AT1 -R is involved in the development of long-lasting, region-dependent and oxidative stress-independent astrocyte morphological alterations induced by Ketamine

The angiotensin II receptors type 1 and 2 modulate astrocytes and their crosstalk with microglia and neurons in an in vitro model of ischemic stroke

BACKGROUND

Astrocytes are the most abundant cell type of the central nervous system and are fundamentally involved in homeostasis, neuroprotection, and synaptic plasticity. This regulatory function of astrocytes on their neighboring cells in the healthy brain is subject of current research. In the ischemic brain we assume disease specific differences in astrocytic acting. The renin-angiotensin-aldosterone system regulates arterial blood pressure through endothelial cells and perivascular musculature. Moreover, astrocytes express angiotensin II type 1 and 2 receptors. However, their role in astrocytic function has not yet been fully elucidated. We hypothesized that the angiotensin II receptors impact astrocyte function as revealed in an in vitro system mimicking cerebral ischemia. Astrocytes derived from neonatal wistar rats were exposed to telmisartan (angiotensin II type 1 receptor-blocker) or PD123319 (angiotensin II type 2 receptor-blocker) under normal conditions (control) or deprivation from oxygen and glucose. Conditioned medium (CM) of astrocytes was harvested to elucidate astrocyte-mediated indirect effects on microglia and cortical neurons.

RESULT

The blockade of angiotensin II type 1 receptor by telmisartan increased the survival of astrocytes during ischemic conditions in vitro without affecting their proliferation rate or disturbing their expression of S100A10, a marker of activation. The inhibition of the angiotensin II type 2 receptor pathway by PD123319 resulted in both increased expression of S100A10 and proliferation rate. The CM of telmisartan-treated astrocytes reduced the expression of pro-inflammatory mediators with simultaneous increase of anti-inflammatory markers in microglia. Increased neuronal activity was observed after treatment of neurons with CM of telmisartan- as well as PD123319-stimulated astrocytes.

CONCLUSION

Data show that angiotensin II receptors have functional relevance for astrocytes that differs in healthy and ischemic conditions and effects surrounding microglia and neuronal activity via secretory signals. Above that, this work emphasizes the strong interference of the different cells in the CNS and that targeting astrocytes might serve as a therapeutic strategy to influence the acting of glia-neuronal network in de- and regenerative context.

Selective disruption of mTORC1 and mTORC2 in VTA astrocytes induces depression and anxiety-like behaviors in mice

Dysfunction of the mechanistic target of rapamycin (mTOR) signaling pathway is implicated in neuropsychiatric disorders including depression and anxiety. Most studies have been focusing on neurons, and the function of mTOR signaling pathway in astrocytes is less investigated. mTOR forms two distinct complexes, mTORC1 and mTORC2, with key scaffolding protein Raptor and Rictor, respectively. The ventral tegmental area (VTA), a vital component of the brain reward system, is enrolled in regulating both depression and anxiety. In the present study, we aimed to examine the regulation effect of VTA astrocytic mTOR signaling pathway on depression and anxiety. We specifically deleted Raptor or Rictor in VTA astrocytes in mice and performed a series of behavioral tests for depression and anxiety. Deletion of Raptor and Rictor both decreased the immobility time in the tail suspension test and the latency to eat in the novelty suppressed feeding test, and increased the horizontal activity and the movement time in locomotor activity. Deletion of Rictor decreased the number of total arm entries in the elevated plus-maze test and the vertical activity in locomotor activity. These data suggest that VTA astrocytic mTORC1 plays a role in regulating depression-related behaviors and mTORC2 is involved in both depression and anxiety-related behaviors. Our results indicate that VTA astrocytic mTOR signaling pathway might be new targets for the treatment of psychiatric disorders.

