are hallmarks of neuroinflammation after acute brain injuries, including traumatic brain injury (TBI). The two myeloid populations share many features in the post-injury inflammatory response, thus, being antigenically indistinguishable. Recently Tmem119, a type I transmembrane protein specifically expressed by microglia under physiological conditions, was proposed as a tool to differentiate resident microglia from blood-borne macrophages, not expressing it. However, the validity of Tmem119 as a specific marker of resident microglia in the context of acute brain injury, where microglia are activated and macrophages are recruited, needs validation. Our purpose was to investigate Tmem119 expression and distribution in relation to the morphology of brain myeloid cells present in the injured area after TBI. Mice underwent sham surgery or TBI by controlled cortical impact (CCI). Brains from sham-operated, or TBI mice, were analyzed by in situ hybridization to identify the cells expressing Tmem119, and by Western blot and quantitative immunofluorescence to measure Tmem119 protein levels in the entire brain regions and single cells. The morphology of Iba1+ myeloid cells was analyzed at different times (4 and 7 days after TBI) and several distances from the contused edge in order to associate Tmem119 expression with morphological evolution of active microglia. In situ hybridization indicated an increased Tmem119 RNA along with increased microglial complement C1q activation in the contused area and surrounding regions. On the contrary, the biochemical evaluation showed a drop in Tmem119 protein levels in the same areas. The Tmem119 immunoreactivity decreased in Iba1+ myeloid cells found in the contused cortex at both time points, with the cells showing the hypertrophic ameboid morphology having no Tmem119 expression. The Tmem119 was present on ramifications of resident microglia and its presence was decreased as a consequence of microglial activation in cortical areas close to contusion. Based on the data, we conclude that the decrease of Tmem119 in reactive microglia may depend on the process of microglial activation, which involves the retracting of their branchings to acquire an ameboid shape. The Tmem119 immunoreactivity decreases in reactive microglia to similar levels than the blood-borne macrophages, thus, failing to discriminate the two myeloid populations after TBI.

Pineal parenchymal tumor of intermediate differentiation: a systematic review and contemporary management of 389 cases reported during the last two decades

Pineal parenchymal tumor of intermediate differentiation (PPTID) is a WHO grade II and III tumor arising from pineal parenchymal cells. PPTID is a rare tumor accounting for less than 1% of all primary central nervous system neoplasms. Therefore, reports describing the clinical characteristics and biological features of PPTID are lacking. Moreover, the therapeutic strategy remains controversial. The current study aimed to evaluate treatment results and problems of contemporary therapeutic modalities of PPTID based on its features compared with other pineal parenchymal tumors. A comprehensive systematic literature review of 69 articles was performed, including articles on PPTID (389 patients) and similar tumors. Patient demographics, disease presentation, imaging characteristics, biological features, and current therapeutic options and their results were reviewed. We found that histopathological findings based on current WHO classification are well associated with survival; however, identifying and treating aggressive PPTID cases with uncommon features could be problematic. A molecular and genetic approach may help improve diagnostic accuracy. Therapeutic strategy, especially for grade III and aforementioned uncommon and aggressive tumors, remains controversial. A combination therapy involving maximum tumor resection, chemotherapy, and radiotherapy could be the first line of treatment. However, although challenging, a large prospective study would be required to identify ways to improve the clinical results of PPTID treatment.

An increase in VGF expression through a rapid, transcription-independent, autofeedback mechanism improves cognitive function

