Pharmacological Blockade of Cannabinoid CB1 Receptors in Diet-Induced Obesity Regulates Mitochondrial Dihydrolipoamide Dehydrogenase in Muscle

The Role of Cannabinoid-1 Receptor Ligands in the Ovalbumin-Induced Mouse Model of Allergic Asthma: Is It Related to Transient Receptor Potential Vanilloid-1 Channels?

Objectives: The aim of this study was to investigate the role of cannabinoid (CB1) receptors on airway inflammation and hypersensitivity in allergic asthma and the potential interactions with TRPV1 channels. Materials and Methods: BALB/c mice were sensitized and provoked with ovalbumin to create a model of allergic asthma. CB1 selective agonist arachidonoyl 2'-chloroethylamide (ACEA) was administered intraperitoneally at doses of 0.5, 3, and 5 mg/kg. Receptor antagonism studies were performed utilizing selective CB1 antagonists AM251 at a dose of 3 mg/kg. TRPV1 channel was selectively blocked by capsazepine at a dose of 2.5 mg/kg. Penh values were recorded in vivo by a whole-body plethysmograph under methacholine challenge. Inflammatory cell count was performed in bronchoalveolar lavage fluid (BALF). Serum levels of proinflammatory cytokines were measured by Enzyme-Linked ImmunoSorbent Assay (ELISA). Inflammation in the lung tissue was scored histopathologically. Statistical significance was determined using one-way analysis of variance or Kruskal-Wallis test and expressed as p<0.05. Results: In sensitized animals, provocation with inhaled ovalbumin increased Penh values, serum interleukin (IL)-4, IL-5, IL-13 levels, eosinophil, neutrophil, lymphocyte, macrophage counts in BALF, and inflammation in the lung tissue. ACEA applications did not significantly alter Penh values, BALF inflammatory cell levels, and histological changes related to inflammation in the lung tissue according to the disease group; however, only at a dose of 5 mg/kg, it reduced the levels of the inflammatory cytokine IL-4. AM251 decreased Penh values, eosinophil and neutrophil migration in BALF, and inflammation score of lung tissue compared with the disease group. Although BALF inflammatory cell levels and Penh values were higher in the AM251+ACEA group than in the AM251 group, the differences were insignificant. In the CPZ+ACEA group, Penh values were significantly higher, and serum IL-4 and IL-13 levels and BALF eosinophil counts were lower than that in the CPZ group. Conclusions: This study demonstrated an important role of the CB1 receptors in allergic asthma. CB1 antagonism reduced airway hyperresponsiveness and inflammation and showed immunomodulatory effects. The effect of the CB1 agonist ACEA on asthma does not appear to be related to TRPV1 channels.

Effect of CB1 Receptor Deficiency on Mitochondrial Quality Control Pathways in Gastrocnemius Muscle

This study aims to explore the complex role of cannabinoid type 1 receptor (CB1) signaling in the gastrocnemius muscle, assessing physiological processes in both CB1+/+ and CB1-/- mice. The primary focus is to enhance our understanding of how CB1 contributes to mitochondrial homeostasis. At the tissue level, CB1-/- mice exhibit a substantial miRNA-related alteration in muscle fiber composition, characterized by an enrichment of oxidative fibers. CB1 absence induces a significant increase in the oxidative capacity of muscle, supported by elevated in-gel activity of Complex I and Complex IV of the mitochondrial respiratory chain. The increased oxidative capacity is associated with elevated oxidative stress and impaired antioxidant defense systems. Analysis of mitochondrial biogenesis markers indicates an enhanced capacity for new mitochondria production in CB1-/- mice, possibly adapting to altered muscle fiber composition. Changes in mitochondrial dynamics, mitophagy response, and unfolded protein response (UPR) pathways reveal a dynamic interplay in response to CB1 absence. The interconnected mitochondrial network, influenced by increased fusion and mitochondrial UPR components, underlines the dual role of CB1 in regulating both protein quality control and the generation of new mitochondria. These findings deepen our comprehension of the CB1 impact on muscle physiology, oxidative stress, and MQC processes, highlighting cellular adaptability to CB1-/-. This study paves the way for further exploration of intricate signaling cascades and cross-talk between cellular compartments in the context of CB1 and mitochondrial homeostasis.

