Pascal Bernatchez

Associate Professor

Research Interests

Cardiovascular diseases
Cardiovascular System
Genetic Diseases
Hypertension
atherosclerosis
angiogenesis
Muscular Diseases
Neuromuscular Diseases
Lipid/Lipoprotein analysis
Lipid Disorders
Pharmacokinetics
Cell Signaling and Infectious and Immune Diseases
angiogenesis
atherosclerosis
endothelial dysfunction
endothelium
Inflammation
lipoproteins
Marfan syndrome
muscular dystrophy
nitric oxide
vascular disease

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transgenic
cell culture
Histology
Western blot
PCR
plasma

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Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

The role of endothelial function in Marfan syndrome associated aortic root aneurysm: time to look beyond blood pressure control (2022)

Marfan syndrome (MFS), a connective tissue disorder caused by mutations in the fibrillin-1 gene (FBN1), leads to progressive aortic root aneurysm. With no cure, MFS management relies on life-long use of blood pressure (BP)-lowering medications, mainly β-blockers or the angiotensin II (AngII) receptor type 1 (AT1R) blocker (ARB) losartan in an attempt to reduce aortic dilation rates and delay replacement surgery. However, despite many large-scale studies, conflicting clinical data have highlighted the underwhelming efficacy of BP-lowering-based pharmacotherapy at preventing aortic root widening, casting doubt on the therapeutic value of BP-lowering in MFS. In contrast, emerging evidence suggest the vascular endothelium and the nitric oxide (NO) system play a role in MFS aortic pathology and thus provide a novel therapeutic target for improving MFS management. Herein, using a mouse model of MFS, we demonstrate that BP-lowering with ARBs is of low therapeutic benefit to aortic root stability. The ARBs valsartan and losartan are both effective at attenuating aortic root widening and enhancing endothelial function despite valsartan being administered at a non-BP-lowering dose compared to losartan. Furthermore, telmisartan, an ARB most capable of enhancing endothelial function, can fully prevent MFS aortic root aneurysm through an endothelial NO synthase (eNOS)-dependent pathway, as in vivo inhibition of NOS activation renders telmisartan ineffective. Additionally, RNAseq data reveals smooth muscle cell genes potentially involved in the eNOS-dependent regulation of telmisartan’s effects on aortic remodeling. Lastly, we highlight ARB heterogeneity at activating endothelial function when administered at equivalent low BP-lowering doses. We show telmisartan to be the most potent activator of endothelial function among all clinically available ARBs and show this low-dose capable at attenuating MFs aortic root pathology further supporting endothelial function as the therapeutic driver behind ARBs’ anti-aortic remodeling effects.Overall, these studies establish the concept of achieving aortic root stability with ARBs in absence of BP-lowering and further identify eNOS-dependent activation of vascular endothelial function as a therapeutic driver of ARBs in MFS management. Moreover, these studies may aid in future MFS management guidelines with less focus on BP-lowering and more on endothelial function enhancement as well as guide future therapeutic development.

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Vascular biology of marfan syndrome: angiotensin II receptors, losartan, and nitric oxide (2017)

Marfan syndrome (MFS), a connective tissue disorder triggered by mutations in Fibrillin-1, causes life-threatening pathology including aortic aneurysm. Recently, controversy has arisen regarding the use of anti-hypertensive angiotensin-II (AngII) receptor type 1 (ATR1) blocker losartan in MFS as, despite success in animal models, losartan has failed to show superiority over standard β-adrenergic receptor blocker atenolol in preventing or slowing expansion of aortic root aneurysm in MFS patients. Overall, we hypothesized that we could provide new insight into this controversy via development of a novel MFS murine model lacking functional ATR1 signaling. Herein, using this novel model, we demonstrate that MFS aortic, pulmonary and skeletal pathology as well as the therapeutic benefit of losartan in MFS aneurysm prevention are ATR1-independent. Instead, we reveal the primary therapeutic pathway of losartan in MFS to be nitric oxide synthase (NOS)-dependent, as treatment of MFS aneurysm in vivo has no benefit upon inhibition of NOS. Furthermore, losartan is shown to mediate increased NO release in endothelial cells in the absence of AngII and correct NO levels in the plasma of MFS mice. In addition, declining plasma nitric oxide (NO) levels in mice were found to correlate to increasing aortic aneurysm size and sub-analysis of patients treated with losartan shows indices of improved endothelial function to correlate to regression of aortic aneurysm. Finally, we demonstrate the clinical potential of targeting endothelial dysfunction in MFS as murine models of endothelial nitric oxide synthase (eNOS) over-expression and hyper-activation as well as pharmacological activation of endogenous eNOS all result in prevention of MFS aneurysm. Overall, this study is the first to identify key aspects of MFS pathology and treatment including the ATR1-independent nature of MFS aortic, lung, and skeletal pathology and therapeutic benefit of losartan. Moreover, these studies are the first to show a NOS-dependent mechanism of losartan and therapeutic benefit of increasing NO bioavailability and improving endothelial function in MFS. As such, they collectively provide a basis for guiding the evolution of managing and treating MFS as well as future pharmaceutical development.

