Cannabinoid Receptor 2 Deficiency in Haematopoietic cells Aggravates Early Atherosclerosis in LDL Receptor Deficient Mice

Dissecting the role of cannabinoids in vascular health and disease

Cannabis, often recognized as the most widely used illegal psychoactive substance globally, has seen a shift in its legal status in several countries and regions for both recreational and medicinal uses. This change has brought to light new evidence linking cannabis consumption to various vascular conditions. Specifically, there is an association between cannabis use and atherosclerosis, along with conditions such as arteritis, reversible vasospasm, and incidents of aortic aneurysm or dissection. Recent research has started to reveal the mechanisms connecting cannabinoid compounds to atherosclerosis development. It is well known that the primary biological roles of cannabinoids operate through the activation of cannabinoid receptor types 1 and 2. Manipulation of the endocannabinoid system, either genetically or pharmacologically, is emerging as a promising approach to address metabolic dysfunctions related to obesity. Additionally, numerous studies have demonstrated the vasorelaxant properties and potential atheroprotective benefits of cannabinoids. In preclinical trials, cannabidiol is being explored as a treatment option for monocrotaline-induced pulmonary arterial hypertension. Although existing literature suggests a direct role of cannabinoids in the pathogenesis of atherosclerosis, the correlation between cannabinoids and other vascular diseases was only reported in some case series or observational studies, and its role and precise mechanisms remain unclear. Therefore, it is necessary to summarize and update previously published studies. This review article aims to summarize the latest clinical and experimental research findings on the relationship between cannabis use and vascular diseases. It also seeks to shed light on the potential mechanisms underlying these associations, offering a comprehensive view of current knowledge in this evolving field of study.

Role of the Endocannabinoidome in Human and Mouse Atherosclerosis

The Endocannabinoid (eCB) system and its role in many physiological and pathological conditions is well described and accepted, and includes cardiovascular disorders. However, the eCB system has been expanded to an "-ome"; the endocannabinoidome (eCBome) that includes endocannabinoid-related mediators, their protein targets and metabolic enzymes, many of which significantly impact upon cardiometabolic health. These recent discoveries are here summarized with a special focus on their potential involvement in atherosclerosis. We described the role of classical components of the eCB system (eCBs, CB1 and CB2 receptors) and eCB-related lipids, their regulatory enzymes and molecular targets in atherosclerosis. Furthermore, since increasing evidence points to significant cross-talk between the eCBome and the gut microbiome and the gut microbiome and atherosclerosis, we explore the possibility that a gut microbiome - eCBome axis has potential implications in atherosclerosis.

Role of autophagy in atherosclerosis: foe or friend?

Athrosclerosis is conceived as a chronic inflammatory status affecting cells from vascular walls. Different mechanisms and pathological features are evident at the onset of atherosclerotic changes via the engaging different cells from the vascular wall and circulatory cells. Attempts are currently focused on the detection of cell compensatory mechanisms against atherosclerotic changes to restore cell function and/or postpone severe vasculitis. Autophagy is an intracellular self-digesting process commonly protrudes exhausted organelles and injured cytoplasmic constituents via double-lipid bilayer membrane vesicles out the target cells. Recent investigations point to the critical and defensive role of autophagy in the vascular cells behavioral function such as endothelial cells and smooth muscle cells against different insults. Autophagy response and related effectors could be modulated in the favor to restore cell function and reduce pro-inflammatory status under pathological conditions. In this review, the recent findings were collected regarding the role of autophagy during atherosclerotic changes. We aimed to answer the question of how autophagy stimulation and/or inhibition could provide a promising effect on developing a sophisticated treatment for AS.

The Endocannabinoid System and Heart Disease: The Role of Cannabinoid Receptor Type 2

Decades of research has provided evidence for the role of the endocannabinoid system in human health and disease. This versatile system, consisting of two receptors (CB1 and CB2), their endogenous ligands (endocannabinoids), and metabolic enzymes has been implicated in a wide variety of disease states, ranging from neurological disorders to cancer. CB2 has gained much interest for its beneficial immunomodulatory role that can be obtained without eliciting psychotropic effects through CB1. Recent studies have shed light on a protective role of CB2 in cardiovascular disease, an ailment which currently takes more lives each year in Western countries than any other disease or injury. By use of CB2 knockout mice and CB2-selective ligands, knowledge of how CB2 signaling affects atherosclerosis and ischemia has been acquired, providing a major stepping stone between basic science and translational clinical research. Here, we summarize the current understanding of the endocannabinoid system in human pathologies and provide a review of the results from preclinical studies examining its function in cardiovascular disease, with a particular emphasis on possible CB2-targeted therapeutic interventions to alleviate atherosclerosis.

