CP55940-induced vasorelaxation is endothelial-dependent and mediated by the CB1R through NOS, COX and EDHF pathways in porcine cerebral arteries.

Using swine as an experimental model, we examined whether the cannabinoid receptors (CB1R and CB2R) modulated vasomotor tone in isolated pial arteries. It was hypothesized that the CB1R would mediate cerebral artery vasorelaxation in an endothelial-dependent manner. First-order pial arteries were isolated from female Landrace pigs (age = 2 months; N = 27) for wire and pressure myography. Arteries were pre-contracted with a thromboxane A2 analogue (U-46619) and vasorelaxation in response to the CB1R and CB2R receptor agonist CP55940 was examined in the following conditions: 1) untreated; 2) inhibition of the CB1R (AM251); or 3) inhibition of the CB2R receptor (AM630). The data revealed that CP55940 elicits a CB1R-dependent relaxation in pial arteries. CB1R expression was confirmed using immunoblot and immunohistochemical analyses. Subsequently, the role of different endothelial-dependent pathways in the CB1R-mediated vasorelaxation was examined using: 1) denudation (removal of the endothelium); 2) inhibition of cyclooxygenase (COX; Naproxen); 3) inhibition of nitric oxide synthase (NOS; L-NAME); and 4) combined inhibition of COX + NOS. The data revealed CB1R-mediated vasorelaxation was endothelial-dependent, with contributions from COX-derived prostaglandins, NO, and endothelium-dependent hyperpolarizing factor (EDHF). Pressurized arteries underwent myogenic curves (20-100 mmHg) under the following conditions: 1) untreated; 2) inhibition of the CB1R. The data revealed CB1R inhibition increased basal myogenic tone, but not myogenic reactivity. As the vascular responses were assessed in isolated pial arteries, this work reveals that the CB1R modulates cerebrovascular tone independently of changes in brain metabolism.

Detecting Monoamine Oxidase A and B Proteins: A Western Blotting Protocol and Some Practical Considerations.

The expression of the two isoforms of monoamine oxidase (MAO A and MAO B) is often inferred from proxy measures such as mRNA transcript levels or catalytic activity. Yet the literature is clear that the proportionality of protein, mRNA, and activity does not guarantee that any of these measures can be used as a proxy for any of the others. Here we provide a protocol for the detection of MAO proteins in cell lysates that can be adapted readily to tissue preparations. Given that MAOs influence many physiological and pathological processes, we feel it is essential to include measures of protein expression when exploring genetic regulation or catalytic properties of these important enzymes.

An (Immuno) Fluorescence Protocol for Monitoring Monoamine Oxidase A/B Protein Distribution Within the Cell.

The influence of a protein is not determined exclusively by its level of expression, but also by its localization within the cell. The literature often refers to the enzyme monoamine oxidase (MAO) as a mitochondrial enzyme, yet there is evidence that mitochondria-independent pools of MAO exist. These pools of MAO could exert distinct influences across physiological as well as pathological phenotypes. Fluorescence microscopy is a powerful tool for spatially resolving target proteins in cell and tissue preparations. This can rely on an antibody-based probe that targets the endogenous protein, e.g., immunofluorescence. In the event that antibodies might not be readily available or if one is interested in characterizing a variant of the wild-type protein, then a recombinant protein with a fluorescent fusion "tag" is preferred. We now describe a protocol for the detection of endogenous MAO using indirect immunofluorescence and a version of the protocol with minor modification for detecting (green) fluorescent protein-tagged MAOs. One observation we can highlight using these easily adaptable approaches is that MAO A and MAO B do not follow similar patterns of distribution throughout the cell, suggesting potential expression of MAO A and MAO B on distinct pools of mitochondria. Furthermore, distinct subcellular compartmentalization is suggested by the fact that a pool of MAO A, but not MAO B, is associated with certain lysosomal compartments. However, directed and quantitative studies will be required before any definitive statement can be made on these intriguing possibilities.

The Aß(1-38) peptide is a negative regulator of the Aß(1-42) peptide implicated in Alzheimer disease progression.