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Identifying and Characterizing Caveolin-1 Derived Peptides: A Novel Approach to Promoting Nitric Oxide Release from the Endothelium (2016)

Cardiovascular diseases are one of the largest causes of mortality globally. One of the hallmarks of cardiovascular diseases is a reduction in systemic endothelial nitric oxide synthase (eNOS)-derived Nitric Oxide (NO), a critical regulator of vascular homeostasis. eNOS regulation is complex, involving phosphorylation and direct protein interactions. The main negative regulator is caveolin-1 (Cav-1), the homo-oligomeric coat protein of caveolae, which interacts with eNOS via its scaffolding domain (CAV). Studies have shown that alanine substitution of F92 in CAV can lead to abolishment of the inhibitory effect on eNOS; furthermore, CAV peptides with the F92A substitution can be used as an antagonist to promote basal eNOS-derived NO to reduce blood pressure and reduce cardiovascular disease progression. We hypothesized that identification of the eNOS binding motif in CAV could be used as the basis for a pharmacophore to develop antagonists aimed at increasing vascular NO. We performed a protein interaction study to identify a 10 residue ‘binding site peptide’ (BSP) in CAV that could account for the majority of eNOS binding. Both BSP and its F92A counterpart (BSPF92A) bound eNOS with similar affinity as the full CAV sequence as confirmed by polarization assay, while computational modeling suggested that the peptides inserted themselves in to a hydrophobic pocket in eNOS.While substitution of F92 prevents inhibition of activated eNOS, we found that both BSP and BSPF92A could promote basal NO release from resting endothelial cells (ECs), independent of cell permeabilization sequence used. Furthermore, BSP and BSPF92A generated NO in an eNOS and lipid raft dependent manner. Subsequently, we found that neither BSP nor BSPF92A affected basic biochemical properties of eNOS and Cav-1, such as oligomerization, subcellular targeting and co-localization. Instead, the presence of F92 was found to promote phosphorylation of eNOS, an important step in its activation. As a result of this finding, we have identified the basis for two different pharmacophores that increase NO in different manners. One that promotes activity indirectly (BSP) while the other one acts as an antagonist (BSPF92A). We hope to use this as the beginnings for a therapeutics development platform to promote cardioprotective NO.

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The Role of Myoferlin and Dysferlin in Lung Epithelial Cell Membrane Functions and Lung Cancer (2015)

No abstract available.

Therapeutic use of a Mutant Caveolin-1 Peptide to Reduce Atherosclerosis Induced by Hypercholesterolemia and Diabetes (2015)

No abstract available.

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Characterizing the effect of caveolin-1 mutations and age-related changes in the caveolin-1 signalling interaction with endothelial nitric oxide synthase (2023)

Caveolin-1 (Cav1) is a membrane protein that plays important structural and signalling roles in several mammalian cell types. While best known for the formation of flask-shaped membrane structures known as caveolae, which have been implicated in endocytic, mechanoprotective, and signalling roles, Cav1 also readily oligomerizes within lipid rafts to form Cav1 domains known as scaffolds. Disrupting Cav1 expression promotes tumour survival and migration, and Cav1 knockout animals suffer from pulmonary and cardiovascular conditions. While Cav1 is well-known to interact with multiple cell signalling partners, notably its inhibition of endothelial nitric oxide synthase (eNOS), it remains unclear if this interaction is caveolae- or scaffold-dependent, of if it involves the caveolin scaffolding domain or the tyrosine-14 residue of Cav1.Here, we used confocal and single molecule localization microscopy (SMLM) network analysis of Cav1 and eNOS localization in a transiently transfected Cav1 knockout MDA-MB-231 cell line, as well as whole-mount labeling of Cav1 and eNOS in mouse pulmonary arteries to study Cav1 interaction with eNOS. We found that phosphomimetic Cav1-Y14D mutant caveolae and scaffolds had similar features to caveolin scaffolding domain (CSD) mutants, while phosphorylation-deficient Cav1-Y14F mutant Cav1 structures closely resembled Cav1-WT blobs. Using binary mask analyses of Cav1 and eNOS, we identified that eNOS interacts with caveolae and scaffolds approximately equally, and that CSD mutant and Y14D mutant Cav1 had a slight but non-significant increase in Cav1-eNOS co-occurrence across all Cav1 domains.Additionally, to investigate changes in Cav1 and eNOS localization and behaviour with age, we used confocal microscopy to image Cav1, eNOS, and the Golgi marker GM130 in the pulmonary artery endothelium young and old mice. We observed that eNOS expression decreases with age (p
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Effects of thermoneutrality on dysferlin-deficient muscular dystrophy (2021)