Exerkines, Nutrition, and Systemic Metabolism

The cornerstones of good health are exercise, proper food, and sound nutrition. Physical exercise should be a lifelong routine, supported by proper food selections to satisfy nutrient requirements based on energy needs, energy management, and variety to achieve optimal metabolism and physiology. The human body is sustained by intermediary and systemic metabolism integrating the physiologic processes for cells, tissues, organs, and systems. Recently, interest in specific metabolites, growth factors, cytokines, and hormones called exerkines has emerged to explain cooperation between nutrient supply organs and the brain during exercise. Exerkines consist of different compounds described as signaling moiety released during and after exercise. Examples of exerkines include oxylipin 12, 13 diHOME, lipid hormone adiponectin, growth factor BDNF, metabolite lactate, reactive oxygen species (ROS), including products of fatty acid oxidation, and cytokines such as interleukin-6. At this point, it is believed that exerkines are immediate, fast, and long-lasting factors resulting from exercise to support body energy needs with an emphasis on the brain. Although exerkines that are directly a product of macronutrient metabolism such as lactate, and result from catabolism is not surprising. Furthermore, other metabolites of macronutrient metabolism seem to be candidate exerkines. The exerkines originate from muscle, adipose, and liver and support brain metabolism, energy, and physiology. The purpose of this review is to integrate the actions of exerkines with respect to metabolism that occurs during exercise and propose other participating factors of exercise and brain physiology. The role of diet and macronutrients that influence metabolism and, consequently, the impact of exercise will be discussed. This review will also describe the evidence for PUFA, their metabolic and physiologic derivatives endocannabinoids, and oxylipins that validate them being exerkines. The intent is to present additional insights to better understand exerkines with respect to systemic metabolism.

Identification of biomarkers, pathways, and potential therapeutic targets for heart failure using next-generation sequencing data and bioinformatics analysis

BACKGROUND

Heart failure (HF) is the most common cardiovascular diseases and the leading cause of cardiovascular diseases related deaths. Increasing molecular targets have been discovered for HF prognosis and therapy. However, there is still an urgent need to identify novel biomarkers. Therefore, we evaluated biomarkers that might aid the diagnosis and treatment of HF.

METHODS

We searched next-generation sequencing (NGS) dataset (GSE161472) and identified differentially expressed genes (DEGs) by comparing 47 HF samples and 37 normal control samples using limma in R package. Gene ontology (GO) and pathway enrichment analyses of the DEGs were performed using the g: Profiler database. The protein-protein interaction (PPI) network was plotted with Human Integrated Protein-Protein Interaction rEference (HiPPIE) and visualized using Cytoscape. Module analysis of the PPI network was done using PEWCC1. Then, miRNA-hub gene regulatory network and TF-hub gene regulatory network were constructed by Cytoscape software. Finally, we performed receiver operating characteristic (ROC) curve analysis to predict the diagnostic effectiveness of the hub genes.

RESULTS

A total of 930 DEGs, 464 upregulated genes and 466 downregulated genes, were identified in HF. GO and REACTOME pathway enrichment results showed that DEGs mainly enriched in localization, small molecule metabolic process, SARS-CoV infections, and the citric acid tricarboxylic acid (TCA) cycle and respiratory electron transport. After combining the results of the PPI network miRNA-hub gene regulatory network and TF-hub gene regulatory network, 10 hub genes were selected, including heat shock protein 90 alpha family class A member 1 (HSP90AA1), arrestin beta 2 (ARRB2), myosin heavy chain 9 (MYH9), heat shock protein 90 alpha family class B member 1 (HSP90AB1), filamin A (FLNA), epidermal growth factor receptor (EGFR), phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), cullin 4A (CUL4A), YEATS domain containing 4 (YEATS4), and lysine acetyltransferase 2B (KAT2B).

CONCLUSIONS

This discovery-driven study might be useful to provide a novel insight into the diagnosis and treatment of HF. However, more experiments are needed in the future to investigate the functional roles of these genes in HF.

Genetic Manipulation of CB1 Cannabinoid Receptors Reveals a Role in Maintaining Proper Skeletal Muscle Morphology and Function in Mice

The endocannabinoid system (ECS) refers to a widespread signaling system and its alteration is implicated in a growing number of human diseases. Cannabinoid receptors (CBRs) are highly expressed in the central nervous system and many peripheral tissues. Evidence suggests that CB1Rs are expressed in human and murine skeletal muscle mainly in the cell membrane, but a subpopulation is present also in the mitochondria. However, very little is known about the latter population. To date, the connection between the function of CB1Rs and the regulation of intracellular Ca²⁺ signaling has not been investigated yet. Tamoxifen-inducible skeletal muscle-specific conditional CB1 knock-down (skmCB1-KD, hereafter referred to as Cre^+/-) mice were used in this study for functional and morphological analysis. After confirming CB1R down-regulation on the mRNA and protein level, we performed in vitro muscle force measurements and found that peak twitch, tetanus, and fatigue were decreased significantly in Cre^+/- mice. Resting intracellular calcium concentration, voltage dependence of the calcium transients as well as the activity dependent mitochondrial calcium uptake were essentially unaltered by Cnr1 gene manipulation. Nevertheless, we found striking differences in the ultrastructural architecture of the mitochondrial network of muscle tissue from the Cre^+/- mice. Our results suggest a role of CB1Rs in maintaining physiological muscle function and morphology. Targeting ECS could be a potential tool in certain diseases, including muscular dystrophies where increased endocannabinoid levels have already been described.