Differential Susceptibility to Propofol and Ketamine in Primary Cultures of Young and Senesced Astrocytes

The adverse effects of general anesthesia on the long-term cognition of young children and senior adults have become of concern in recent years. Previously, mechanistic and pathogenic investigations focused on neurons, and little is known about the effect of commonly used intravenous anesthetics such as propofol and ketamine on astrocytes. Recently, astrocyte dysfunction has been implicated in a wide range of age-related brain diseases. In this study, we examined the survival and viability of both young and senescent astrocytes in culture after adding propofol and ketamine to the media at varying strengths. Oxidative stimulus was applied to commercially available fetal cell lines of human astrocytes in vitro to induce morphological changes in cellular senescence. Our results indicate that propofol reduces the survival of young astrocytes as compared to controls, as well as to ketamine. These effects were seen in comparisons of total cell count and at both high and low dose concentrations. High doses of propofol also significantly reduced cell viability compared to those exposed to baseline controls and ketamine. Senescent astrocytes, on the other hand, demonstrated cell count reductions as compared to baseline controls and ketamine when exposed to either DMSO or propofol. The data show differential susceptibility of young astrocytes to propofol than to ketamine. The observed cell count reduction may be related to the adverse effects of propofol on mitochondrial function and free radical production, as described in previous studies. We speculate that ketamine may have a more favorable safety profile in infants and young children.

Lipoxin A4 methyl ester attenuated ketamine-induced neurotoxicity in SH-SY5Y cells via regulating leptin pathway

Ketamine, the widely used intravenous anesthetic, has been reported to cause neurotoxicity and disturbs normal neurogenesis. However, the efficacy of current treatment strategies targeting ketamine's neurotoxicity remains limited. Lipoxin A4 methyl ester (LXA4 ME) is relatively stable lipoxin analog, which serves an important role in protecting against early brain injury. The purpose of this study was to investigate the protective effect of LXA4 ME on ketamine-caused cytotoxicity in SH-SY5Y cells, as well as the underlying mechanisms. Cell viability, apoptosis and endoplasmic reticulum stress (ER stress) were detected by adopting experimental techniques including CCK-8 assay, flow cytometry, western blotting and transmission electron microscope. Furthermore, examining the expression of leptin and its receptor (LepRb), we also measured the levels of activation of the leptin signaling pathway. Our results showed that LXA4 ME intervention promoted the cell viability, inhibited cell apoptosis, and reduced the expression of ER stress related protein and morphological changes induced by ketamine. In addition, inhibition of leptin signaling pathway caused by ketamine could be reversed by LXA4 ME. However, as the specific inhibitor of leptin pathway, leptin antagonist triple mutant human recombinant (leptin tA) attenuated the cytoprotective effect of LXA4 ME against ketamine-induced neurotoxicity. In conclusion, our findings demonstrated LXA4 ME could exert a neuroprotective effect on ketamine-induced neuronal injury via activation of the leptin signaling pathway.

Early IGF-1 Gene Therapy Prevented Oxidative Stress and Cognitive Deficits Induced by Traumatic Brain Injury

Traumatic Brain Injury (TBI) remains a leading cause of morbidity and mortality in adults under 40 years old. Once primary injury occurs after TBI, neuroinflammation and oxidative stress (OS) are triggered, contributing to the development of many TBI-induced neurological deficits, and reducing the probability of critical trauma patients´ survival. Regardless the research investment on the development of anti-inflammatory and neuroprotective treatments, most pre-clinical studies have failed to report significant effects, probably because of the limited blood brain barrier permeability of no-steroidal or steroidal anti-inflammatory drugs. Lately, neurotrophic factors, such as the insulin-like growth factor 1 (IGF-1), are considered attractive therapeutic alternatives for diverse neurological pathologies, as they are neuromodulators linked to neuroprotection and anti-inflammatory effects. Considering this background, the aim of the present investigation is to test early IGF-1 gene therapy in both OS markers and cognitive deficits induced by TBI. Male Wistar rats were injected via Cisterna Magna with recombinant adenoviral vectors containing the IGF-1 gene cDNA 15 min post-TBI. Animals were sacrificed after 60 min, 24 h or 7 days to study the advanced oxidation protein products (AOPP) and malondialdehyde (MDA) levels, to recognize the protein oxidation damage and lipid peroxidation respectively, in the TBI neighboring brain areas. Cognitive deficits were assessed by evaluating working memory 7 days after TBI. The results reported significant increases of AOPP and MDA levels at 60 min, 24 h, and 7 days after TBI in the prefrontal cortex, motor cortex and hippocampus. In addition, at day 7, TBI also reduced working memory performance. Interestingly, AOPP, and MDA levels in the studied brain areas were significantly reduced after IGF-1 gene therapy that in turn prevented cognitive deficits, restoring TBI-animals working memory performance to similar values regarding control. In conclusion, early IGF-1 gene therapy could be considered a novel therapeutic approach to targeting neuroinflammation as well as to preventing some behavioral deficits related to TBI.

