Role of myeloid cells in ischemic retinopathies: recent advances and unanswered questions

Myeloid cells including microglia and macrophages play crucial roles in retinal homeostasis by clearing cellular debris and regulating inflammation. These cells are activated in several blinding ischemic retinal diseases including diabetic retinopathy, where they may exert both beneficial and detrimental effects on neurovascular function and angiogenesis. Myeloid cells impact the progression of retinal pathologies and recent studies suggest that targeting myeloid cells is a promising therapeutic strategy to mitigate diabetic retinopathy and other ischemic retinal diseases. This review summarizes the recent advances in our understanding of the role of microglia and macrophages in retinal diseases and focuses on the effects of myeloid cells on neurovascular injury and angiogenesis in ischemic retinopathies. We highlight gaps in knowledge and advocate for a more detailed understanding of the role of myeloid cells in retinal ischemic injury to fully unlock the potential of targeting myeloid cells as a therapeutic strategy for retinal ischemia.

Calbindin 2-specific deletion of arginase 2 preserves visual function after optic nerve crush

We previously found that global deletion of the mitochondrial enzyme arginase 2 (A2) limits optic nerve crush (ONC)-induced neuronal death. Herein, we examined the cell-specific role of A2 in this pathology by studies using wild type (WT), neuronal-specific calbindin 2 A2 KO (Calb2cre/+ A2 f/f), myeloid-specific A2 KO (LysMcre/+ A2f/f), endothelial-specific A2 KO (Cdh5cre/+ A2f/f), and floxed controls. We also examined the impact of A2 overexpression on mitochondrial function in retinal neuronal R28 cells. Immunolabeling showed increased A2 expression in ganglion cell layer (GCL) neurons of WT mice within 6 h-post injury and inner retinal neurons after 7 days. Calb2 A2 KO mice showed improved neuronal survival, decreased TUNEL-positive neurons, and improved retinal function compared to floxed littermates. Neuronal loss was unchanged by A2 deletion in myeloid or endothelial cells. We also found increased expression of neurotrophins (BDNF, FGF2) and improved survival signaling (pAKT, pERK1/2) in Calb2 A2 KO retinas within 24-hour post-ONC along with suppression of inflammatory mediators (IL1β, TNFα, IL6, and iNOS) and apoptotic markers (cleavage of caspase3 and PARP). ONC increased GFAP and Iba1 immunostaining in floxed controls, and Calb2 A2 KO dampened this effect. Overexpression of A2 in R28 cells increased Drp1 expression, and decreased mitochondrial respiration, whereas ABH-induced inhibition of A2 decreased Drp1 expression and improved mitochondrial respiration. Finally, A2 overexpression or excitotoxic treatment with glutamate significantly impaired mitochondrial function in R28 cells as shown by significant reductions in basal respiration, maximal respiration, and ATP production. Further, glutamate treatment of A2 overexpressing cells did not induce further deterioration in their mitochondrial function, indicating that A2 overexpression or glutamate insult induce comparable alterations in mitochondrial function. Our data indicate that neuronal A2 expression is neurotoxic after injury, and A2 deletion in Calb2 expressing neurons limits ONC-induced retinal neurodegeneration and improves visual function.

The arginase 1/ornithine decarboxylase pathway suppresses HDAC3 to ameliorate the myeloid cell inflammatory response: implications for retinal ischemic injury