Molecular networks underlying cannabinoid signaling in skeletal muscle plasticity

The cannabinoid system is ubiquitously present and is classically considered to engage in neural and immunity processes. Yet, the role of the cannabinoid system in the whole body and tissue metabolism via central and peripheral mechanisms is increasingly recognized. The present review provides insights in (i) how cannabinoid signaling is regulated via receptor-independent and -dependent mechanisms and (ii) how these signaling cascades (might) affect skeletal muscle plasticity and physiology. Receptor-independent mechanisms include endocannabinoid metabolism to eicosanoids and the regulation of ion channels. Alternatively, endocannabinoids can act as ligands for different classic (cannabinoid receptor 1 [CB₁ ], CB₂ ) and/or alternative (e.g., TRPV1, GPR55) cannabinoid receptors with a unique affinity, specificity, and intracellular signaling cascade (often tissue-specific). Antagonism of CB₁ might hold clues to improve oxidative (mitochondrial) metabolism, insulin sensitivity, satellite cell growth, and muscle anabolism, whereas CB₂ agonism might be a promising way to stimulate muscle metabolism and muscle cell growth. Besides, CB₂ ameliorates muscle regeneration via macrophage polarization toward an anti-inflammatory phenotype, induction of MyoD and myogenin expression and antifibrotic mechanisms. Also TRPV1 and GPR55 contribute to the regulation of muscle growth and metabolism. Future studies should reveal how the cannabinoid system can be targeted to improve muscle quantity and/or quality in conditions such as ageing, disease, disuse, and metabolic dysregulation, taking into account challenges that are inherent to modulation of the cannabinoid system, such as central and peripheral side effects.

Mitochondrial Localization of CB1 in Progesterone-producing Cells of Ovarian Interstitial Glands of Adult Mice

Localization of cannabinoid receptor type 1 (CB1) immunoreactivity on mitochondrial membranes, at least their outer membranes distinctly, was detected in progesterone-producing cells characterized by mitochondria having tubular cristae and aggregations of lipid droplets in ovarian interstitial glands in situ of adult mice. Both immunoreactive and immunonegative mitochondria were contained in one and the same cell. Considering that the synthesis of progesterone is processed in mitochondria, the mitochondrial localization of CB1 in the interstitial gland cells suggests the possibility that endocannabinoids modulate the synthetic process of progesterone in the cells through CB1.

Cannabidiol Does Not Impact Acute Anabolic or Inflammatory Signaling in Skeletal Muscle In Vitro

Background: Cannabidiol (CBD) is becoming increasingly popular for the treatment of clinical conditions including as an aid for muscle recovery. Previous work demonstrated that CBD exhibited mild effects on skeletal muscle, with a tendency to increase anabolic signaling and decrease inflammatory signaling. Methods: To gain mechanistic insight and extend these findings, we conducted a set of experiments using C2C12 myotubes. Results: Increasing the dose of CBD (1-5 μM) provided with insulin-like growth factor 1 (IGF-1) showed no effect on anabolic signaling through mTORC1 (S6K1 [Thr389], p=0.27; rpS6 [Ser240/244], p=0.81; or 4E-BP1 [Thr37/46], p=0.87). Similarly, inflammatory signaling through nuclear factor kappa B (NF-κB) (p105, p=0.88; p50, p=0.93; or phosphorylated p65 [Ser536], p=0.84) in response to tumor necrosis factor α (TNFα) was unaffected by CBD (2.5 μM), whereas dioscin, a natural product that blocks NF-κB signaling, reduced p105 and phosphorylated p65 (Ser536) compared with the TNFα and the TNFα + CBD condition (p<0.01 and p<0.05, respectively). Finally, cannabinoid receptor type 1 (CB1) receptor levels were measured in C2C12 cells, murine skeletal muscle, cortex, and hippocampus. Although CB1 was not detectable in muscle cells or muscle tissue, high levels were observed in brain tissue. Conclusion: In conclusion, CBD does not directly modulate anabolic or inflammatory signaling in myotubes in vitro, which can likely be explained by the lack of functional receptors.