Limb-Girdle Muscular Dystrophy (MD) Type 2B (LGMD2B) is a rare form of MD caused by mutations in the dysferlin (DYSF) gene. As an autosomal recessive disorder, LGMD2B can occur in both males and females and is characterized by progressive muscle wasting, eventually leading to ambulatory dysfunction. Unfortunately, no treatment options can cure patients of LGMD2B. One potential factor in the lack of therapies is the absence of humanized animal models for preclinical studies. Current LGMD2B mouse models lack the disease severity typically observed in the human condition. Additionally, LGMD2B mice remain mobile, whereas most patients are non-ambulatory or exhibit a marked decrease in mobility. Developing more humanized animal models of LGMD2B is vital for improvements in LGMD2B research. Recently, our lab has shown that crossing a DYSF knockout mouse with a mouse lacking apolipoprotein E (ApoE), a surface transport lipoprotein, significantly raises plasma cholesterol and correlates with a severe muscle wasting phenotype and marked ambulatory dysfunction. However, LGMD2B patients have an intact ApoE gene, demonstrating a major limitation of this model. Regardless, the DYSF/ApoE double knockout (DKO) mouse provides proof of principle that dyslipidemia plays a factor in LGMD2B pathology and warrants further investigations. Since thermoneutral (TN) housing of wild type mice has been shown to increase plasma lipids significantly when fed a western diet (WD), we hypothesized that TN housing of BLAJ mice, a mild model of LGMD2B, would lead to an exacerbation of muscle wasting when fed a cholesterol-rich WD. Herein, we report that TN BLAJ mice fed a cholesterol-rich WD exhibited the greatest level of fibrofatty replacement, despite not increasing plasma cholesterol. Additionally, thermoneutrality affected LGMD2B mice in a sex-specific manner, with females having significantly more fibrofatty replacement than males. Finally, TN BLAJ mice fed a cholesterol-rich WD had increases in mTORC1 regulated protein synthesis, in addition to a decrease in LC3 mediated autophagy, suggesting an overall decrease in protein turnover within DYSF-null skeletal muscle. In conclusion, this study reveals BLAJ mice to be sensitive to changes in ambient temperature and suggests that alterations in metabolism could be a contributing factor in LGMD2B pathology.

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Effects of hyperlipidemia on dysferlin- and dystrophin-deficient muscular dystrophies in double-disease mouse models (2017)

Muscular dystrophy (MD) is a class of diseases marked by progressive muscle wasting and impaired ambulatory function. Dysferlin- and dystrophin-deficiencies lead to MD and both are expressed in myofibers as well as smooth muscle and endothelial cells lining the vasculature, suggesting vascular function may be a contributing factor to muscle pathology seen in MD. However, murine models of MD develop only mild pathology compared to patients, making therapeutic drug development challenging. Since mice are known to have endogenously low lipid levels and superior vascular health, disrupted vascular function may be aggravating MD progression in humans. We seek to investigate the effect of impaired vascular function on MD pathology through the generation and characterization of doubledisease murine models affected by both hyperlipidemia and MD. Firstly, the dysferlin-null (Dysf-KO) model of limb-girdle type 2B MD (LGMD2B) and the dystrophin-null (mdx) model of Duchenne MD (DMD) were crossed with apolipoprotein E-KO (ApoE-KO) hyperlipidemia model to generate Dysf-ApoE and Mdx-ApoE double-knockout mice (DKO). To further confirm the effects vascular disease on MD using a more human-relevant model, the Dysf-KO model was also crossed with the milder low-density-lipoprotein receptor-knockout (LDLRKO) model of hyperlipidemia. Significant worsening of ambulatory function and muscle pathology was observed in the Dysf-ApoE DKO model, displaying reduced stride length, sometimes complete loss of ambulation, and increased muscle wasting, necrosis, fibrosis and fat infiltration. Although the Mdx-ApoE model showed no exacerbation of ambulation decline, significant worsening of muscle necrosis and fibrofatty replacement was observed in MdxApoE DKO mice. However, few Dysf-LDLR DKOs were produced; all were maloccluded runts with abnormal gait, though without observable muscle pathology upon histological analysis. In all, the Dysf-ApoE and Mdx-ApoE mice demonstrate that hyperlipidemia and associated vascular disease can dramatically aggravate muscle pathology in MD. These double-disease models mimic more closely the severity of human MD and may be useful for evaluating therapeutic interventions. In addition, these data suggest that lipid-lowering and vascular-targeted therapies may be beneficial in LGMD2B and DMD.