The enzyme arginase 1 (A1) hydrolyzes the amino acid arginine to form L-ornithine and urea. Ornithine is further converted to polyamines by the ornithine decarboxylase (ODC) enzyme. We previously reported that deletion of myeloid A1 in mice exacerbates retinal damage after ischemia/reperfusion (IR) injury. Furthermore, treatment with A1 protects against retinal IR injury in wild-type mice. PEG-A1 also mitigates the exaggerated inflammatory response of A1 knockout (KO) macrophages in vitro. Here, we sought to identify the anti-inflammatory pathway that confers macrophage A1-mediated protection against retinal IR injury. Acute elevation of intraocular pressure was used to induce retinal IR injury in mice. A multiplex cytokine assay revealed a marked increase in the inflammatory cytokines interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the retina at day 5 after IR injury. In vitro, blocking the A1/ODC pathway augmented IL-1β and TNF-α production in stimulated macrophages. Furthermore, A1 treatment attenuated the stimulated macrophage metabolic switch to a pro-inflammatory glycolytic phenotype, whereas A1 deletion had the opposite effect. Screening for histone deacetylases (HDACs) which play a role in macrophage inflammatory response showed that A1 deletion or ODC inhibition increased the expression of HDAC3. We further showed the involvement of HDAC3 in the upregulation of TNF-α but not IL-1β in stimulated macrophages deficient in the A1/ODC pathway. Investigating HDAC3 KO macrophages showed a reduced inflammatory response and a less glycolytic phenotype upon stimulation. In vivo, HDAC3 co-localized with microglia/macrophages at day 2 after IR in WT retinas and was further increased in A1-deficient retinas. Collectively, our data provide initial evidence that A1 exerts its anti-inflammatory effect in macrophages via ODC-mediated suppression of HDAC3 and IL-1β. Collectively we propose that interventions that augment the A1/ODC pathway and inhibit HDAC3 may confer therapeutic benefits for the treatment of retinal ischemic diseases.

Multi-color Flow Cytometry Protocol to Characterize Myeloid Cells in Mouse Retina Research

Myeloid cells, specifically microglia and macrophages, are activated in retinal diseases and can improve or worsen retinopathy outcomes based on their inflammatory phenotype. However, assessing the myeloid cell response after retinal injury in mice remains challenging due to the small tissue size and the challenges of distinguishing microglia from infiltrating macrophages. In this protocol paper, we describe a flow cytometry-based protocol to assess retinal microglia/macrophage and their inflammatory phenotype after injury. The protocol is amenable to the incorporation of other markers of interest to other researchers. Key features This protocol describes a flow cytometry-based method to analyze the myeloid cell response in retinopathy mouse models. The protocol can distinguish between microglia- and monocyte-derived macrophages. It can be modified to incorporate markers of interest. We show representative results from three different retinopathy models, namely ischemia-reperfusion injury, endotoxin-induced uveitis, and oxygen-induced retinopathy.

Contralesional angiotensin type 2 receptor activation contributes to recovery in experimental stroke

We and others have previously shown that angiotensin II receptor type 2 receptor (AT2R) is upregulated in the contralesional hemisphere after stroke in normoglycemic Wistar rats. In this study, we examined the expression of AT2R in type 2 diabetic Goto-Kakizaki (GK) rats and control Wistars after stroke. We also tested the contribution of the contralesional AT2R in recovery after stroke through a specific knockdown of the AT2R in this hemisphere only. Two experiments were conducted. In the first experiment, GK rats were subjected to middle cerebral artery occlusion (MCAO) and treated with the angiotensin II receptor type 1 receptor (AT1R) blocker candesartan or saline at reperfusion. Stroke outcomes, as well as AT2R expression, were examined and compared to control Wistars at 24 h. In the second experiment, localized AT2R knockdown was achieved through intrastriatal injection of short hairpin RNA (shRNA) lentiviral particles or non-targeting control into the left-brain hemisphere of Wistar rats. After 14 days, rats were subjected to right MCAO and treated with the AT2R agonist, Compound 21 (C21), or saline for 7 days. Behavioral outcomes were assessed for up to 10 days. In the first experiment, stroke reduced the expression of AT2R in GK rats. Candesartan treatment failed to improve the neurobehavioral outcomes, preserve vascular integrity or reduce oxidative/nitrative stress or apoptotic markers at 24 h post stroke in these animals. In the second experiment, contralesional AT2R knockdown reduced the C21-mediated functional recovery after stroke. In conclusion, contralesional AT2R upregulation after stroke is blunted in diabetic rats which show reduced sensitivity to post-stroke candesartan treatment. Contralesional AT2R could be involved in C21-mediated functional recovery after stroke.