Assessing the Potential of Nutraceuticals as Geroprotectors on Muscle Performance and Cognition in Aging Mice

Aging and frailty are associated with a decline in muscle force generation, which is a direct consequence of reduced muscle quantity and quality. Among the leading contributors to aging is the generation of reactive oxygen species, the byproducts of terminal oxidation. Their negative effects can be moderated via antioxidant supplementation. Krill oil and astaxanthin (AX) are nutraceuticals with a variety of health promoting, geroprotective, anti-inflammatory, anti-diabetic and anti-fatigue effects. In this work, we examined the functional effects of these two nutraceutical agents supplemented via pelleted chow in aging mice by examining in vivo and in vitro skeletal muscle function, along with aspects of intracellular and mitochondrial calcium homeostasis, as well as cognition and spatial memory. AX diet regimen limited weight gain compared to the control group; however, this phenomenon was not accompanied by muscle tissue mass decline. On the other hand, both AX and krill oil supplementation increased force production without altering calcium homeostasis during excitation-contraction coupling mechanism or mitochondrial calcium uptake processes. We also provide evidence of improved spatial memory and learning ability in aging mice because of krill oil supplementation. Taken together, our data favors the application of antioxidant nutraceuticals as geroprotectors to improve cognition and healthy aging by virtue of improved skeletal muscle force production.

The effects of systemic and local fatty acid amide hydrolase and monoacylglycerol lipase inhibitor treatments on the metabolomic profile of lungs

The contribution of the endocannabinoid system to both physiology and pathological processes in the respiratory system makes it a promising target for inflammatory airway diseases. Previously, we have shown that increasing the tissue endocannabinoid levels by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) inhibitors can prevent airway inflammation and hyperreactivity. In this study, the changes in the levels of major metabolites of endocannabinoids by systemic and local FAAH or MAGL inhibitor treatments were evaluated. Mice were treated with either the FAAH inhibitor URB597 or the MAGL inhibitor JZL184 by local (intranasal) or systemic (intraperitoneal) application. Bronchoalveolar lavage (BAL) fluids and lungs were isolated afterward in order to perform histopathological and metabolomic analyses. There were no significant histopathological changes in the lungs and neutrophil, and macrophage and lymphocyte numbers in BAL fluid were not altered after local and systemic treatments. However, GC-MS-based metabolomics profile allowed us to identify 102 metabolites in lung samples, among which levels of 75 metabolites were significantly different from the control. The metabolites whose levels were changed by treatments were mostly related to the endocannabinoid system and energy metabolism. Therefore, these changes may contribute to the anti-inflammatory effects of URB597 and JZL184 treatments in mice.

Palmitoleoylethanolamide Is an Efficient Anti-Obesity Endogenous Compound: Comparison with Oleylethanolamide in Diet-Induced Obesity

Obesity is currently a major epidemic in the developed world. However, we lack a wide range of effective pharmacological treatments and therapies against obesity, and those approved are not devoid of adverse effects. Dietary components such as palmitoleic acid have been proposed to improve metabolic disbalance in obesity, although the mechanisms involved are not well understood. Both palmitoleic acid (POA) and oleic acid (OA) can be transformed in N-acylethanolamines (NAEs), mediating the effects of dietary POA and OA. To test this hypothesis, here, we study the effects on food intake and body weight gain of palmitoleylethanolamide (POEA) and the OA-derived NAE analogue, oleoylethanolamide (OEA), in Sprague-Dawley rats with a hypercaloric cafeteria diet (HFD). Plasma biochemical metabolites, inflammatory mediators, and lipogenesis-associated liver protein expression were also measured. The results indicate that POEA is able to improve health status in diet-induced obesity, decreasing weight, liver steatosis, inflammation, and dyslipemia. The action of POEA was found to be almost identical to that of OEA, which is an activator of the nuclear peroxisome proliferator receptor alpha (PPARα), and it is structurally related to POEA. These results suggest that the dietary administration of either POA or POEA might be considered as nutritional intervention as complementary treatment for complicated obesity in humans.

Jejunal mucosa proteomics unravel metabolic adaptive processes to mild chronic heat stress in dairy cows

Climate change affects the duration and intensity of heat waves during summer months and jeopardizes animal health and welfare. High ambient temperatures cause heat stress in dairy cows resulting in a reduction of milk yield, feed intake, and alterations in gut barrier function. The objectives of this study were to investigate the mucosal amino acid, glucose and lactate metabolism, as well as the proteomic response of the small intestine in heat stressed (HS) Holstein dairy cows. Cows of the HS group (n = 5) were exposed for 4 days to 28 °C (THI = 76) in a climate chamber. Percentage decrease in daily ad libitum intake of HS cows was calculated to provide isocaloric energy intake to pair-fed control cows kept at 15 °C (THI = 60) for 4 days. The metabolite, mRNA and proteomic analyses revealed that HS induced incorrect protein folding, cellular destabilization, increased proteolytic degradation and protein kinase inhibitor activity, reduced glycolysis, and activation of NF-κB signaling, uronate cycling, pentose phosphate pathway, fatty acid and amino acid catabolism, mitochondrial respiration, ATPase activity and the antioxidative defence system. Our results highlight adaptive metabolic and immune mechanisms attempting to maintain the biological function in the small intestine of heat-stressed dairy cows.