The pool of ß-Amyloid (Aß) length variants detected in preclinical and clinical Alzheimer disease (AD) samples suggests a diversity of roles for Aß peptides. We examined how a naturally occurring variant, e.g. Aß(1-38), interacts with the AD-related variant, Aß(1-42), and the predominant physiological variant, Aß(1-40). Atomic force microscopy, Thioflavin T fluorescence, circular dichroism, dynamic light scattering, and surface plasmon resonance reveal that Aß(1-38) interacts differently with Aß(1-40) and Aß(1-42) and, in general, Aß(1-38) interferes with the conversion of Aß(1-42) to a ß-sheet-rich aggregate. Functionally, Aß(1-38) reverses the negative impact of Aß(1-42) on long-term potentiation in acute hippocampal slices and on membrane conductance in primary neurons, and mitigates an Aß(1-42) phenotype in Caenorhabditis elegans. Aß(1-38) also reverses any loss of MTT conversion induced by Aß(1-40) and Aß(1-42) in HT-22 hippocampal neurons and APOE ε4-positive human fibroblasts, although the combination of Aß(1-38) and Aß(1-42) inhibits MTT conversion in APOE ε4-negative fibroblasts. A greater ratio of soluble Aß(1-42)/Aß(1-38) [and Aß(1-42)/Aß(1-40)] in autopsied brain extracts correlates with an earlier age-at-death in males (but not females) with a diagnosis of AD. These results suggest that Aß(1-38) is capable of physically counteracting, potentially in a sex-dependent manner, the neuropathological effects of the AD-relevant Aß(1-42).

Age- and sex-dependent profiles of APP fragments and key secretases align with changes in despair-like behavior and cognition in young APPSwe/Ind mice.

Biological sex exerts distinct influences on brain levels of the ß-amyloid (Aß) peptide in both clinical depression and Alzheimer disease (AD), yet studies in animal models focus primarily on males. We examined behavioral 'despair'/depression (using the tail-suspension test) and memory (using the novel object recognition task) in J20 (hAPPSwe/Ind) mice. Three month-old male (but not female) J20 mice exhibited less despair-like behavior, but more evidence of cognitive deficits. In young J20 mice, only soluble Aß peptides -primarily Aß(1-40)- were detected. There was no evidence of an effect on despair-like behavior in the six month-old J20 mice, although cognitive deficits were now evident in both sexes, and coincided with a greater proportion of the neurotoxic Aß(1-42) species (in soluble as well as insoluble fractions). This age-dependent shift in Aß peptide profile coincided with reduced expression of glycosylated species of ADAM-10 (α-secretase) and BACE1 (ß-secretase), and an increased co-immunoprecipitation of presenilin-1 with nicastrin (components of the γ-secretase complex). Sex-dependent changes in depression-related monoaminergic, e.g. serotonin and dopamine (but not noradrenaline), systems were evident already in young J20 mice. It is critical to acknowledge that sex-dependent APP-related phenotypes might differentially influence modifiable depression-related monoaminergic signalling at some of the earliest pathological stages of clinical AD.

Glycosylation States of Pre- and Post-synaptic Markers of 5-HT Neurons Differ With Sex and 5-HTTLPR Genotype in Cortical Autopsy Samples.

The serotonin (5-hydroxytryptamine, 5-HT) transporter (5-HTT) gene-linked polymorphic region (5-HTTLPR) is thought to alter 5-HT signaling and contribute to behavioral and cognitive phenotypes in depression as well as Alzheimer disease (AD). We explored how well the short (S) and long (L) alleles of the 5-HTTLPR align with serotoninergic indices in 60 autopsied cortical samples from early-onset AD/EOAD and late-onset AD/LOAD donors, and age- and sex-matched controls. Stratifying data by either diagnosis-by-genotype or by sex-by-genotype revealed that the donor's 5-HTTLPR genotype, i.e., L/L, S/L, or S/S, did not affect 5-HTT mRNA or protein expression. However, the glycosylation of 5-HTT was significantly higher in control female (vs. male) samples and tended to decrease in female EOAD/LOAD samples, but remained unaltered in male LOAD samples. Glycosylated forms of the vesicular monoamine transporter (VMAT2) were lower in both male and female AD samples, while a sex-by-genotype stratification revealed a loss of VMAT2 glycosylation specifically in females with an L/L genotype. VMAT2 and 5-HTT glycosylation were correlated in male samples and inversely correlated in female samples in both stratification models. The S/S genotype aligned with lower levels of 5-HT turnover in females (but not males) and with an increased glycosylation of the post-synaptic 5-HT2C receptor. Interestingly, the changes in presynaptic glycosylation were evident primarily in female carriers of the APOE ε4 risk factor for AD. Our data do not support an association between 5-HTTLPR genotype and 5-HTT expression, but they do reveal a non-canonical association of 5-HTTLPR genotype with sex-dependent glycosylation changes in pre- and post-synaptic markers of serotoninergic neurons. These patterns of change suggest adaptive responses in 5-HT signaling and could certainly be contributing to the female prevalence in risk for either depression or AD.