The release of neuropeptides from dense core vesicles (DCVs) modulates neuronal activity and plays a critical role in cognitive function and emotion. The granin family is considered a master regulator of DCV biogenesis and the release of DCV cargo molecules. The expression of the VGF protein (nonacronymic), a secreted neuropeptide precursor that also belongs to the extended granin family, has been previously shown to be induced in the brain by hippocampus-dependent learning, and its downregulation is mechanistically linked to neurodegenerative diseases such as Alzheimer's disease and other mood disorders. Currently, whether changes in translational efficiency of Vgf and other granin mRNAs may be associated and regulated with learning associated neural activity remains largely unknown. Here, we show that either contextual fear memory training or the administration of TLQP-62, a peptide derived from the C-terminal region of the VGF precursor, acutely increases the translation of VGF and other granin proteins, such as CgB and Scg2, via an mTOR-dependent signaling pathway in the absence of measurable increases in mRNA expression. Luciferase-based reporter assays confirmed that the 3'-untranslated region (3'UTR) of the Vgf mRNA represses VGF translation. Consistently, the truncation of the endogenous Vgf mRNA 3'UTR results in substantial increases in VGF protein expression both in cultured primary neurons and in brain tissues from knock in mice expressing a 3'UTR-truncation mutant encoded by the modified Vgf gene. Importantly, Vgf 3'UTR-truncated mice exhibit enhanced memory performance and reduced anxiety- and depression-like behaviors. Our results therefore reveal a rapid, transcription-independent induction of VGF and other granin proteins after learning that are triggered by the VGF-derived peptide TLQP-62. Our findings suggest that the rapid, positive feedforward increase in the synthesis of granin family proteins might be a general mechanism to replenish DCV cargo molecules that have been released in response to neuronal activation and is crucial for memory function and mood stability.

Stathmin-2 Mediates Glucagon Secretion From Pancreatic α-Cells

Inhibition of glucagon hypersecretion from pancreatic α-cells is an appealing strategy for the treatment of diabetes. Our hypothesis is that proteins that associate with glucagon within alpha cell secretory granules will regulate glucagon secretion, and may provide druggable targets for controlling abnormal glucagon secretion in diabetes. Recently, we identified a dynamic glucagon interactome within the secretory granules of the α cell line, αTC1-6, and showed that select proteins within the interactome could modulate glucagon secretion. In the present study, we show that one of these interactome proteins, the neuronal protein stathmin-2, is expressed in αTC1-6 cells and in mouse pancreatic alpha cells, and is a novel regulator of glucagon secretion. The secretion of both glucagon and Stmn2 was significantly enhanced in response to 55 mM K⁺, and immunofluorescence confocal microscopy showed co-localization of stathmin-2 with glucagon and the secretory granule markers chromogranin A and VAMP-2 in αTC1-6 cells. In mouse pancreatic islets, Stathmin-2 co-localized with glucagon, but not with insulin, and co-localized with secretory pathway markers. To show a function for stathmin-2 in regulating glucagon secretion, we showed that siRNA-mediated depletion of stathmin-2 in αTC1-6 cells caused glucagon secretion to become constitutive without any effect on proglucagon mRNA levels, while overexpression of stathmin-2 completely abolished both basal and K⁺-stimulated glucagon secretion. Overexpression of stathmin-2 increased the localization of glucagon into the endosomal-lysosomal compartment, while depletion of stathmin-2 reduced the endosomal localization of glucagon. Therefore, we describe stathmin-2 as having a novel role as an alpha cell secretory granule protein that modulates glucagon secretion via trafficking through the endosomal-lysosomal system. These findings describe a potential new pathway for the regulation of glucagon secretion, and may have implications for controlling glucagon hypersecretion in diabetes.

Pituitary Adenylate Cyclase-Activating Peptide (PACAP)-Glutamate Co-transmission Drives Circadian Phase-Advancing Responses to Intrinsically Photosensitive Retinal Ganglion Cell Projections by Suprachiasmatic Nucleus