The CB2 receptor and its role as a regulator of inflammation

The CB2 receptor is the peripheral receptor for cannabinoids. It is mainly expressed in immune tissues, highlighting the possibility that the endocannabinoid system has an immunomodulatory role. In this respect, the CB2 receptor was shown to modulate immune cell functions, both in cellulo and in animal models of inflammatory diseases. In this regard, numerous studies have reported that mice lacking the CB2 receptor have an exacerbated inflammatory phenotype. This suggests that therapeutic strategies aiming at modulating CB2 signaling could be promising for the treatment of various inflammatory conditions. Herein, we review the pharmacology of the CB2 receptor, its expression pattern, and the signaling pathways induced by its activation. We next examine the regulation of immune cell functions by the CB2 receptor and the evidence obtained from primary human cells, immortalized cell lines, and animal models of inflammation. Finally, we discuss the possible therapies targeting the CB2 receptor and the questions that remain to be addressed to determine whether this receptor could be a potential target to treat inflammatory disease.

The roles of macrophage autophagy in atherosclerosis

Although various types of drugs and therapies are available to treat atherosclerosis, it remains a major cause of mortality throughout the world. Macrophages are the major source of foam cells, which are hallmarks of atherosclerotic lesions. Consequently, the roles of macrophages in the pathophysiology of atherosclerosis are increasingly investigated. Autophagy is a self-protecting cellular catabolic pathway. Since its discovery, autophagy has been found to be associated with a variety of diseases, including cardiovascular diseases, malignant tumors, neurodegenerative diseases, and immune system disorders. Accumulating evidence demonstrates that autophagy plays an important role in inhibiting inflammation and apoptosis, and in promoting efferocytosis and cholesterol efflux. These facts suggest the induction of autophagy may be exploited as a potential strategy for the treatment of atherosclerosis. In this review we mainly discuss the relationship between macrophage autophagy and atherosclerosis and the molecular mechanisms, as well as the recent advances in targeting the process of autophagy to treat atherosclerosis.

Monoglyceride lipase deficiency modulates endocannabinoid signaling and improves plaque stability in ApoE-knockout mice

Background and aims

Monoglyceride lipase (MGL) catalyzes the final step of lipolysis by degrading monoglyceride (MG) to glycerol and fatty acid. MGL also hydrolyzes and thereby deactivates 2-arachidonoyl glycerol (2-AG), the most abundant endocannabinoid in the mammalian system. 2-AG acts as full agonist on cannabinoid receptor type 1 (CB1R) and CB2R, which are mainly expressed in brain and immune cells, respectively. Thus, we speculated that in the absence of MGL, increased 2-AG concentrations mediate CB2R signaling in immune cells to modulate inflammatory responses, thereby affecting the development of atherosclerosis.

Methods and results

We generated apolipoprotein E (ApoE)/MGL double-knockout (DKO) mice and challenged them with Western-type diet for 9 weeks. Despite systemically increased 2-AG concentrations in DKO mice, CB2R-mediated signaling remains fully functional, arguing against CB2R desensitization. We found increased plaque formation in both en face aortae (1.3-fold, p = 0.028) and aortic valve sections (1.5-fold, p = 0.0010) in DKO mice. Interestingly, DKO mice also presented reduced lipid (12%, p = 0.031) and macrophage content (18%, p = 0.061), elevated intraplaque smooth muscle staining (1.4-fold, p = 0.016) and thicker fibrous caps (1.8-fold, p = 0.0032), together with a higher ratio of collagen to necrotic core area (2.5-fold, p = 0.0003) and expanded collagen content (1.6-fold, p = 0.0007), which suggest formation of less vulnerable atherosclerotic plaques. Treatment with a CB2R inverse agonist prevents these effects in DKO mice, demonstrating that the observed plaque phenotype in DKO mice originates from CB2R activation.

Conclusion

Loss of MGL modulates endocannabinoid signaling in CB2R-expressing cells, which concomitantly affects the pathogenesis of atherosclerosis. We conclude that despite larger lesion size loss of MGL improves atherosclerotic plaque stability. Thus, pharmacological MGL inhibition may be a novel intervention to reduce plaque rupture.

Cannabinoid Receptor Type 2 (CB2) Dependent and Independent Effects of WIN55,212-2 on Atherosclerosis in Ldlr-null Mice

PURPOSE

WIN55,212-2, a potent synthetic agonist of cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 (CB2), reduces atherosclerosis in apolipoprotein E (ApoE) null mice. Although pharmacologic evidence suggests the anti-atherosclerotic effects of WIN55,212-2 are mediated via CB2, this remains to be confirmed by genetic studies. Therefore, in this study, we investigated the effects of WIN55,212-2 on development of atherosclerosis in low-density lipoprotein receptor (Ldlr) null mice with and without homozygous deletion of the CB2 gene.

METHODS

After 6 weeks on an atherogenic diet, groups of CB2^+/+ and CB2^-/- Ldlr-null mice received a daily intraperitoneal injection of WIN55,212-2 or vehicle. After two weeks, plasma lipid levels and atherosclerosis in the aortic root were quantified.

