Cocaine- and amphetamine-regulated transcript (CART) peptide: a vasoactive role in the cerebral circulation

CARTp/GPR160 mediates behavioral hypersensitivities in mice through NOD2

ABSTRACT

Neuropathic pain is a debilitating chronic condition that remains difficult to treat. More efficacious and safer therapeutics are needed. A potential target for therapeutic intervention recently identified by our group is the G-protein coupled receptor 160 (GPR160) and the cocaine- and amphetamine-regulated transcript peptide (CARTp) as a ligand for GPR160. Intrathecal administration of CARTp in rodents causes GPR160-dependent behavioral hypersensitivities. However, the molecular and biochemical mechanisms underpinning GPR160/CARTp-induced behavioral hypersensitivities in the spinal cord remain poorly understood. Therefore, we performed an unbiased RNA transcriptomics screen of dorsal horn spinal cord (DH-SC) tissues harvested at the time of peak CARTp-induced hypersensitivities and identified nucleotide-binding oligomerization domain-containing protein 2 (Nod2) as a gene that is significantly upregulated. Nucleotide-binding oligomerization domain-containing protein 2 is a cytosolic pattern-recognition receptor involved in activating the immune system in response to bacterial pathogens. While NOD2 is well studied under pathogenic conditions, the role of NOD2-mediated responses in nonpathogenic settings is still not well characterized. Genetic and pharmacological approaches reveal that CARTp-induced behavioral hypersensitivities are driven by NOD2, with co-immunoprecipitation studies indicating an interaction between GPR160 and NOD2. Cocaine- and amphetamine-regulated transcript peptide-induced behavioral hypersensitivities are independent of receptor-interacting protein kinase 2 (RIPK2), a common adaptor protein to NOD2. Immunofluorescence studies found NOD2 co-expressed with endothelial cells rather than glial cells, implicating potential roles for CARTp/NOD2 signaling in these cells. While these findings are based only on studies with male mice, our results identify a novel pathway by which CARTp causes behavioral hypersensitivities in the DH-SC through NOD2 and highlights the importance of NOD2-mediated responses in nonpathogenic settings.

Unique, Specific CART Receptor-Independent Regulatory Mechanism of CART(55-102) Peptide in Spinal Nociceptive Transmission and Its Relation to Dipeptidyl-Peptidase 4 (DDP4)

Cocaine- and amphetamine-regulated transcript (CART) peptides are involved in several physiological and pathological processes, but their mechanism of action is unrevealed due to the lack of identified receptor(s). We provided evidence for the antihyperalgesic effect of CART(55-102) by inhibiting dipeptidyl-peptidase 4 (DPP4) in astrocytes and consequently reducing neuroinflammation in the rat spinal dorsal horn in a carrageenan-evoked inflammation model. Both naturally occurring CART(55-102) and CART(62-102) peptides are present in the spinal cord. CART(55-102) is not involved in acute nociception but regulates spinal pain transmission during peripheral inflammation. While the full-length peptide with a globular motif contributes to hyperalgesia, its N-terminal inhibits this process. Although the anti-hyperalgesic effects of CART(55-102), CART(55-76), and CART(62-76) are blocked by opioid receptor antagonists in our inflammatory models, but not in neuropathic Seltzer model, none of them bind to any opioid or G-protein coupled receptors. DPP4 interacts with Toll-like receptor 4 (TLR4) signalling in spinal astrocytes and enhances the TLR4-induced expression of interleukin-6 and tumour necrosis factor alpha contributing to inflammatory pain. Depending on the state of inflammation, CART(55-102) is processed in the spinal cord, resulting in the generation of biologically active isoleucine-proline-isoleucine (IPI) tripeptide, which inhibits DPP4, leading to significantly decreased glia-derived cytokine production and hyperalgesia.