Cannabinoid Receptors in Metabolic Regulation and Diabetes

There is an urgent need for developing effective drugs to combat the obesity and Type 2 diabetes mellitus epidemics. The endocannabinoid system plays a major role in energy homeostasis. It comprises the cannabinoid receptors 1 and 2 (CB₁ and CB₂), endogenous ligands called endocannabinoids and their metabolizing enzymes. Because the CB₁ receptor is overactivated in metabolic alterations, pharmacological blockade of the CB₁ receptor arose as a promising candidate to treat obesity. However, because of the wide distribution of CB₁ receptors in the central nervous system, their negative central effects halted further therapeutic use. Although the CB₂ receptor is mostly peripherally expressed, its role in metabolic homeostasis remains unclear. This review discusses the potential of CB₁ and CB₂ receptors at the peripheral level to be therapeutic targets in metabolic diseases. We focus on the impact of pharmacological intervention and/or silencing on peripheral cannabinoid receptors in organs/tissues relevant for energy homeostasis. Moreover, we provide a perspective on novel therapeutic strategies modulating these receptors. Targeting CB₁ with peripherally restricted antagonists, neutral antagonists, inverse agonists, or monoclonal antibodies could represent successful strategies. CB₂ agonism has shown promising results at preclinical level. Beyond classic antagonism and agonism targeting orthosteric sites, the recently described crystal structures of CB₁ and CB₂ open new possibilities for therapeutic interventions with negative and positive allosteric modulators. The challenge of simultaneously targeting CB₁ and CB₂ might be possible by developing dual-steric ligands. The future will tell whether these promising strategies result in a renaissance of the cannabinoid receptors as therapeutic targets in metabolic diseases.

Cannabinoid Receptors: An Update on Cell Signaling, Pathophysiological Roles and Therapeutic Opportunities in Neurological, Cardiovascular, and Inflammatory Diseases

The identification of the human cannabinoid receptors and their roles in health and disease, has been one of the most significant biochemical and pharmacological advancements to have occurred in the past few decades. In spite of the major strides made in furthering endocannabinoid research, therapeutic exploitation of the endocannabinoid system has often been a challenging task. An impaired endocannabinoid tone often manifests as changes in expression and/or functions of type 1 and/or type 2 cannabinoid receptors. It becomes important to understand how alterations in cannabinoid receptor cellular signaling can lead to disruptions in major physiological and biological functions, as they are often associated with the pathogenesis of several neurological, cardiovascular, metabolic, and inflammatory diseases. This review focusses mostly on the pathophysiological roles of type 1 and type 2 cannabinoid receptors, and it attempts to integrate both cellular and physiological functions of the cannabinoid receptors. Apart from an updated review of pre-clinical and clinical studies, the adequacy/inadequacy of cannabinoid-based therapeutics in various pathological conditions is also highlighted. Finally, alternative strategies to modulate endocannabinoid tone, and future directions are also emphasized.

Acute and short-term administrations of delta-9-tetrahydrocannabinol modulate major gut metabolomic regulatory pathways in C57BL/6 mice

Delta-9-tetrahydrocannabinol (THC) is the primary psychoactive compound in Cannabis, which is studied extensively for its medicinal value. A central gap in the science is the underlying mechanisms surrounding THC's therapeutic effects and the role of gut metabolite profiles. Using a mass-spectrometry based metabolomics, we show here that intraperitoneal injection of THC in C57BL/6 mice modulates metabolic profiles that have previously been identified as integral to health. Specifically, we investigated the effects of acute (single THC injection denoted here as '1X') and short -term (five THC injections on alternate days denoted as '5X') THC administration on fecal and intestinal tissue metabolite profiles. Results are consistent with the hypothesis that THC administration alters host metabolism by targeting two prominent lipid metabolism pathways: glycerophospholipid metabolism and fatty acid biosynthesis.

Role of Cannabinoid Receptor Type 1 in Insulin Resistance and Its Biological Implications

Endogenous cannabinoids (ECs) are lipid-signaling molecules that specifically bind to cannabinoid receptor types 1 and 2 (CB1R and CB2R) and are highly expressed in central and many peripheral tissues under pathological conditions. Activation of hepatic CB1R is associated with obesity, insulin resistance, and impaired metabolic function, owing to increased energy intake and storage, impaired glucose and lipid metabolism, and enhanced oxidative stress and inflammatory responses. Additionally, blocking peripheral CB1R improves insulin sensitivity and glucose metabolism and also reduces hepatic steatosis and body weight in obese mice. Thus, targeting EC receptors, especially CB1R, may provide a potential therapeutic strategy against obesity and insulin resistance. There are many CB1R antagonists, including inverse agonists and natural compounds that target CB1R and can reduce body weight, adiposity, and hepatic steatosis, and those that improve insulin sensitivity and reverse leptin resistance. Recently, the use of CB1R antagonists was suspended due to adverse central effects, and this caused a major setback in the development of CB1R antagonists. Recent studies, however, have focused on development of antagonists lacking adverse effects. In this review, we detail the important role of CB1R in hepatic insulin resistance and the possible underlying mechanisms, and the therapeutic potential of CB1R targeting is also discussed.