Results from a variety of sources indicate a role for pituitary adenylate cyclase-activating polypeptide (PACAP) in light/glutamate-induced phase resetting of the circadian clock mediated by the retinohypothalamic tract (RHT). Attempts to block or remove PACAP’s contribution to clock-resetting have generated phenotypes that differ in their responses to light or glutamate. For example, previous studies of circadian behaviors found that period-maintenance and early-night phase delays are intact in PACAP-null mice, yet there is a consistent deficit in behavioral phase-resetting to light stimulation in the late night. Here we report rodent stimulus–response characteristics of PACAP release from the RHT, and map these to responses of the suprachiasmatic nucleus (SCN) in intact and PACAP-deficient mouse hypothalamus with regard to phase-resetting. SCN of PACAP-null mice exhibit normal circadian rhythms in neuronal activity, but are “blind” to glutamate stimulating phase-advance responses in late night, although not in early night, consistent with previously reported selective lack of late-night light behavioral responsiveness of these mice. Induction of CREB phosphorylation, a hallmark of the light/glutamate response of the SCN, also is absent in SCN-containing ex vivo slices from PACAP-deficient mouse hypothalamus. PACAP replacement to the SCN of PACAP-null mice restored wild-type phase-shifting of firing-rate patterns in response to glutamate applied to the SCN in late night. Likewise, ex vivo SCN of wild-type mice post-orbital enucleation are unresponsive to glutamate unless PACAP also is restored. Furthermore, we demonstrate that the period of efficacy of PACAP at SCN nerve terminals corresponds to waxing of PACAP mRNA expression in ipRGCs during the night, and waning during the day. These results validate the use of PACAP-deficient mice in defining the role and specificity of PACAP as a co-transmitter with glutamate in ipRGC-RHT projections to SCN in phase advancing the SCN circadian rhythm in late night.

Chromogranin A and its fragments in cardiovascular, immunometabolic, and cancer regulation

Chromogranin A (CgA)-the index member of the chromogranin/secretogranin secretory protein family-is ubiquitously distributed in endocrine, neuroendocrine, and immune cells. Elevated levels of CgA-related polypeptides, consisting of full-length molecules and fragments, are detected in the blood of patients suffering from neuroendocrine tumors, heart failure, renal failure, hypertension, rheumatoid arthritis, and inflammatory bowel disease. Full-length CgA and various CgA-derived peptides, including vasostatin-1, pancreastatin, catestatin, and serpinin, are expressed at different relative levels in normal and pathological conditions and exert diverse, and sometime opposite, biological functions. For example, CgA is overexpressed in genetic hypertension, whereas catestatin is diminished. In rodents, the administration of catestatin decreases hypertension, cardiac contractility, obesity, atherosclerosis, and inflammation, and it improves insulin sensitivity. By contrast, pancreastatin is elevated in diabetic patients, and the administration of this peptide to obese mice decreases insulin sensitivity and increases inflammation. CgA and the N-terminal fragment of vasostatin-1 can enhance the endothelial barrier function, exert antiangiogenic effects, and inhibit tumor growth in animal models, whereas CgA fragments lacking the CgA C-terminal region promote angiogenesis and tumor growth. Overall, the CgA system, consisting of full-length CgA and its fragments, is emerging as an important and complex player in cardiovascular, immunometabolic, and cancer regulation.

Evaluating the Effects of Various Decalcification Protocols on Immunohistochemical Staining in Zebrafish (Danio rerio)

Fixation and decalcification can alter protein structure in tissues, influencing the efficacy of primary antibodies routinely used in immunohistochemical (IHC) staining. Histologic examination of zebrafish requires both processes, making staining and analysis potentially challenging. Here, we investigated the effects of common fixation and decalcification protocols on IHC staining in zebrafish. We also identified zebrafish-reactive and -specific antibodies for use in research and diagnostics. For several of the antibodies, time spent in Dietrich's fixative containing 2% glacial acetic acid or 3.4% formaldehyde followed by decalcification with ethylenediaminetetraacetic acid (EDTA) significantly impacted IHC staining quality, particularly regarding staining intensity. Protocols utilizing shorter fixation times produced higher-quality stains. In addition, individual markers were variably affected by the type of fixative. Dietrich's fixative significantly reduced staining quality for the "neural" markers: glial fibrillar acidic protein, chromogranin A, S100. A negative time-dependent effect of fixation on staining quality was found for several antibodies: muscle actin (Dietrich's only), cytokeratin AE1/AE3, chromogranin, and S100. Neither decalcification protocol had a statistically significant negative time-dependent effect on staining quality. Based on our results, we suggest shorter fixation and decalcification protocols to best preserve IHC staining quality as well as recommend deliberate selection of the fixative used depending on the protein of interest.

