Angiotensin II mediates the axonal trafficking of tyrosine hydroxylase and dopamine β-hydroxylase mRNAs and enhances norepinephrine synthesis in primary sympathetic neurons

The role of the brain renin-angiotensin system in Parkinson´s disease

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

Conditioning electrical stimulation fails to enhance sympathetic axon regeneration

Peripheral nerve injuries are common, and there is a critical need for the development of novel therapeutics to complement surgical repair. Conditioning electrical stimulation (CES) is a novel variation to the well-studied perioperative electrical stimulation, both of which have displayed success in enhancing the regeneration of motor and sensory axons in an injured peripheral nerve. CES is a clinically attractive alternative not only because of its ability to be performed at the bedside prior to a scheduled nerve repair surgery, but it has also been shown to be superior to perioperative electrical stimulation in the enhancement of motor and sensory regeneration. However, the effects of CES on sympathetic regeneration are unknown. Therefore, we tested the effects of two clinically relevant CES paradigms on sympathetic axon regeneration and distal target reinnervation. Because of the long history of evidence for the enhancement of motor and sensory axons in response to electrical stimulation, we hypothesize that CES will also enhance sympathetic axon regeneration. Our results indicate that the growth of sympathetic axons is acutely inhibited by CES; however, at a longer survival time point post-injury, there is no difference between sham CES and the CES groups. There has been evidence to suggest that the growth of sympathetic axons is inhibited by a conditioning lesion, and that sympathetic axons may respond to electrical stimulation by sprouting rather than elongation. Our data indicate that sympathetic axons may retain some regenerative ability after CES, but no enhancement is exhibited, which may be accounted for by the inability of the current clinically relevant electrical stimulation paradigm to recruit the small-caliber sympathetic axons into activity. Further studies will be needed to optimize electrical stimulation parameters in order to enhance the regeneration of all neuron types.

Molecular mechanisms highlighting the potential role of COVID-19 in the development of neurodegenerative diseases

Coronavirus disease 2019 (COVID-19) is a contagious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In addition to the pulmonary manifestations, COVID-19 patients may present a wide range of neurological disorders as extrapulmonary presentations. In this view, several studies have recently documented the worsening of neurological symptoms within COVID-19 morbidity in patients previously diagnosed with neurodegenerative diseases (NDs). Moreover, several cases have also been reported in which the patients presented parkinsonian features after initial COVID-19 symptoms. These data raise a major concern about the possibility of communication between SARS-CoV-2 infection and the initiation and/or worsening of NDs. In this review, we have collected compelling evidence suggesting SARS-CoV-2, as an environmental factor, may be capable of developing NDs. In this respect, the possible links between SARS-CoV-2 infection and molecular pathways related to most NDs and the pathophysiological mechanisms of the NDs such as Alzheimer's disease, vascular dementia, frontotemporal dementia, Parkinson's disease, and amyotrophic lateral sclerosis will be explained.

Study on the mechanism of the Pu-erh tea (Camellia sinensis var. assamica) extract inhibiting contraction of isolated mouse duodenum

The aims of this study were to investigate the effects of three different concentrations of the Pu-erh tea extract (PTE) on the contractile activity of the isolated mouse duodenum and explore their mechanism. The contraction amplitude and frequency of the isolated mouse duodenum were inhibited by all three concentrations of PTE. The high-concentration PTE significantly (P < 0.01) inhibited the promotion effects of acetylcholine chloride or BayK8644 on the amplitude and frequency of intestinal contraction, which were comparable to those of atropine sulphate and verapamil hydrochloride, respectively. The results of UV-Vis and ELISA showed that the content of methionine-enkephalin (Met-ENK) in the PTE-treated groups was decreased to varying degrees; contrarily, the activities of tyrosine hydroxylase (TH), total nitric oxide synthase, and the content of nitric oxide were increased to different degrees. The results suggest that PTE can inhibit the contraction of the isolated mouse duodenum, and the mechanism of action is that PTE can not only inhibit the signal transduction pathways of AC-cAMP-PKA and PLC-IP3-Ca2+, but also the Ca2+ signal systems mediated by G protein-coupled M receptors through the myenteric plexus. By reducing the release of Met-ENK from the motor neurons of the myenteric plexus, the GTP-cAMP-PKK signalling pathway and the Ca2+ signalling system mediated by G protein-coupled delta receptors were inhibited. By increasing the TH activity of the motor neurons in the myenteric plexus, the norepinephrine content was increased, thereby the AC-cAMP-PKA signal transduction pathway mediated by G protein-coupled β receptors was activated. This study increases knowledge regarding the medicinal value of the Pu-erh tea.

ACE2 expression in rat brain: Implications for COVID-19 associated neurological manifestations

We examined cell type-specific expression and distribution of rat brain angiotensin-converting enzyme 2 (ACE2), the receptor for SARS-CoV-2, in the rodent brain. ACE2 is ubiquitously present in brain vasculature, with the highest density of ACE2 expressing capillaries found in the olfactory bulb, the hypothalamic paraventricular, supraoptic, and mammillary nuclei, the midbrain substantia nigra and ventral tegmental area, and the hindbrain pontine nucleus, the pre-Bötzinger complex, and nucleus of tractus solitarius. ACE2 was expressed in astrocytes and astrocytic foot processes, pericytes and endothelial cells, key components of the blood-brain barrier. We found discrete neuronal groups immunopositive for ACE2 in brainstem respiratory rhythm generating centers, including the pontine nucleus, the parafascicular/retrotrapezoid nucleus, the parabrachial nucleus, the Bötzinger, and pre-Bötzinger complexes and the nucleus of tractus solitarius; in the arousal-related pontine reticular nucleus and gigantocellular reticular nuclei; in brainstem aminergic nuclei, including substantia nigra, ventral tegmental area, dorsal raphe, and locus coeruleus; in the epithalamic habenula, hypothalamic paraventricular and supramammillary nuclei; and in the hippocampus. Identification of ACE2-expressing neurons in rat brain within well-established functional circuits facilitates prediction of possible neurological manifestations of brain ACE2 dysregulation during and after COVID-19 infection.