Alzheimer Disease and Selected Risk Factors Disrupt a Co-regulation of Monoamine Oxidase-A/B in the Hippocampus, but Not in the Cortex.

Monoamine oxidase-A (MAO-A) and MAO-B have both been implicated in the pathology of Alzheimer disease (AD). We examined 60 autopsied control and AD donor brain samples to determine how well MAO function aligned with two major risk factors for AD, namely sex and APOE ε4 status. MAO-A activity was increased in AD cortical, but not hippocampal, samples. In contrast, MAO-B activity was increased in both regions (with a strong input from female donors) whether sample means were compared based on: (a) diagnosis alone; (b) diagnosis-by-APOE ε4 status (i.e., carriers vs. non-carriers of the ε4 allele); or (c) APOE ε4 status alone (i.e., ignoring 'diagnosis' as a variable). Sample means strictly based on the donor's sex did not reveal any difference in either MAO-A or MAO-B activity. Unexpectedly, we found that cortical MAO-A and MAO-B activities were highly correlated in both males and females (if focussing strictly on the donor's sex), while in the hippocampus, any correlation was lost in female samples. Stratifying for sex-by-APOE ε4 status revealed a strong correlation between cortical MAO-A and MAO-B activities in both non-carriers and carriers of the allele, but any correlation in hippocampal samples was lost in carriers of the allele. A diagnosis of AD disrupted the correlation between MAO-A and MAO-B activities in the hippocampus, but not the cortex. We observed a novel region-dependent co-regulation of MAO-A and MAO-B mRNAs (but not proteins), while a lack of correlation between MAO activities and the respective proteins corroborated previous reports. Overexpression of human APOE4 increased MAO activity (but not mRNA/protein) in C6 and in HT-22 cell cultures. We identified a novel co-regulation of MAO-A and MAO-B activities that is spared from any influence of risk factors for AD or AD itself in the cortex, but vulnerable to these same factors in the hippocampus. Sex- and region-dependent abilities to buffer influences on brain MAO activities could have significant bearing on ambiguous outcomes when monoaminergic systems are targeted in clinical populations.

Profiles of ß-Amyloid Peptides and Key Secretases in Brain Autopsy Samples Differ with Sex and APOE ε4 Status: Impact for Risk and Progression of Alzheimer Disease.

The APOE ε4 allele was originally reported to contribute to risk of Alzheimer's disease (AD) in women, yet male and female AD patient-derived data are routinely pooled. Histopathological hallmarks of AD include neurofibrillary tangles centered on hyperphosphorylated Tau and plaques composed of the ß-amyloid (Aß) peptide that is derived by sequential secretase-mediated cleavage of the Amyloid Protein Precursor (APP). We chose to examine profiles of Aß(1-40), Aß(1-42), and N-truncated (i.e., p3-related) fragments in the plaque-associated fraction of autopsied cortical and corresponding hippocampal samples from donors with a diagnosis of early-onset (EOAD) and late-onset (LOAD) AD. Levels of Aß(1-40), Aß(1-42), and the p3 fragment-enriched pool were increased in EOAD and LOAD samples, and correlated well within -but not between- regions. Counterintuitively, these increases were similar regardless of the AD donor's APOE ε4 status. Focusing on the donor's sex and APOE ε4 status as nominal variables (i.e., omitting diagnosis from the stratification) revealed that increases in Aß peptides were specific to female carriers of the ε4 allele and correlated with the proportional expression of BACE1/ß-secretase and ADAM10/α-secretase in the cortex and with nicastrin (γ-secretase) expression in the hippocampus. These data preliminarily support the possibility that AD follows distinct amyloidogenic processes in males and females, and that the APOE ε4 allele exerts a major influence on the disease process, particularly in women. This knowledge could significantly impact the (re)interpretation of unsuccessful outcomes of clinical interventions targeting either Aß peptides directly or the secretases implicated in APP processing.