Endocrine Disruptor Bisphenol a Affects the Neurochemical Profile of Nerve Fibers in the Aortic Arch Wall in the Domestic Pig

Bisphenol A (BPA) is a synthetic compound utilized in industry for the production of various plastics. BPA penetrates into the environment and adversely affects living organisms. Therefore, the influence of various BPA dosages on the neurochemical characteristics of nerve fibers located in the aortic branch wall was investigated in this study utilizing a double immunofluorescence method. It was found that BPA in concentration of 0.5 mg/kg body weight/day causes a clear increase in the density of nerves within aortic branch walls immunoreactive to cocaine- and amphetamine-regulated transcript (CART), calcitonin gene-related peptide (CGRP), neuronal isoform of nitric oxide synthase (nNOS), pituitary adenylate cyclase-activating peptide (PACAP), and vasoactive intestinal polypeptide (VIP). Nerves containing galanin (GAL) and/or somatostatin (SOM) did not change when BPA was introduced into the system. Changes noted after administration of BPA at a dose of 0.05 mg/kg body weight/day were less visible and concerned fibers immunoreactive to CART, CGRP, and/or PACAP. The obtained results show that BPA affects the neurochemical coding of nerves in the aortic branch wall. These fluctuations may be the first signs of the influence of this substance on blood vessels and may also be at the root of the disturbances in the cardiovascular system.

Aqueous humor proteomic analysis of acute angle-closure glaucoma with visual field loss

Background

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency that occurs over the course of hours or days and may cause irreversible blindness if not treated immediately. In most cases, optic nerve damage is the cause of visual field (VF) loss in AACG. There has been no reliable biomarker found to evaluate optic nerve damage to date. Aqueous humor (AH) proteome analysis might reveal the proteomic alterations in AACG and provide helpful clues in the search for an AH biomarker of optic nerve damage and VF loss.

Methods

In this study, we used the AH proteome to explore the functions of differentially expressed proteins (DEPs) during disease progression. The AH proteins from the early-stage group and late-stage group were extracted and analyzed by the data-independent acquisition (DIA) method. The DEPs functions were annotated, and parallel reaction monitoring (PRM) was used to validate the key DEPs.

Results

A total of 87 DEPs were found. Gene Ontology analysis showed that most DEPs were enriched in immunology, hemodynamics, and apoptosis. Ingenuity pathway analysis found that vascular endothelial growth factor (VEGF) signaling, the production of reactive oxygen species (ROS) in macrophages, and the nuclear factor erythroid 2-related factor 2 (NRF2)-mediated oxidative stress response were active pathways in the late stage of AACG. The mechanism of retinal ganglion cell (RGC) death was hypothesized on the basis of DEP functional analysis. A total of 20 DEPs were validated by using PRM, and prostaglandin-H2 D-isomerase was found to have the potential to evaluate optic nerve damage.

Conclusions

This study showed that AH proteomic analysis could reveal the proteomic alterations in the pathogenesis of VF loss in AACG and help to provide objective protein biomarkers to evaluate VF loss. These findings will benefit the application of the AH proteome to clinical research.

CART decreases islet blood flow, but has no effect on total pancreatic blood flow and glucose tolerance in anesthetized rats

Cocaine- and amphetamine-regulated transcript (CART) is a neurotransmitter and hormone, involved in the regulation of e.g. food intake, body weight, reward and addiction, and stress response. CART has also been found to affect insulin secretion and beta cell morphology, both in vivo and in vitro. Furthermore, CART affects regulation of the cardiovascular system and helps to modulate vascular tone. The present study evaluated the local effect of CART on the pancreatic and islet circulation and function. CART (25 μg/h) or saline, combinations of CART and endothelin-A receptor antagonist (BQ123; 100 μg/kg), and glucose (2 g/kg) were intravenously infused in Sprague Dawley rats followed by blood flow measurements using a microsphere technique. Separately, CART-infused animals underwent an intravenous glucose tolerance test (ivGTT). The direct effect of CART on insulin release was investigated using isolated islets from Sprague Dawley rats. CART reduced islet blood flow, without reduction in total pancreatic blood flow. The normal glucose-induced islet blood flow increase was diminished by CART, albeit still present. Simultaneously, CART had no effect on systemic-, intestinal- or renal blood flow. The endothelin-A receptor antagonist BQ123 together with CART had no pancreatic vascular effects. We found that CART has pronounced vascular constrictive actions restricted to the pancreatic islet circulation but had no effect on insulin release neither in vivo nor in vitro. The mechanisms behind the vascular effects are still unknown, but may reflect a direct action on pancreatic blood vessels.