High Fat Diet Increases Circulating Endocannabinoids Accompanied by Increased Synthesis Enzymes in Adipose Tissue

The endocannabinoid system (ECS) controls energy balance by regulating both energy intake and energy expenditure. Endocannabinoid levels are elevated in obesity suggesting a potential causal relationship. This study aimed to elucidate the rate of dysregulation of the ECS, and the metabolic organs involved, in diet-induced obesity. Eight groups of age-matched male C57Bl/6J mice were randomized to receive a chow diet (control) or receive a high fat diet (HFD, 45% of calories derived from fat) ranging from 1 day up to 18 weeks before euthanasia. Plasma levels of the endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide (N-arachidonoylethanolamine, AEA), and related N-acylethanolamines, were quantified by UPLC-MS/MS and gene expression of components of the ECS was determined in liver, muscle, white adipose tissue (WAT) and brown adipose tissue (BAT) during the course of diet-induced obesity development. HFD feeding gradually increased 2-AG (+132% within 4 weeks, P < 0.05), accompanied by upregulated expression of its synthesizing enzymes Daglα and β in WAT and BAT. HFD also rapidly increased AEA (+81% within 1 week, P < 0.01), accompanied by increased expression of its synthesizing enzyme Nape-pld, specifically in BAT. Interestingly, Nape-pld expression in BAT correlated with plasma AEA levels (R ² = 0.171, β = 0.276, P < 0.001). We conclude that a HFD rapidly activates adipose tissue depots to increase the synthesis pathways of endocannabinoids that may aggravate the development of HFD-induced obesity.

Dicarbonyl Stress and Glyoxalase-1 in Skeletal Muscle: Implications for Insulin Resistance and Type 2 Diabetes

Glyoxalase-1 (GLO1) is a ubiquitously expressed cytosolic protein which plays a role in the natural maintenance of cellular health and is abundantly expressed in human skeletal muscle. A consequence of reduced GLO1 protein expression is cellular dicarbonyl stress, which is elevated in obesity, insulin resistance and type 2 diabetes (T2DM). Both in vitro and pre-clinical models suggest dicarbonyl stress per se induces insulin resistance and is prevented by GLO1 overexpression, implicating a potential role for GLO1 therapy in insulin resistance and type 2 diabetes (T2DM). Recent work has identified the therapeutic potential of novel natural agents as a GLO1 inducer, which resulted in improved whole-body metabolism in obese adults. Given skeletal muscle is a major contributor to whole-body glucose, lipid, and protein metabolism, such GLO1 inducers may act, in part, through mechanisms in skeletal muscle. Currently, investigations examining the specificity of dicarbonyl stress and GLO1 biology in human skeletal muscle are lacking. Recent work from our lab indicates that dysregulation of GLO1 in skeletal muscle may underlie human insulin resistance and that exercise training may impart therapeutic benefits. This minireview will summarize the existing human literature examining skeletal muscle GLO1 and highlight the emerging therapeutic concepts for GLO1 gain-of-function in conditions such as insulin resistance and cardiometabolic disease.

Utilizing Optimized Tools to Investigate PTM Crosstalk: Identifying Potential PTM Crosstalk of Acetylated Mitochondrial Proteins

Post-translational modification (PTM) crosstalk is recognized as a major cell-regulatory mechanism, and studies of several proteins have validated the premise that PTMs work in concert. Previous work by our group investigated the potential PTM crosstalk on proteins in the EGFR-Ras-c-Fos axis by utilizing a comprehensive set of PTM reagents termed Signal-Seeker toolkits. In this study, these tools were used to investigate the potential PTM crosstalk that occurs in acetylated mitochondrial proteins in response to a mitochondrial stress-inducing agent hydrogen peroxide (H₂O₂). Mitochondrial protein acetylation has been shown to participate in PTM crosstalk as exemplified by the regulation of the pyruvate dehydrogenase complex via kinase, phosphatase, acetyltransferase, and deacetylase activities. Changes in the acetylated state of mitochondrial proteins were investigated, in response to H₂O₂, using a novel anti acetyl lysine (Ac-K) antibody. Signal-Seeker PTM detection tools were used to validate the acetylation state of ten mitochondrial targets, as well as their endogenous acetylation state in response to H₂O₂. Importantly, the endogenous acetylation, ubiquitination, SUMOylation 2/3, and tyrosine phosphorylation state of four target mitochondrial proteins were also investigated with the toolkit. Each of the four proteins had unique PTM profiles, but diverging acetylation and ubiquitin or SUMO 2/3 signals appeared to be a common theme. This proof-of-concept study identifies the Signal-Seeker toolkits as a useful tool to investigate potential PTM crosstalk.

