Profiles of VGF Peptides in the Rat Brain and Their Modulations after Phencyclidine Treatment

Abstract

From the VGF precursor protein originate several low molecular weight peptides, whose distribution in the brain and blood circulation is not entirely known. Among the VGF peptides, those containing the N-terminus portion were altered in the cerebro-spinal fluid (CSF) and hypothalamus of schizophrenia patients. “Hence, we aimed to better investigate the involvement of the VGF peptides in schizophrenia by studying their localization in the brain regions relevant for the disease, and revealing their possible modulations in response to certain neuronal alterations occurring in schizophrenia”. We produced antibodies against different VGF peptides encompassing the N-terminus, but also C-terminus-, TLQP-, GGGE- peptide sequences, and the so named NERP-3 and -4. These antibodies were used to carry out specific ELISA and immunolocalization studies while mass spectrometry (MS) analysis was also performed to recognize the intact brain VGF fragments. We used a schizophrenia rat model, in which alterations in the prepulse inhibition (PPI) of the acoustic startle response occurred after PCP treatment. In normal rats, all the VGF peptides studied were distributed in the brain areas examined including hypothalamus, prefrontal cortex, hippocampus, accumbens and amygdaloid nuclei and also in the plasma. By liquid chromatography-high resolution mass, we identified different intact VGF peptide fragments, including those encompassing the N-terminus and the NERPs. PCP treatment caused behavioral changes that closely mimic schizophrenia, estimated by us as a disruption of PPI of the acoustic startle response. The PCP treatment also induced selective changes in the VGF peptide levels within certain brain areas. Indeed, an increase in VGF C-terminus and TLQP peptides was revealed in the prefrontal cortex (p < 0.01) where they were localized within parvoalbumin and tyrosine hydroxylase (TH) containing neurons, respectively. Conversely, in the nucleus accumbens, PCP treatment produced a down-regulation in the levels of VGF C-terminus-, N-terminus- and GGGE- peptides (p < 0.01), expressed in GABAergic- (C-terminus/GGGE) and somatostatin- (N-terminus) neurons. These results confirm that VGF peptides are widely distributed in the brain and modulated in specific areas involved in schizophrenia.

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

“…Compared to other VGF-derived peptides, TLQP peptides expression is low in the brain, mainly restricted to the hypothalamus, in a subpopulation of neurons projecting to a discrete areas of median eminence, in the prefrontal cortex, and in the limbic region [18], whilst are more represented in hypothalamic-pituitary axis, plasma, as well as in several peripheral locations [19,20]. The tissue distribution of TLQP-21 was recently explored by studies performed with a radiolabeled fluorine- 18 [18F] short analog of TLQP-21, administered intravenously (i.v.) in mice and analyzed by PET imaging [21].…”

“…Upon VGF cleavage by prohormone convertase (PC) 1/3 and PC2, a variety of bioactive peptides of low molecular weight are generated [13]; they are stored in dense core secretory vesicles and secreted upon stimuli [15]. More than 10 different VGF-derived peptides were detected in rat brain, bovine pituitary and human cerebrospinal fluid (CSF) [16][17][18]. Among them, those endowed with specific neuronal activities are: (i) neuroendocrine regulatory peptides-1 and -2 (NERP-1 and NERP-2); (ii) NAPP-129, also called VGF 20, based on its molecular weight (20 kDa); (iii) TLQP-62 (also known as VGF 10, 10 kDa) and TLQP-21; (iv) HHPD-41; (v) AQEE-30 (or Peptide V) and AQEE-11; vi) and LQEQ-19.…”

“…Although C3aR1 has been proposed as the putative receptor for TLQP-21 [71], some data argue against this hypothesis. In RAW264.7 cells that express C3aR1, the mobilization of intracellular Ca 2+ can be induced by stimulation with C3a, the natural ligand of C3aR1, and C3a (70)(71)(72)(73)(74)(75)(76)(77) peptide, an active fragment of C3a, as well as with TLQP-21 and JMV5656, a novel short analogue of TLQP-21 (TLQP-21 [9][10][11][12][13][14][15][16][17][18][19][20][21] [68]. However, in the same cells, the existence of two different receptors could be suggested by the following results: 1) repeated administration of JMV5656 induced a progressive reduction of Ca 2+ release elicited by subsequent stimulations with JMV5656, a likely index of homologous receptor desensitization; 2) repeated C3a (70−77) stimulations, instead, consistently elicited full intracellular Ca 2+ responses; 3) the use of siRNAs against C3aR decreased intracellular Ca 2+ mobilization stimulated by C3a but not JMV5656 [68].…”

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

“…The guinea-pig primary antiserum to TLQP peptides, specific for their common Nterminal portion, previously described in detail (Brancia et al, 2005) was extensively used in different organs and tissues (Cocco et al, 2007Brancia C et al, 2010;Noli et al, 2014;D'Amato et al, 2015;Noli et al, 2017). Briefly, a synthetic peptide corresponding to rat VGF 556-564 , with the addition of a C-terminal cysteine residue, was conjugated via its C-terminus to keyhole limpet hemocyanin (KLH), and used for immunizations.…”

“…Moreover, since the Sardinian population has a high predominance of TARDBP mutation (Chiò et al, 2011), as reflected in our cohort of patients, we were not able to study any correlation between TLQP levels and specific ALS mutation/s. While future studies will be done by us to investigate if the reduction of TLQP peptides is peculiar for ALS, schizophrenia induced by phencyclidine has not produced any TLQP changes in the rat blood (Noli et al, 2017).…”