Amphetamine Induces Oxidative Stress, Glial Activation and Transient Angiogenesis in Prefrontal Cortex via AT1-R

Background: Amphetamine (AMPH) alters neurons, glia and microvessels, which affects neurovascular unit coupling, leading to disruption in brain functions such as attention and working memory. Oxidative stress plays a crucial role in these alterations. The angiotensin type I receptors (AT₁-R) mediate deleterious effects, such as oxidative/inflammatory responses, endothelial dysfunction, neuronal oxidative damage, alterations that overlap with those observed from AMPH exposure. Aims: The aim of this study was to evaluate the AT₁-R role in AMPH-induced oxidative stress and glial and vascular alterations in the prefrontal cortex (PFC). Furthermore, we aimed to evaluate the involvement of AT₁-R in the AMPH-induced short-term memory and working memory deficit. Methods: Male Wistar rats were repeatedly administered with the AT₁-R blocker candesartan (CAND) and AMPH. Acute oxidative stress in the PFC was evaluated immediately after the last AMPH administration by determining lipid and protein peroxidation. After 21 off-drug days, long-lasting alterations in the glia, microvessel architecture and to cognitive tasks were evaluated by GFAP, CD11b and von Willebrand immunostaining and by short-term and working memory assessment. Results: AMPH induced acute oxidative stress, long-lasting glial reactivity in the PFC and a working memory deficit that were prevented by AT₁-R blockade pretreatment. Moreover, AMPH induces transient angiogenesis in PFC via AT₁-R. AMPH did not affect short-term memory. Conclusion: Our results support the protective role of AT₁-R blockade in AMPH-induced oxidative stress, transient angiogenesis and long-lasting glial activation, preserving working memory performance.

Insights into the actions of angiotensin-1 receptor (AT1R) inverse agonists: Perspectives and implications in COVID-19 treatment

New coronavirus SARS-CoV-2 (COVID-19) has caused chaos in health care systems. Clinical manifestations of COVID-19 are variable, with a complex pathophysiology and as yet no specific treatment. It has been suggested that the renin-angiotensin-aldosterone system has a possible role in the severity of cases and the number of deaths. Our hypothesis is that drugs with inverse agonist effects to the angiotensin-1 receptor can be promising tools in the management of patients with COVID-19, possibly avoiding complications and the poor evolution in some cases. Any risk factors first need to be identified, and the most appropriate time to administer the drugs during the course of the infection also needs to be established. Several angiotensin receptor blockers (ARB) have a favorable profile and are important candidates for the treatment of COVID-19. In this review we discussed a set of compounds with favorable profile for COVID-19 treatment, including azilsartan, candesartan, eprosartan, EXP3174, olmesartan, telmisartan, and valsartan. They are effective as inverse agonists and could reduce the "cytokine storm" and reducing oxidative stress. As COVID-19 disease has several evolution patterns, the effectiveness of ARB therapy would be related to infection "timing", patient risk factors, previous use of ARBs, and the specific molecular effects of an ARB. However, controlled studies are needed to identify whether ARBs are beneficial in the treatment of patients with COVID-19.