Cooperative role of the glucagon-like peptide-1 receptor and β3-adrenergic-mediated signalling on fat mass reduction through the downregulation of PKA/AKT/AMPK signalling in the adipose tissue and muscle of rats

AIM

To explore the cooperation of GLP-1 receptor and β3-adrenergic receptor (β3-AR)-mediated signalling in the control of fat mass/feeding behaviour by studying the effects of a combined therapy composed of the GLP-1R agonist liraglutide and the β3-AR agonist CL316243.

METHODS

The study included the analysis of key mechanisms regulating lipid/cholesterol metabolism, and thermogenesis in brown (BAT) and epididymal white (eWAT) adipose tissues, abdominal muscle and liver of male rats.

RESULTS

CL316243 (1 mg kg^-1 ) and liraglutide (100 μg kg^-1 ) co-administration over 6 days potentiated an overall negative energy balance (reduction in food intake, body weight gain, fat/non-fat mass ratio, liver fat content, and circulating levels of non-essential fatty acids, triglycerides, very low-density lipoprotein-cholesterol and leptin). These effects were accompanied by increased plasma levels of insulin and IL6. We also observed increased gene expression of uncoupling proteins regulating thermogenesis in BAT/eWAT (Ucp1) and muscle (Ucp2/3). Expression of transcription factor and enzymes involved either in de novo lipogenesis (Chrebp, Acaca, Fasn, Scd1, Insig1, Srebp1) or in fatty acid β-oxidation (Cpt1b) was enhanced in eWAT and/or muscle but decreased in BAT. Pparα and Pparγ, essentials in lipid flux/storage, were decreased in BAT/eWAT but increased in the muscle and liver. Cholesterol synthesis regulators (Insig2, Srebp2, Hmgcr) were particularly over-expressed in muscle. These GLP-1R/β3-AR-induced metabolic effects were associated with the downregulation of cAMP-dependent signalling pathways (PKA/AKT/AMPK).

CONCLUSION

Combined activation of GLP-1 and β3-ARs potentiate changes in peripheral pathways regulating lipid/cholesterol metabolism in a tissue-specific manner that favours a switch in energy availability/expenditure and may be useful for obesity treatment.

Localization of the cannabinoid type-1 receptor in subcellular astrocyte compartments of mutant mouse hippocampus

Astroglial type-1 cannabinoid (CB₁ ) receptors are involved in synaptic transmission, plasticity and behavior by interfering with the so-called tripartite synapse formed by pre- and post-synaptic neuronal elements and surrounding astrocyte processes. However, little is known concerning the subcellular distribution of astroglial CB₁ receptors. In particular, brain CB₁ receptors are mostly localized at cells' plasmalemma, but recent evidence indicates their functional presence in mitochondrial membranes. Whether CB₁ receptors are present in astroglial mitochondria has remained unknown. To investigate this issue, we included conditional knock-out mice lacking astroglial CB₁ receptor expression specifically in glial fibrillary acidic protein (GFAP)-containing astrocytes (GFAP-CB₁ -KO mice) and also generated genetic rescue mice to re-express CB₁ receptors exclusively in astrocytes (GFAP-CB₁ -RS). To better identify astroglial structures by immunoelectron microscopy, global CB₁ knock-out (CB₁ -KO) mice and wild-type (CB₁ -WT) littermates were intra-hippocampally injected with an adeno-associated virus expressing humanized renilla green fluorescent protein (hrGFP) under the control of human GFAP promoter to generate GFAPhrGFP-CB₁ -KO and -WT mice, respectively. Furthermore, double immunogold (for CB₁ ) and immunoperoxidase (for GFAP or hrGFP) revealed that CB₁ receptors are present in astroglial mitochondria from different hippocampal regions of CB₁ -WT, GFAP-CB₁ -RS and GFAPhrGFP-CB₁ -WT mice. Only non-specific gold particles were detected in mouse hippocampi lacking CB₁ receptors. Altogether, we demonstrated the existence of a precise molecular architecture of the CB₁ receptor in astrocytes that will have to be taken into account in evaluating the functional activity of cannabinergic signaling at the tripartite synapse.

