Hypoxic-ischemic injury causes functional and structural neurovascular degeneration in the juvenile mouse retina

Optimization of an Ischemic Retinopathy Mouse Model and the Consequences of Hypoxia in a Time-Dependent Manner

The retina is one of the highest metabolically active tissues with a high oxygen consumption, so insufficient blood supply leads to visual impairment. The incidence of related conditions is increasing; however, no effective treatment without side effects is available. Furthermore, the pathomechanism of these diseases is not fully understood. Our aim was to develop an optimal ischemic retinopathy mouse model to investigate the retinal damage in a time-dependent manner. Retinal ischemia was induced by bilateral common carotid artery occlusion (BCCAO) for 10, 13, 15 or 20 min, or by right permanent unilateral common carotid artery occlusion (UCCAO). Optical coherence tomography was used to follow the changes in retinal thickness 3, 7, 14, 21 and 28 days after surgery. The number of ganglion cells was evaluated in the central and peripheral regions on whole-mount retina preparations. Expression of glial fibrillary acidic protein (GFAP) was analyzed with immunohistochemistry and Western blot. Retinal degeneration and ganglion cell loss was observed in multiple groups. Our results suggest that the 20 min BCCAO is a good model to investigate the consequences of ischemia and reperfusion in the retina in a time-dependent manner, while the UCCAO causes more severe damage in a short time, so it can be used for testing new drugs.

Sevoflurane postconditioning ameliorates cerebral hypoxia/reoxygenation injury in zebrafish involving the Akt/GSK-3β pathway activation and the microtubule-associated protein 2 promotion

Sevoflurane postconditioning has been shown to provide neuroprotection against cerebral hypoxia-ischemia injury, but the mechanisms remain elusive. Microtubule-associated protein 2 (MAP2) is implicated in early neuronal hypoxia-ischemia injury. This study aimed to investigate whether the neuroprotective effects of sevoflurane postconditioning are related to the Akt/GSK-3β pathway and its downstream target MAP2 in zebrafish hypoxia/reoxygenation (H/R) model. Sevoflurane postconditioning or GSK-3β inhibitor TDZD-8 were used to treat H/R zebrafish. The cerebral infarction, neuronal apoptosis, and mitochondrial changes were evaluated using TTC staining, TUNEL staining, and transmission electron microscopy, respectively. The distribution of MAP2 in the brain was determined by immunofluorescence imaging. The levels of Akt, p-Akt, GSK-3β, p-GSK-3β, and MAP2 proteins were evaluated by Western blotting. The neurobehavioral recovery of zebrafish was assessed based on optokinetic response behavior. Our results indicated that sevoflurane postconditioning and TDZD-8 significantly reduced the cerebral infarction area, suppressed cell apoptosis, and improved mitochondrial integrity in zebrafish subjected to H/R. Furthermore, sevoflurane postconditioning and TDZD-8 elevated the ratios of p-Akt/Akt and p-GSK-3β/GSK-3β. However, the neuroprotective effect of sevoflurane postconditioning was effectively abolished upon suppression of MAP2 expression. In conclusion, sevoflurane postconditioning ameliorated cerebral H/R injury and facilitated the restoration of neurobehavioral function through the activation of Akt/GSK-3β pathway and promotion of MAP2 expression.

The β3 adrenoceptor in proliferative retinopathies: "Cinderella" steps out of its family shadow