An Immunohistochemical Study of Cocaine- and Amphetamine-Regulated Transcript (Cart) Expression in the Pterygopalatine Ganglion of the Pig

Although, a great effort has been made to understand the synthesis, regulation, processing and function of cocaine- and amphetamine-regulated transcript (CART) peptide at the central level, its peripheral function(s) are still obscure. Moreover, scarce studies describing the presence of CART in peripheral autonomic ganglia are mainly limited to laboratory rodents. Thus, the aim of the present study was to immunohistochemically investigate the expression of CART in Hu C/D-positive neurons of the porcine pterygopalatine ganglion (PPG). The distribution pattern of CART-IR nerve elements in PPG has been also assessed. The co-localization of CART with substance P (SP), galanin or somatostatin was studied by means of double immunohistochemical stainings. The presence of Hu C/D-positive/CART-positive neurons was detected both in the left and right PPG (4.7±1.2% and 5.2% ± 1.4%, respectively). The CARTimmunoreactive (IR) neurons were categorized as either middle (ca. 80%) or small (ca. 20%) in size. Moderate numbers of CART-IR boutons were also detected between CART-negative ganglionic neurons. CART-IR basket-like formations around PPG neurons were regularly observed. Virtually all CART-IR neurons additionally co-stored VIP, whereas none of the CART-expressing cells showed the presence of galanin, SP or somatostatin. CART-IR basket-like formations exclusively encircled VIP-IR PPG neurons. Thus, CART-IR nerve cells seem to constitute a relatively small homologous population of the porcine PPG neurons with largely unknown functions. Further functional studies aiming at whether CART-IR neurons could serve as interneurons are necessary.

Post-treatment with cocaine- and amphetamine-regulated transcript enhances infarct resolution, reinnervation, and angiogenesis in stroke rats - an MRI study

Recent studies have shown that post-treatment with cocaine- and amphetamine-regulated transcript (CART) has neuroregenerative effects in animal models of stroke. The purpose of this study was to characterize CART-mediated neuronal and vascular repairments using non-invasive MRI techniques. Adult male rats were subjected to a 90 min middle cerebral artery occlusion (MCAo). Animals were separated into two groups with similar infarction sizes, measured by T2 -weighted MRI on Day 2 after MCAo, and were treated with CART or vehicle intranasally from Day 3 to Day 12. Diffusion tensor imaging was used to examine changes in plasticity of white matter elements. Susceptibility-weighted imaging (SWI) was used to measure angiogenesis. Post-treatment with CART significantly increased fractional anisotropy (FA) in lesioned cortex on Days 10 and 25 post stroke. A significant correlation between the behavioral recovery in body asymmetry and the change in FA was shown, suggesting that behavioral recovery was associated with reinnervation to the lesioned hemisphere. CART also increased the intensity of SWI and the immunoreactivity of the vascular marker alpha-smooth muscle actin in lesioned cortex. Together, our data support a non-invasive treatment strategy for stroke through angiogenesis and reinnervation by CART. Copyright © 2016 John Wiley & Sons, Ltd.

Methamphetamine induces the release of endothelin

Methamphetamine is a potent psychostimulant drug of abuse that increases release and blocks reuptake of dopamine, producing intense euphoria, factors that may contribute to its widespread abuse. It also produces severe neurotoxicity resulting from oxidative stress, DNA damage, blood-brain barrier disruption, microgliosis, and mitochondrial dysfunction. Intracerebral hemorrhagic and ischemic stroke have been reported after intravenous and oral abuse of methamphetamine. Several studies have shown that methamphetamine causes vasoconstriction of vessels. This study investigates the effect of methamphetamine on endothelin-1 (ET-1) release in mouse brain endothelial cells by ELISA. ET-1 transcription as well as endothelial nitric oxide synthase (eNOS) activation and transcription were measured following methamphetamine treatment. We also examine the effect of methamphetamine on isolated cerebral arteriolar vessels from C57BL/6 mice. Penetrating middle cerebral arterioles were cannulated at both ends with a micropipette system. Methamphetamine was applied extraluminally, and the vascular response was investigated. Methamphetamine treatment of mouse brain endothelial cells resulted in ET-1 release and a transient increase in ET-1 message. The activity and transcription of eNOS were only slightly enhanced after 24 hr of treatment with methamphetamine. In addition, methamphetamine caused significant vasoconstriction of isolated mouse intracerebral arterioles. The vasoconstrictive effect of methamphetamine was attenuated by coapplication of the endothelin receptor antagonist PD145065. These findings suggest that vasoconstriction induced by methamphetamine is mediated through the endothelin receptor and may involve an endothelin-dependent pathway.