The CB1 Receptor as the Cornerstone of Exostasis

The type-1 cannabinoid receptor (CB1) is the main effector of the endocannabinoid system (ECS), which is involved in most brain and body functions. In this Perspective, we provide evidence indicating that CB1 receptor functions are key determinants of bodily coordinated exostatic processes. First, we will introduce the concepts of endostasis and exostasis as compensation or accumulation for immediate or future energy needs and discuss how exostasis has been necessary for the survival of species during evolution. Then, we will argue how different specific biological functions of the CB1 receptor in the body converge to provide physiological exostatic processes. Finally, we will introduce the concept of proactive evolution-induced diseases (PEIDs), which helps explain the seeming paradox that an evolutionary-selected physiological function can become the cause of epidemic pathological conditions, such as obesity. We propose here a possible unifying theory of CB1 receptor functions that can be tested by future experimental studies.

Cannabinoid signaling in health and disease

Cannabis sativa has long been used for medicinal purposes. To improve safety and efficacy, compounds from C. sativa were purified or synthesized and named under an umbrella group as cannabinoids. Currently, several cannabinoids may be prescribed in Canada for a variety of indications such as nausea and pain. More recently, an increasing number of reports suggest other salutary effects associated with endogenous cannabinoid signaling including cardioprotection. The therapeutic potential of cannabinoids is therefore extended; however, evidence is limited and mechanisms remain unclear. In addition, the use of cannabinoids clinically has been hindered due to pronounced psychoactive side effects. This review provides an overview on the endocannabinoid system, including known physiological roles, and conditions in which cannabinoid receptor signaling has been implicated.

Cannabinoid CB1 Receptors Are Localized in Striated Muscle Mitochondria and Regulate Mitochondrial Respiration

The cannabinoid type 1 (CB₁) receptor is widely distributed in the brain and peripheral organs where it regulates cellular functions and metabolism. In the brain, CB₁ is mainly localized on presynaptic axon terminals but is also found on mitochondria (mtCB₁), where it regulates cellular respiration and energy production. Likewise, CB₁ is localized on muscle mitochondria, but very little is known about it. The aim of this study was to further investigate in detail the distribution and functional role of mtCB₁ in three different striated muscles. Immunoelectron microscopy for CB₁ was used in skeletal muscles (gastrocnemius and rectus abdominis) and myocardium from wild-type and CB₁-KO mice. Functional assessments were performed in mitochondria purified from the heart of the mice and the mitochondrial oxygen consumption upon application of different acute delta-9-tetrahydrocannabinol (Δ⁹-THC) concentrations (100 nM or 200 nM) was monitored. About 26% of the mitochondrial profiles in gastrocnemius, 22% in the rectus abdominis and 17% in the myocardium expressed CB₁. Furthermore, the proportion of mtCB1 versus total CB₁ immunoparticles was about 60% in the gastrocnemius, 55% in the rectus abdominis and 78% in the myocardium. Importantly, the CB₁ immunolabeling pattern disappeared in muscles of CB₁-KO mice. Functionally, acute 100 nM or 200 nM THC treatment specifically decreased mitochondria coupled respiration between 12 and 15% in wild-type isolated mitochondria of myocardial muscles but no significant difference was noticed between THC treated and vehicle in mitochondria isolated from CB₁-KO heart. Furthermore, gene expression of key enzymes involved in pyruvate synthesis, tricarboxylic acid (TCA) cycle and mitochondrial respiratory chain was evaluated in the striated muscle of CB₁-WT and CB₁-KO. CB₁-KO showed an increase in the gene expression of Eno3, Pkm2, and Pdha1, suggesting an increased production of pyruvate. In contrast, no significant difference was observed in the Sdha and Cox4i1 expression, between CB₁-WT and CB₁-KO. In conclusion, CB₁ receptors in skeletal and myocardial muscles are predominantly localized in mitochondria. The activation of mtCB₁ receptors may participate in the mitochondrial regulation of the oxidative activity probably through the relevant enzymes implicated in the pyruvate metabolism, a main substrate for TCA activity.

Cannabinoid receptor type-1: breaking the dogmas

The endocannabinoid system (ECS) is abundantly expressed in the brain. This system regulates a plethora of physiological functions and is composed of cannabinoid receptors, their endogenous ligands (endocannabinoids), and the enzymes involved in the metabolism of endocannabinoids. In this review, we highlight the new advances in cannabinoid signaling, focusing on a key component of the ECS, the type-1 cannabinoid receptor (CB ₁). In recent years, the development of new imaging and molecular tools has demonstrated that this receptor can be distributed in many cell types (e.g., neuronal or glial cells) and intracellular compartments (e.g., mitochondria). Interestingly, cellular and molecular effects are differentially mediated by CB ₁ receptors according to their specific localization (e.g., glutamatergic or GABAergic neurons). Moreover, this receptor is expressed in the periphery, where it can modulate periphery-brain connections. Finally, the better understanding of the CB ₁ receptor structure led researchers to propose interesting and new allosteric modulators. Thus, the advances and the new directions of the CB ₁ receptor field will provide new insights and better approaches to profit from its interesting therapeutic profile.