Targeting proliferative retinopathy: Arginase 1 limits vitreoretinal neovascularization and promotes angiogenic repair

Current therapies for treatment of proliferative retinopathy focus on retinal neovascularization (RNV) during advanced disease and can trigger adverse side-effects. Here, we have tested a new strategy for limiting neurovascular injury and promoting repair during early-stage disease. We have recently shown that treatment with a stable, pegylated drug form of the ureohydrolase enzyme arginase 1 (A1) provides neuroprotection in acute models of ischemia/reperfusion injury, optic nerve crush, and ischemic stroke. Now, we have determined the effects of this treatment on RNV, vascular repair, and retinal function in the mouse oxygen-induced retinopathy (OIR) model of retinopathy of prematurity (ROP). Our studies in the OIR model show that treatment with pegylated A1 (PEG-A1), inhibits pathological RNV, promotes angiogenic repair, and improves retinal function by a mechanism involving decreased expression of TNF, iNOS, and VEGF and increased expression of FGF2 and A1. We further show that A1 is expressed in myeloid cells and areas of RNV in retinal sections from mice with OIR and human diabetic retinopathy (DR) patients and in blood samples from ROP patients. Moreover, studies using knockout mice with hemizygous deletion of A1 show worsened RNV and retinal injury, supporting the protective role of A1 in limiting the OIR-induced pathology. Collectively, A1 is critically involved in reparative angiogenesis and neuroprotection in OIR. Pegylated A1 may offer a novel therapy for limiting retinal injury and promoting repair during proliferative retinopathy.

Investigation of Retinal Metabolic Function in Type 1 Diabetic Akita Mice

Diabetic retinopathy (DR) is the leading cause of vision loss in working age adults. Understanding the retinal metabolic response to circulating high glucose levels in diabetic patients is critical for development of new therapeutics to treat DR. Measuring retinal metabolic function using the Seahorse analyzer is a promising technique to investigate the effect of hyperglycemia on retinal glycolysis and mitochondrial respiration. Here, we analyzed the retinal metabolic function in young and old diabetic and control mice. We also compared the expression of key glycolytic enzymes between the two groups. The Seahorse XF analyzer was used to measure the metabolic function of retina explants from young and old type 1 diabetic Akita (Ins2^Akita) mice and their control littermates. Rate-limiting glycolytic enzymes were analyzed in retina lysates from the two age groups by Western blotting. Retinas from young adult Akita mice showed a decreased glycolytic response as compared to control littermates. However, this was not observed in the older mice. Western blotting analysis showed decreased expression of the glycolytic enzyme PFKFB3 in the young Akita mice retinas. Measurement of the oxygen consumption rate showed no difference in retinal mitochondrial respiration between Akita and WT littermates under normal glucose conditions ex vivo despite mitochondrial fragmentation in the Akita retinas as examined by electron microscopy. However, Akita mice retinas showed decreased mitochondrial respiration under glucose-free conditions. In conclusion, diabetic retinas display a decreased glycolytic response during the early course of diabetes which is accompanied by a reduction in PFKFB3. Diabetic retinas exhibit decreased mitochondrial respiration under glucose deprivation.

Preclinical investigation of Pegylated arginase 1 as a treatment for retina and brain injury

