The psychiatric risk gene BRD1 modulates mitochondrial bioenergetics by transcriptional regulation.

Bromodomain containing 1 (BRD1) encodes an epigenetic regulator that controls the expression of genetic networks linked to mental illness. BRD1 is essential for normal brain development and its role in psychopathology has been demonstrated in genetic and preclinical studies. However, the neurobiology that bridges its molecular and neuropathological effects remains poorly explored. Here, using publicly available datasets, we find that BRD1 targets nuclear genes encoding mitochondrial proteins in cell lines and that modulation of BRD1 expression, irrespective of whether it is downregulation or upregulation of one or the other existing BRD1 isoforms (BRD1-L and BRD1-S), leads to distinct shifts in the expression profile of these genes. We further show that the expression of nuclear genes encoding mitochondrial proteins is negatively correlated with the expression of BRD1 mRNA during human brain development. In accordance, we identify the key gate-keeper of mitochondrial metabolism, Peroxisome proliferator-activated receptor (PPAR) among BRD1's co-transcription factors and provide evidence that BRD1 acts as a co-repressor of PPAR-mediated transcription. Lastly, when using quantitative PCR, mitochondria-targeted fluorescent probes, and the Seahorse XFe96 Analyzer, we demonstrate that modulation of BRD1 expression in cell lines alters mitochondrial physiology (mtDNA content and mitochondrial mass), metabolism (reducing power), and bioenergetics (among others, basal, maximal, and spare respiration) in an expression level- and isoform-dependent manner. Collectively, our data suggest that BRD1 is a transcriptional regulator of nuclear-encoded mitochondrial proteins and that disruption of BRD1's genomic actions alters mitochondrial functions. This may be the mechanism underlying the cellular and atrophic changes of neurons previously associated with BRD1 deficiency and suggests that mitochondrial dysfunction may be a possible link between genetic variation in BRD1 and psychopathology in humans.

Characterization of erenumab and rimegepant on calcitonin gene-related peptide induced responses in Xenopus Laevis oocytes expressing the calcitonin gene-related peptide receptor and the amylin-1 receptor.

BACKGROUND: The clinical use of calcitonin gene-related peptide receptor (CGRP-R) antagonists and monoclonal antibodies against CGRP and CGRP-R has offered new treatment possibilities for migraine patients. CGRP activates both the CGRP-R and structurally related amylin 1 receptor (AMY1-R). The relative effect of erenumab and the small-molecule CGRP-R antagonist, rimegepant, towards the CGRP-R and AMY-R needs to be further characterized. METHODS: The effect of CGRP and two CGRP-R antagonists were examined in Xenopus laevis oocytes expressing human CGRP-R, human AMY1-R and their subunits. RESULTS: CGRP administered to receptor expressing oocytes induced a concentration-dependent increase in current with the order of potency CGRP-R> > AMY1-R > calcitonin receptor (CTR). There was no effect on single components of the CGRP-R; calcitonin receptor-like receptor and receptor activity-modifying protein 1. Amylin was only effective on AMY1-R and CTR. Inhibition potencies (pIC50 values) for erenumab on CGRP induced currents were 10.86 and 9.35 for CGRP-R and AMY1-R, respectively. Rimegepant inhibited CGRP induced currents with pIC50 values of 11.30 and 9.91 for CGRP-R and AMY1-R, respectively. CONCLUSION: Our results demonstrate that erenumab and rimegepant are potent antagonists of CGRP-R and AMY1-R with 32- and 25-times preference for the CGRP-R over the AMY1-R, respectively. It is discussed if this difference in affinity between the two receptors is the likely reason why constipation is a common and serious adverse effect during CGRP-R antagonism but less so with CGRP binding antibodies.

CGRP-dependent signalling pathways involved in mouse models of GTN- cilostazol- and levcromakalim-induced migraine.

BACKGROUND: Knowledge of exact signalling events during migraine attacks is lacking. Various substances are known to trigger migraine attacks in patients and calcitonin gene-related peptide antagonising drugs are effective against migraine pain. Here, we investigated the signalling pathways involved in three different mouse models of provoked migraine and relate them to calcitonin gene-related peptide and other migraine-relevant targets. METHODS: In vivo mouse models of glyceryl trinitrate-, cilostazol- and levcromakalim-induced migraine were applied utilising tactile sensitivity to von Frey filaments as measuring readout. Signalling pathways involved in the three models were dissected by use of specific knockout mice and chemical inhibitors. In vivo results were supported by ex vivo wire myograph experiments measuring arterial dilatory responses and ex vivo calcitonin gene-related peptide release from trigeminal ganglion and trigeminal nucleus caudalis from mice. RESULTS: Glyceryl trinitrate-induced hypersensitivity was dependent on both prostaglandins and transient receptor potential cation channel, subfamily A, member 1, whereas cilostazol- and levcromakalim-induced hypersensitivity were independent of both. All three migraine triggers activated calcitonin gene-related peptide signalling, as both receptor antagonism and antibody neutralisation of calcitonin gene-related peptide were effective inhibitors of hypersensitivity in all three models. Stimulation of trigeminal ganglia and brain stem tissue samples with cilostazol and levcromakalim did not result in release of calcitonin gene-related peptide, and vasodilation following levcromakalim stimulation was independent of CGRP receptor antagonism. CONCLUSION: The mouse models of glyceryl trinitrate-, cilostazol- and levcromakalim- induced migraine all involve calcitonin gene-related peptide signalling in a complex interplay between different cell/tissue types. These models are useful in the study of migraine mechanisms.