Quantitative evaluation of CART-containing cells in urinary bladder of rats with renovascular hypertension

Recent biological advances make it possible to discover new peptides associated with hypertension. The cocaine- and amphetamine-regulated transcript (CART) is a known factor in appetite and feeding behaviour. Various lines of evidence suggest that this peptide participates not only in control of feeding behaviour but also in the regulation of the cardiovascular and sympathetic systems and blood pressure. The role of CART in blood pressure regulation led us to undertake a study aimed at analysing quantitative changes in CART-containing cells in urinary bladders (UB) of rats with renovascular hypertension. We used the Goldblatt model of arterial hypertension (two-kidney, one clip) to evaluate quantitative changes. This model provides researchers with a commonly used tool to analyse the renin-angiotensin system of blood pressure control and, eventually, to develop drugs for the treatment of chronic hypertension. The study was performed on sections of urinary bladders of rats after 3-, 14-, 28-, 42 and 91 days from hypertension induction. Immunohistochemical identification of CART cells was performed on paraffin for the UBs of all the study animals. CART was detected in the endocrine cells, especially numerous in the submucosa and muscularis layers, with a few found in the transitional epithelium and only occasionally in serosa. Hypertension significantly increased the number of CART-positive cells in the rat UBs. After 3 and 42 days following the procedure, statistically significantly higher numbers of CART-positive cells were identified in comparison with the control animals. The differences between the hypertensive rats and the control animals concerned not only the number density of CART-immunoreactive cells but also their localization. After a 6-week period, each of the rats subjected to the renal artery clipping procedure developed stable hypertension. CART appeared in numerous transitional epithelium cells.

As this study provides novel findings, the question appears about the type of connection between hypertension and the functioning and activity of CART in the urinary tract (UT). The study gives rise to the assumption that high blood pressure can be a factor that intensifies CART secretion. In conclusion, the endocrine system of the urinary tract is modified by renovascular hypertension. This may affect the production of hormones and biologically active substances and contribute to the development of possible hypertension complications. In order to fully comprehend the role of the CART peptide in blood pressure regulation, further analyses are necessary.

Quantitative and qualitative evaluation of CART-containing cells in adrenal glands of male rats with hypertension

Adrenal activity is stimulated and secretion of stress hormones is increased during advanced stages of renovascular hypertension. The literature suggests that the neuropeptide, cocaine and amphetamine regulated transcript (CART), might regulate adrenal secretory function and thus could influence its activity. We assessed potential quantitative and qualitative changes in the cells that contained CART in the adrenal glands of rats with renovascular hypertension. The renal arteries of ten rats were subjected to a clipping procedure, i.e., two-kidney one-clip (2K1C) model of arterial hypertension, and after 6 weeks each rat developed stable hypertension. CART was localized using immunohistochemistry. CART was detected in a large population of cells in the medulla, sparse nerve fibers in the cortex and the capsule of the adrenal gland. The population of CART-positive cells in adrenal glands of two kidney-one clip (2K1C) treated rats was greater and their immunoreactivity was increased compared to controls. Similarly, the length, width, area and diameter of CART-immunoreactive cells were significantly greater in the hypertensive rats than in controls. We demonstrated that renovascular hypertension alters the number and immunoreactivity of CART-containing cells in adrenal glands.

Gender-specific increase of bone mass by CART peptide treatment is ovary-dependent

Cocaine- and amphetamine-regulated transcript (CART) has emerged as a neurotransmitter and hormone that has been implicated in many processes including food intake, maintenance of body weight, and reward, but also in the regulation of bone mass. CART-deficient mice are characterized by an osteoporotic phenotype, whereas female transgenic mice overexpressing CART display an increase in bone mass. Here we describe experiments that show that peripheral subcutaneous sustained release of different CART peptide isoforms for a period up to 60 days increased bone mass by 80% in intact mice. CART peptides increased trabecular bone mass, but not cortical bone mass, and the increase was caused by reduced osteoclast activity in combination with normal osteoblast activity. The observed effect on bone was gender-specific, because male mice did not respond to treatment with CART peptides. In addition, male transgenic CART overexpressing mice did not display increased bone mass. Ovariectomy (OVX) completely abolished the increase of bone mass by CART peptides, both in CART peptide-treated wild-type mice and in CART transgenic mice. The effect of CART peptide treatment on trabecular bone was not mediated by 17β-estradiol (E(2)) because supplementation of OVX mice with E(2) could not rescue the effect of CART peptides on bone. Together, these results indicate that sustained release of CART peptides increases bone mass in a gender-specific way via a yet unknown mechanism that requires the presence of the ovary.