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Molecular and pharmacological characterization of mutant (F92A) caveolin-1: a direction towards increasing nitric oxide bioavailability (2010)

Nitric Oxide (NO) produced by the endothelium is a critical mediator of vascular function and plays an important role in the protection against various cardiovascular diseases1. In fact, a central feature of most cardiovascular diseases is reduced bioavailability of NO resulting from impaired endothelial function. Consequently, therapies that improve NO synthesis and availability in disease settings are relevant. Endothelial nitric oxide synthase (eNOS) is a membrane enzyme expressed exclusively in vascular endothelial cells and is responsible for NO production. Improper regulation of the enzyme results in production of eNOS-derived superoxide anion (O₂₋) instead of NO. O₂₋ is an oxidative stress mediator and scavenges NO, thereby contributing to lowered NO bioavailability. Extensive research has demonstrated a number of factors involved in positively regulating eNOS activity. However, one of the few proteins that bind to eNOS under basal conditions and inhibit NO release is Caveolin-1 (Cav-1), the major coat protein of plasma membrane lipid-enriched invaginations known as caveolae². Recently, it was demonstrated that a single amino acid substitution of the Cav-1 protein, mutant known as F92A Cav-1, is unable to inhibit eNOS³. Furthermore, preliminary data indicates that high expression of F92A Cav-1 can increase basal NO release. Due to the significance of NO in vascular function, the current work explores the possible mechanisms by which F92A Cav-1 potentiates eNOS activity and NO release. We report that F92A Cav-1 preserves the unique properties of Cav-1, including targeting to caveolae and forming high molecular weight oligomers, which are essential for caveolae organelle biogenesis. Moreover, F92A Cav-1 still retains the ability to bind to eNOS without altering its subcellular localization, indicating that F92A Cav-1 can prevent eNOS binding to endogenous Cav-1, which could rationalize the increased NO release observed. Lastly, we provide evidence that over-expression of F92A Cav-1 reduces the release of basal O₂₋ in endothelial cells as compared to WT Cav-1, revealing another potential positive effect of the mutant Cav-1. Hence, this report compares the biological properties of WT and F92A Cav-1 and the data collected is aimed at describing a therapeutically relevant pharmacological target to increase NO bioavailability in cardiovascular disease settings.

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Myoferlin-dependent regulation of receptor tie-2: characterization of a novel endothelial-specific anti-angiogenesis target (2010)

Heart disease and cancer are the two leading causes of death worldwide. In heart disease, reperfusion of an ischemic myocardium through increased angiogenesis, or the growth of new blood vessels, is considered the ‘holy grail’ of future therapies. In contrast, inhibiting tumour growth by decreasing angiogenesis through anti-angiogenic therapies is increasingly used in cancer patients, although the therapeutic effect is only partial. Hence, a better comprehension of angiogenesis is clearly warranted. While a plethora of literature suggests that the vascular endothelial growth factor (VEGF) and angiopoietins systems are the most potent endogenous regulators of angiogenesis, an increasing number of recent studies also show that their net angiogenic effects are mostly dictated by membrane expression of their main receptors, VEGFR-2 and tie-2, respectively. Recently, endothelial cells (ECs) were unexpectedly found to express myoferlin, a muscle protein [1] known for its ability to regulate plasma membrane integrity [2]. Moreover, myoferlin was found to be involved in the regulation of VEGFR-2 expression in ECs [3]. In this work, we report that disruption of myoferlin by gene-silencing causes decreased tie-2 expression in cultured ECs. However, myoferlin disruption does not affect the transcriptional levels of tie-2 in cultured ECs. Separation of caveolae/lipid rafts from cytosol in ECs shows presence of myoferlin and tie-2 in caveolae/lipid rafts, suggesting co-localization of the two proteins to form a large signaling complex at caveoli, which are known platforms for clustering of signaling complexes. Moreover, myoferlin is present in a cancer cell model (Lewis Lung Carcinoma) and myoferlin disruption causes decreased cell proliferation, further exploring the involvement of this membrane protein in a completely different cell system. The current work identifies potential pharmacological targets for the regulation of the tie-2 system and since tie-2 expression is almost exclusively found in ECs, this work initiates the characterization of an EC-specific target that could be further exploited to modulate angiogenic responses in an in vivo model.

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