Structure feature and antidepressant-like activity of a novel exopolysaccharide isolated from Marasmius androsaceus fermentation broth

The structure and antidepressant like activity of MEPS2 extracted from Marasmius androsaceus subjected to submerged fermentation was systematically studied. MEPS2 is a pyranoid polysaccharide composed of glucose and arabinose, which have a molar ratio of 0.56:0.08. The molecular weight was 85,944 Da. The NMR spectrum suggested the extracted MEPS2 contained uronic acid, and the glucosyl linkage was in α form, in accordance with the analysis of FT-IR spectrum. MEPS2 can considerably enhance the levels of noradrenalin (NE) and dopamine (DA) by ELISA. In addition, western blotting results indicated that MEPS2 can enhance the expression levels of TH, D2DR, and CAMKII. Furthermore, we found that AMPT, raclopride, and prazosin blocked the immobility and time-reducing effect of MEPS2. Overall, the antidepressant-like effect of MEPS2 may be involved in catecholamine synthesis and release, and TH, D2DR and CAMKII play an important role in this process.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

SARS-CoV-2 Dissemination Through Peripheral Nerves Explains Multiple Organ Injury

Coronavirus disease (CoVID-19), caused by recently identified severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2), is characterized by inconsistent clinical presentations. While many infected individuals remain asymptomatic or show mild respiratory symptoms, others develop severe pneumonia or even respiratory distress syndrome. SARS-CoV-2 is reported to be able to infect the lungs, the intestines, blood vessels, the bile ducts, the conjunctiva, macrophages, T lymphocytes, the heart, liver, kidneys, and brain. More than a third of cases displayed neurological involvement, and many severely ill patients developed multiple organ infection and injury. However, less than 1% of patients had a detectable level of SARS-CoV-2 in the blood, raising a question of how the virus spreads throughout the body. We propose that nerve terminals in the orofacial mucosa, eyes, and olfactory neuroepithelium act as entry points for the brain invasion, allowing SARS-CoV-2 to infect the brainstem. By exploiting the subcellular membrane compartments of infected cells, a feature common to all coronaviruses, SARS-CoV-2 is capable to disseminate from the brain to periphery via vesicular axonal transport and passive diffusion through axonal endoplasmic reticula, causing multiple organ injury independently of an underlying respiratory infection. The proposed model clarifies a wide range of clinically observed phenomena in CoVID-19 patients, such as neurological symptoms unassociated with lung pathology, protracted presence of the virus in samples obtained from recovered patients, exaggerated immune response, and multiple organ failure in severe cases with variable course and dynamics of the disease. We believe that this model can provide novel insights into CoVID-19 and its long-term sequelae, and establish a framework for further research.

Tyrosine Hydroxylase Gene Polymorphisms Contribute to Opioid Dependence and Addiction by Affecting Promoter Region Function

Mounting evidence shows that drug dependence involves the complex interplay between genetics and the environment. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine (DA) synthesis, which plays an essential role in the development of drug addiction. Noradrenergic dysfunction due to abnormalities TH expression has been implicated in the pathogenesis of drug addiction. We profiled thirteen single-nucleotide polymorphisms (SNPs) and one VNTR (TCAT repeat, UniSTS:240,639) in 512 cases and 600 healthy Chinese subjects to evaluate the relationship between common variants within the TH gene and opioids dependence (OD) in the Chinese Han population. The single-marker analysis determined that rs10770141 (p < 0.001, OR 1.739, 95% CI 1.302 - 2.323) and rs10770140 (p = 0.002, OR 1.536, 95% CI 1.164 - 2.026) are risk variants for OD. The haplotype-association analyses determined that A-C-C-C was a risk factor (p = 0.006, OR 1.662, 95% CI 1.241 - 2.225) for OD. We also observed a significant association between (TACT)_9/9 and the duration of transition from the first time using opioids to the development of opioid dependence (DTFUD) (p = 0.002, OR 2.153, 95% CI 1.319 - 3.513). Taken together, this study suggests that TH gene polymorphisms may contribute to the risk of OD in the Chinese Han population.

Copper and the brain noradrenergic system

Copper (Cu) plays an essential role in the development and function of the brain. In humans, genetic disorders of Cu metabolism may cause either severe Cu deficiency (Menkes disease) or excessive Cu accumulation (Wilson disease) in the brain tissue. In either case, the loss of Cu homeostasis results in catecholamine misbalance, abnormal myelination of neurons, loss of normal brain architecture, and a spectrum of neurologic and/or psychiatric manifestations. Several metabolic processes have been identified as particularly sensitive to Cu dis-homeostasis. This review focuses on the role of Cu in noradrenergic neurons and summarizes the current knowledge of mechanisms that maintain Cu homeostasis in these cells. The impact of Cu misbalance on catecholamine metabolism and functioning of noradrenergic system is discussed.