RESULTS

Plasma cholesterol and triglyceride levels did not differ between CB2^+/+ and CB2^-/- mice and WIN55,212-2 had no effect on total cholesterol levels in either genotype. However, triglyceride levels in both CB2^+/+ and CB2^-/- mice were significantly lowered by WIN55,212-2. The size of aortic root lesions did not differ significantly between CB2^+/+ and CB2^-/- mice with or without WIN55,212-2 treatment. However, WIN55,212-2 treatment significantly lowered lesional macrophage accumulation in CB2^+/+ mice, and lesional smooth muscle content in both CB2^+/+ and CB2^-/- mice. Lesional apoptosis was also greater in CB2^+/+ mice compared to CB2^-/-mice, and only reduced by WIN55,212-2 in CB2^+/+ mice. Collagen content and elastin fiber fragmentation were unaffected by genotype or WIN55,212-2.

CONCLUSIONS

WIN55,212-2 treatment does not alter lesion size in Ldlr null-mice, but does modify lesion cellularity via CB2-dependent and CB2-independent mechanisms.

Activation of GPR55 Receptors Exacerbates oxLDL-Induced Lipid Accumulation and Inflammatory Responses, while Reducing Cholesterol Efflux from Human Macrophages

The G protein-coupled receptor GPR55 has been proposed as a new cannabinoid receptor associated with bone remodelling, nervous system excitability, vascular homeostasis as well as in several pathophysiological conditions including obesity and cancer. However, its physiological role and underlying mechanism remain unclear. In the present work, we demonstrate for the first time its presence in human macrophages and its increased expression in ox-LDL-induced foam cells. In addition, pharmacological activation of GPR55 by its selective agonist O-1602 increased CD36- and SRB-I-mediated lipid accumulation and blocked cholesterol efflux by downregulating ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, as well as enhanced cytokine- and pro-metalloprotease-9 (pro-MMP-9)-induced proinflammatory responses in foam cells. Treatment with cannabidiol, a selective antagonist of GPR55, counteracted these pro-atherogenic and proinflammatory O-1602-mediated effects. Our data suggest that GPR55 could play deleterious role in ox-LDL-induced foam cells and could be a novel pharmacological target to manage atherosclerosis and other related cardiovascular diseases.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Targeting cannabinoid receptor CB(2) in cardiovascular disorders: promises and controversies

Cardiovascular disease is the leading cause of death and disability worldwide, which can be largely attributed to atherosclerosis, a chronic inflammation of the arteries characterized by lesions containing immune and smooth muscle cells, lipids and extracellular matrix. In recent years, the lipid endocannabinoid system has emerged as a new therapeutic target in variety of disorders associated with inflammation and tissue injury, including those of the cardiovascular system. The discovery that Δ-9-tetrahydrocannabinol (Δ9-THC), the main active constituent of marijuana, inhibited atherosclerotic plaque progression via a cannabinoid 2 (CB(2) ) receptor-dependent anti-inflammatory mechanism, and that certain natural and synthetic cannabinoid ligands could modulate the myocardial or cerebral ischaemia-reperfusion-induced tissue damage, have stimulated impetus for a growing number of studies investigating the implication of CB(2) receptors in atherosclerosis, restenosis, stroke, myocardial infarction and heart failure. The aim of this review is to update on recent findings and controversies on the role of CB(2) receptors in cardiovascular disease. Particular emphasis will be placed on novel insights in the potential cellular targets of CB(2) stimulation in cardiovascular system (e.g. endothelial and vascular smooth muscle cells, cardiomyocytes, infiltrating and/or resident monocytes/macrophages and leukocytes, etc.), their interplay and intracellular signalling mechanisms identified, as well as on experimental and clinical studies.

Bone marrow transplantation as an established approach for understanding the role of macrophages in atherosclerosis and the metabolic syndrome

PURPOSE OF REVIEW

Bone marrow transplantation (BMT) technology is a firmly established tool for studying atherosclerosis. Only recently it is helping us to understand the inflammatory mechanisms leading to the development of obesity, insulin resistance and type 2 diabetes. Here we review the use of BMT as a tool for studying the metabolic syndrome.

RECENT FINDINGS

Bone marrow-derived cells, and particularly monocytes and macrophages, have been a major subject in the study of atherogenesis, and they are highly amenable for research purposes because of their application in bone marrow transplantations. For example, the many pathways studied using BMT have helped unmask ABC transporters as the genes controlling reverse cholesterol transport and foam cell formation, as well as other genes like CCR2 and IκBα controlling leukocyte development, migration and activation. The invasion of leukocytes, not only in the vessel wall, but also in adipose tissue and liver, shares many common mechanisms relevant to atherosclerosis and metabolic diseases.

SUMMARY

BMT is an efficient and versatile tool for assessing the roles of specific genes that are restricted to hematopoietic cells, and especially the monocytes and macrophages in metabolic syndrome and its related pathologies.