Hypothalamic cocaine- and amphetamine-regulated transcript and corticotrophin releasing factor neurons are stimulated by extracellular volume and osmotic changes

Several studies suggest that hypothalamic cocaine- and amphetamine-regulated transcript (CART) may interact with the hypothalamic-pituitary-adrenal (HPA) axis in the control of neuroendocrine function and may also participate in cardiovascular regulation. Therefore, this study aimed to evaluate, in experimental models of isotonic (I-EVE) and hypertonic (H-EVE) extracellular volume expansion and water deprivation (WD), the activation of CART- and corticotrophin releasing factor (CRF)-immunoreactive neurons, as well as the relative expression of CART and CRF mRNAs in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Both H-EVE (0.30M NaCl, 2mL/100g of body weight, in 1 minute) and 24 hours of WD significantly increased plasma sodium concentrations, producing, respectively, either an increase or a decrease in extracellular volume. I-EVE (0.15M NaCl, 2mL/100g of body weight, in 1 minute) evoked a significant increase in the circulating volume accompanied by unaltered plasma concentrations of sodium. CART-expressing neurons of both magnocellular and parvocellular hypothalamic divisions were activated to produce Fos in response to H-EVE but not in response to I-EVE. Furthermore, increased expression of CART mRNA was found in the PVN of H-EVE but not I-EVE rats. These data show for the first time that EVE not only activates hypothalamic CRF neurons but also increases CRF mRNA expression in the PVN. In contrast, WD increases the number of CART-immunoreactive neurons activated to produce Fos in the PVN and SON but does not change the number of neurons double labeled for Fos and CRF or expression of CRF mRNA in the PVN. These findings provided new insights into the participation of CART in diverse processes within the PVN and SON, including its possible involvement in activation of the HPA axis and cardiovascular regulation in response to changes in extracellular volume and osmolality.

In vivo cerebrovascular effects of cocaine- and amphetamine-regulated transcript (CART) peptide

Cocaine- and amphetamine-regulated transcript (CART) and its associated peptides have been implicated in a number of physiologic processes including modulation of the hypothalamo-pituitary-adrenal (HPA) axis and cardiovascular regulation. Recently, we reported that in isolated cerebral arterioles, CART peptide (CARTp) acts directly to produce endothelium-dependent constriction via the endothelin signaling pathway. We used the rat closed cranial window model to determine the in vivo effects of CARTp on pial arteriolar diameter. Intravenous administration of 30 microg/kg CARTp produced a significant pressor effect and constriction of pial arterioles. The pressor response to systemic CARTp was blocked by the beta-adrenergic receptor antagonist propranolol (2 mg/kg IV). Direct application of 0.1 nM-1 microM CARTp to pial arterioles produced a dose-dependent and long-lasting constriction to approximately 88% of baseline diameter. The constriction response to topically applied 100 nM CARTp was blocked by both the endothelin A (ETA) receptor antagonist BQ-123 (10 microM) and the inhibitor of endothelin-converting enzyme, phosphoramidon (100 nM). These results demonstrate for the first time that CARTp constricts cerebral vessels in vivo, an action mediated by its effects on the endothelin system, specifically via activation of ETA receptors. This supports the notion that CARTp plays a physiologic role in cerebrovascular regulation, particularly during times of HPA axis activation.

CART peptides: regulators of body weight, reward and other functions

Over the past decade or so, CART (cocaine- and amphetamine-regulated transcript) peptides have emerged as major neurotransmitters and hormones. CART peptides are widely distributed in the CNS and are involved in regulating many processes, including food intake and the maintenance of body weight, reward and endocrine functions. Recent studies have produced a wealth of information about the location, regulation, processing and functions of CART peptides, but additional studies aimed at elucidating the physiological effects of the peptides and at characterizing the CART receptor(s) are needed to take advantage of possible therapeutic applications.