ATM and ATR play complementary roles in the behavior of excitatory and inhibitory vesicle populations

ATM (ataxia-telangiectasia mutated) and ATR (ATM and Rad3-related) are large PI3 kinases whose human mutations result in complex syndromes that include a compromised DNA damage response (DDR) and prominent nervous system phenotypes. Both proteins are nuclear-localized in keeping with their DDR functions, yet both are also found in cytoplasm, including on neuronal synaptic vesicles. In ATM- or ATR-deficient neurons, spontaneous vesicle release is reduced, but a drop in ATM or ATR level also slows FM4-64 dye uptake. In keeping with this, both proteins bind to AP-2 complex components as well as to clathrin, suggesting roles in endocytosis and vesicle recycling. The two proteins play complementary roles in the DDR; ATM is engaged in the repair of double-strand breaks, while ATR deals mainly with single-strand damage. Unexpectedly, this complementarity extends to these proteins' synaptic function as well. Superresolution microscopy and coimmunoprecipitation reveal that ATM associates exclusively with excitatory (VGLUT1⁺) vesicles, while ATR associates only with inhibitory (VGAT⁺) vesicles. The levels of ATM and ATR respond to each other; when ATM is deficient, ATR levels rise, and vice versa. Finally, blocking NMDA, but not GABA, receptors causes ATM levels to rise while ATR levels respond to GABA, but not NMDA, receptor blockade. Taken together, our data suggest that ATM and ATR are part of the cellular "infrastructure" that maintains the excitatory/inhibitory balance of the nervous system. This idea has important implications for the human diseases resulting from their genetic deficiency.

Activation of the HPA axis and depression of feeding behavior induced by restraint stress are separately regulated by PACAPergic neurotransmission in the mouse

We measured serum CORT elevation in wild-type and PACAP-deficient C57BL/6N male mice after acute (1 h) or prolonged (2-3 h) daily restraint stress for 7 d. The PACAP dependence of CORT elevation was compared to that of stress-induced hypophagia. Daily restraint induced unhabituated peak CORT elevation, and hypophagia/weight loss, of similar magnitude for 1, 2, and 3 h of daily restraint, in wild-type mice. Peak CORT elevation, and hypophagia, were both attenuated in PACAP-deficient mice for 2 and 3 h daily restraint. Hypophagia induced by 1-h daily restraint was also greatly reduced in PACAP-deficient mice, however CORT elevation, both peak and during recovery from stress, was unaffected. Thus, hypothalamic PACAPergic neurotransmission appears to affect CRH gene transcription and peptide production, but not CRH release, in response to psychogenic stress. A single exposure to restraint sufficed to trigger hypophagia over the following 24 h. PACAP deficiency attenuated HPA axis response (CORT elevation) to prolonged (3 h) but not acute (1 h) single-exposure restraint stress, while hypophagia induced by either a single 1 h or a single 3 h restraint were both abolished in PACAP-deficient mice. These results suggest that PACAP's actions to promote suppression of food intake following an episode of psychogenic stress is unrelated to the release of CRH into the portal circulation to activate the pituitary-adrenal axis. Furthermore, demonstration of suppressed food intake after a single 1-h restraint stress provides a convenient assay for investigating the location of the synapses and circuits mediating the effects of PACAP on the behavioral sequelae of psychogenic stress.

The extended granin family: structure, function, and biomedical implications

The chromogranins (chromogranin A and chromogranin B), secretogranins (secretogranin II and secretogranin III), and additional related proteins (7B2, NESP55, proSAAS, and VGF) that together comprise the granin family subserve essential roles in the regulated secretory pathway that is responsible for controlled delivery of peptides, hormones, neurotransmitters, and growth factors. Here we review the structure and function of granins and granin-derived peptides and expansive new genetic evidence, including recent single-nucleotide polymorphism mapping, genomic sequence comparisons, and analysis of transgenic and knockout mice, which together support an important and evolutionarily conserved role for these proteins in large dense-core vesicle biogenesis and regulated secretion. Recent data further indicate that their processed peptides function prominently in metabolic and glucose homeostasis, emotional behavior, pain pathways, and blood pressure modulation, suggesting future utility of granins and granin-derived peptides as novel disease biomarkers.