In the retina, hypoxic condition leads to overgrowing leaky vessels resulting in altered metabolic supply that may cause impaired visual function. Hypoxia-inducible factor-1 (HIF-1) is a central regulator of the retinal response to hypoxia by activating the transcription of numerous target genes, including vascular endothelium growth factor, which acts as a major player in retinal angiogenesis. In the present review, oxygen urge by the retina and its oxygen sensing systems including HIF-1 are discussed in respect to the role of the beta-adrenergic receptors (β-ARs) and their pharmacologic manipulation in the vascular response to hypoxia. In the β-AR family, β1- and β2-AR have long been attracting attention because their pharmacology is intensely used for human health, while β3-AR, the third and last cloned receptor is no longer increasingly emerging as an attractive target for drug discovery. Here, β3-AR, a main character in several organs including the heart, the adipose tissue and the urinary bladder, but so far a supporting actor in the retina, has been thoroughly examined in respect to its function in retinal response to hypoxia. In particular, its oxygen dependence has been taken as a key indicator of β3-AR involvement in HIF-1-mediated responses to oxygen. Hence, the possibility of β3-AR transcription by HIF-1 has been discussed from early circumstantial evidence to the recent demonstration that β3-AR acts as a novel HIF-1 target gene by playing like a putative intermediary between oxygen levels and retinal vessel proliferation. Thus, targeting β3-AR may implement the therapeutic armamentarium against neovascular pathologies of the eye.

Quantify retinal structure in high-altitude residents with and without high altitude polycythemia

BACKGROUND

To assess retinal structural parameters in high-altitude (HA) residents with and without high altitude polycythemia (HAPC) and to elucidate the relationship between retinal structural parameters and hemoglobin (HGB).

METHODS

This cross-sectional study included 55 HAPC patients and 52 healthy HA residents. Retinal structural parameters included retinal nerve fiber layer (RNFL) thickness, optic nerve head (ONH) parameters and retinal vessel diameter. RNFL thickness were acquired from spectral domain optical coherence tomography (SD-OCT) built-in software. ONH parameters including neuroretina rim height, cup area, disc area and vertical cup/disc ratio were obtained by OCT built-in software and ImageJ software. Retinal vessel measurements including central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE) and AVR (artery/vein ratio) were calculated by revised formulas for summarizing retinal vessel diameters. All parameters were compared between HAPC group versus healthy HA group. The associations between retinal parameters and HGB were assessed by Pearson correlation analyses.

RESULTS

In comparison of HAPC group versus healthy HA group, RNFL thickness was thicker in the nasal quadrant of the optic disc in HAPC group (74.82 ± 14.4 VS. 66.06 ± 13.71 μm, P = 0.002). Bigger disc area and bigger cup area were also observed in HAPC group (all P < 0.05). Meanwhile, the value of CRVE was higher in HAPC group which suggested that retinal veins dilated significantly in HAPC patients (P < 0.001), however, CRAE and AVR were comparable between groups. Pearson analyses revealed that HGB was positive correlated with CRVE in HAPC group (r = 0.469, P = 0.003).

CONCLUSIONS

long-term HA exposure secondary HAPC could result in thickened RNFL, enlarged ONH and dilated retinal veins. Moreover, increased blood viscosity caused by HGB should be responsible for dilated veins, but not for thickened RNFL and enlarged ONH. This study deepens the understanding of the impact of HA environment on retina.

The Assessment of Endovascular Therapies in Ischemic Stroke: Management, Problems and Future Approaches

Ischemic stroke accounts for over 80% of all strokes and is one of the leading causes of mortality and permanent disability worldwide. Intravenous administration of recombinant tissue plasminogen activator (rt-PA) is an approved treatment strategy for acute ischemic stroke of large arteries within 4.5 h of onset, and mechanical thrombectomy can be used for large arteries occlusion up to 24 h after onset. Improving diagnostic work up for acute treatment, reducing onset-to-needle time and urgent radiological access angiographic CT images (angioCT) and Magnetic Resonance Imaging (MRI) are real problems for many healthcare systems, which limits the number of patients with good prognosis in real world compared to the results of randomized controlled trials. The applied endovascular procedures demonstrated high efficacy, but some cellular mechanisms, following reperfusion, are still unknown. Changes in the morphology and function of mitochondria associated with reperfusion and ischemia-reperfusion neuronal death are still understudied research fields. Moreover, future research is needed to elucidate the relationship between continuously refined imaging techniques and the variable structure or physical properties of the clot along with vascular permeability and the pleiotropism of ischemic reperfusion lesions in the penumbra, in order to define targeted preventive procedures promoting long-term health benefits.