CART peptides as modulators of dopamine and psychostimulants and interactions with the mesolimbic dopaminergic system

Cocaine- and amphetamine-regulated transcript (CART) peptides (CART 55-102 and CART 62-102) are peptidergic neurotransmitters that are widely but specifically distributed throughout the brain, gut and other parts of the body. They are found in many brain regions associated with drug addiction including the nucleus accumbens, ventral tegmental area and ventral pallidum. Injections of CART 55-102 into the nucleus accumbens have no effect on basal locomotor activity. However, an injection of CART just before an i.p. injection of cocaine reduces the locomotor activating effects of cocaine. These and other data suggest that CART in the accumbens blunts the effects of cocaine. A hypothesis is that CART is homeostatic in the accumbens and tends to oppose large increases in dopamine signaling. These actions would therefore be able to regulate the effects of some abused drugs such as the psychostimulants.

Cocaine, loin pain, and renal vein thrombosis

We report an unusual renal complication of cocaine abuse in a young man who developed loin pain, renal vein thrombosis, and acute renal failure. Cocaine abuse should be considered in the differential diagnosis of renal vein thrombosis in young adults.

Cocaine- and amphetamine-regulated transcript (CART) peptide specific binding in pheochromocytoma cells PC12

CART (cocaine- and amphetamine-regulated transcript) peptides have been studied for ten years. We report specific binding of 125I-CART(61-102) to the rat adrenal pheochromocytoma PC12 cell line, both intact cells and cell membranes. Saturation binding to intact plated cells resulted in Kd of 0.48+/-0.16 nM and Bmax of 2228+/-529 binding sites/cell. 125I-CART(61-102) was also bound to PC12 cells differentiated using nerve growth factor to the neuronal phenotype with non-specific binding below 20%, and Kd of 1.90+/-0.27 nM and Bmax of 11,194+/-261 binding sites/cell. In competitive binding experiments, CART(61-102), CART(55-102) and di-iodinated CART(61-102) were bound to PC12 cell membranes with Ki in low nM range; their affinity to intact non-differentiated and differentiated cells was in low 10(-8) M range. In order to prove that iodination did not eliminate the pharmacological properties of CART, we tested the biological activity of di-iodinated CART(61-102). It decreased food intake in in vivo feeding experiment on fasted mice in a dose of 1 microg/mouse to the same extent as CART(61-102) in a dose of 0.5 microg/mouse.

Role of cocaine- and amphetamine-regulated transcript in estradiol-mediated neuroprotection

Estrogen reduces brain injury after experimental cerebral ischemia in part through a genomic mechanism of action. Using DNA microarrays, we analyzed the genomic response of the brain to estradiol, and we identified a transcript, cocaine- and amphetamine-regulated transcript (CART), that is highly induced in the cerebral cortex by estradiol under ischemic conditions. Using in vitro and in vivo models of neural injury, we confirmed and characterized CART mRNA and protein up-regulation by estradiol in surviving neurons, and we demonstrated that i.v. administration of a rat CART peptide is protective against ischemic brain injury in vivo. We further demonstrated binding of cAMP response element (CRE)-binding protein to a CART promoter CRE site in ischemic brain and rapid activation by CART of ERK in primary cultured cortical neurons. The findings suggest that CART is an important player in estrogen-mediated neuroprotection and a potential therapeutic agent for stroke and other neurodegenerative diseases.

Cocaine and amphetamine regulated transcript (CART) and the stress response

CART is expressed abundantly in the hypothalamic paraventricular nucleus and locus coeruleus, major corticotropin releasing factor (CRF) and noradrenaline sources, respectively. There is a bidirectional relation between CART and hypothalamo-pituitary-adrenal axis activity. CART stimulates CRF, adrenocorticotropic hormone and glucocorticoid secretion, whereas CRF and glucocorticoids increase the transcriptional activity of the CART gene; adrenalectomy declines CART expression in the hypothalamus. Stress exposure modulates CART expression in hypothalamus and amygdala in rat brain in a region and sex specific manner. CART may be a mediator peptide in the interaction between stress, drug abuse, and feeding. The review discusses the established role of CART as it relates to the stress response.