Abnormal Amyloid Load in Mild Cognitive Impairment: The Effect of Reducing the PiB-PET Threshold.

BACKGROUND AND PURPOSE: In vivo detection of ß-amyloid (Aß) plaques in Alzheimer's disease (AD) is now possible with 11 C-PiB positron emission tomography (PET). Conventionally, a cortical:cerebellar PiB uptake ratio threshold of 1.4-1.5 has been used to categorize at-risk subjects as "amyloid-positive" and "amyloid-negative." It has been suggested that this threshold is too conservative and may miss early amyloid pathology. We investigated the relationship between conventional and lower baseline 11 C-PiB PET thresholds for raised amyloid load and the subsequent clinical and radiological progression of mild cognitive impairment (MCI) cases longitudinally. METHODS: We serially determined the cortical amyloid load with 11 C-PiB PET of 44 MCI subjects over 2 years and compared findings with those for 12 healthy controls (HC) and 5 AD cases. RESULTS: Twenty-four subjects were classified as normal at baseline with mean cortical PiB standard uptake value ratios (SUVR) between 1.2 and 1.5. Their cognitive status remained stable over time. Three of these cases increased their amyloid load above a threshold of 1.5 over 2 years. Twenty-seven "raised amyloid" MCI cases with baseline cortical SUVRs above 1.5, showed deteriorating cognition. Note that 50% of these cases converted clinically to AD during the follow-up period. CONCLUSION: Use of a PiB SUVR threshold of >1.5 for raised amyloid missed 14.3% of MCI cases who likely had Thal stage 1 or 2 pathology and showed a progressive amyloid increase over 2 years. Lowering the threshold for abnormality to 1.3 abolished all false negatives but resulted in 75% of HCs being falsely diagnosed as raised amyloid subjects.

PACAP-38 and PACAP(6-38) Degranulate Rat Meningeal Mast Cells via the Orphan MrgB3-Receptor.

Infusion of pituitary adenylate cyclase activating peptide-38 (PACAP-38) provokes migraine attacks in migraineurs and headache in non-migraineurs. Adverse events like long-lasting flushing and heat sensation can be terminated with oral antihistamine treatment, indicating the involvement of mast cell activation after PACAP-infusion. Degranulation of rat peritoneal mast cells was provoked by several isoforms of PACAP via previously unknown receptor pharmacology. The effect might thus be mediated either via specific splice variants of the PAC1-receptor or via an unknown receptor for PACAP-38. In the present study, we characterize degranulation of rat meningeal mast cells in response to PACAP-receptor ligands. Furthermore, we investigate if PACAP-38-induced mast cell degranulation is mediated via PAC1-receptor splice variants and/or via the orphan Mas-related G-protein coupled member B3 (MrgB3)-receptor. To address this, the pharmacological effect of different PACAP isoforms on meningeal mast cell degranulation was investigated in the hemisected skull model after toluidine blue staining followed by microscopic quantification. Presence of mRNA encoding PAC1-receptor splice variants and the MrgB3-receptor in rat mast cells was investigated by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis. The effect of PACAP isoforms on PAC1- and MrgB3-receptor-expressing Xenopus laevis oocytes were performed by two-electrode voltage-clamp (TEVC) electrophysiology. PACAP-38 is a more potent mast cell degranulating agent than Pituitary Adenylate Cyclase Activating Peptide-27 (PACAP-27) in the meninges. Presence of mRNA encoding the PAC1-receptor and its different splice variants could not be detected in peritoneal mast cells by RT-PCR, whereas the orphan MrgB3-receptor, recently suggested to be a mediator of basic secretagogues-induced mast cell degranulation, was widely present. In PAC1-receptor-expressing Xenopus laevis oocytes both PACAP-38, PACAP-27 and the specific PAC1-receptor agonist maxadilan were equipotent, however, only PACAP-38 showed a significant degranulatory effect on mast cells. We confirmed Pituitary Adenylate Cyclase Activating Peptide(6-38) [PACAP(6-38)] to be a PAC1-receptor antagonist, and we demonstrated that it is a potent mast cell degranulator and have an agonistic effect on MrgB3-receptors expressed in oocytes. The present study provides evidence that PACAP-induced mast cell degranulation in rat is mediated through a putative new PACAP-receptor with the order of potency being: PACAP-38 = PACAP(6-38) > > PACAP-27 = maxadilan. The results suggest that the observed responses are mediated via the orphan MrgB3-receptor.