Arginase 1 (A1) is the enzyme that hydrolyzes the amino acid, L-arginine, to ornithine and urea. We have previously shown that A1 deletion worsens retinal ischemic injury, suggesting a protective role of A1. In this translational study, we aimed to study the utility of systemic pegylated A1 (PEG-A1, recombinant human arginase linked to polyethylene glycol) treatment in mouse models of acute retinal and brain injury. Cohorts of WT mice were subjected to retinal ischemia-reperfusion (IR) injury, traumatic optic neuropathy (TON) or brain cerebral ischemia via middle cerebral artery occlusion (MCAO) and treated with intraperitoneal injections of PEG-A1 or vehicle (PEG only). Drug penetration into retina and brain tissues was measured by western blotting and immunolabeling for PEG. Neuroprotection was measured in a blinded fashion by quantitation of NeuN (neuronal marker) immunolabeling of retina flat-mounts and brain infarct area using triphenyl tetrazolium chloride (TTC) staining. Furthermore, ex vivo retina explants and in vitro retina neuron cultures were subjected to oxygen-glucose deprivation (OGD) followed by reoxygenation (R) and treated with PEG-A1. PEG-A1 given systemically did not cross the intact blood-retina/brain barriers in sham controls but reached the retina and brain after injury. PEG-A1 provided neuroprotection after retinal IR injury, TON and cerebral ischemia. PEG-A1 treatment was also neuroprotective in retina explants subjected to OGD/R but did not improve survival in retinal neuronal cultures exposed to OGD/R. In summary, systemic PEG-A1 administration is neuroprotective and provides an excellent route to deliver the drug to the retina and the brain after acute injury.

Endothelial arginase 2 mediates retinal ischemia/reperfusion injury by inducing mitochondrial dysfunction

Objective

Retinal ischemic disease is a major cause of vision loss. Current treatment options are limited to late-stage diseases, and the molecular mechanisms of the initial insult are not fully understood. We have previously shown that the deletion of the mitochondrial arginase isoform, arginase 2 (A2), limits neurovascular injury in models of ischemic retinopathy. Here, we investigated the involvement of A2-mediated alterations in mitochondrial dynamics and function in the pathology.

Methods

We used wild-type (WT), global A2 knockout (A2KO-) mice, cell-specific A2 knockout mice subjected to retinal ischemia/reperfusion (I/R), and bovine retinal endothelial cells (BRECs) subjected to an oxygen-glucose deprivation/reperfusion (OGD/R) insult. We used western blotting to measure levels of cell stress and death markers and the mitochondrial fragmentation protein, dynamin related protein 1 (Drp1). We also used live cell mitochondrial labeling and Seahorse XF analysis to evaluate mitochondrial fragmentation and function, respectively.

Results

We found that the global deletion of A2 limited the I/R-induced disruption of retinal layers, fundus abnormalities, and albumin extravasation. The specific deletion of A2 in endothelial cells was protective against I/R-induced neurodegeneration. The OGD/R insult in BRECs increased A2 expression and induced cell stress and cell death, along with decreased mitochondrial respiration, increased Drp1 expression, and mitochondrial fragmentation. The overexpression of A2 in BREC also decreased mitochondrial respiration, promoted increases in the expression of Drp1, mitochondrial fragmentation, and cell stress and resulted in decreased cell survival. In contrast, the overexpression of the cytosolic isoform, arginase 1 (A1), did not affect these parameters.

Conclusions

This study is the first to show that A2 in endothelial cells mediates retinal ischemic injury through a mechanism involving alterations in mitochondrial dynamics and function.

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Ischemic retinopathy is a common feature of blinding eye disease.

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Arginase 2 overexpression in endothelial cells induces mitochondrial dysfunction.

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Endothelial-specific arginase 2 deletion improves neuronal survival after ischemia.

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Endothelial cell arginase 2 plays a crucial role in ischemic retinal injury.

Arginase Pathway in Acute Retina and Brain Injury: Therapeutic Opportunities and Unexplored Avenues

Ischemic retinopathies represent a major cause of visual impairment and blindness. They include diabetic retinopathy (DR), acute glaucoma, retinopathy of prematurity (ROP), and central (or branch) retinal artery occlusion (CRAO). These conditions share in common a period of ischemia or reduced blood supply to the retinal tissue that eventually leads to neuronal degeneration. Similarly, acute brain injury from ischemia or trauma leads to neurodegeneration and can have devastating consequences in patients with stroke or traumatic brain injury (TBI). In all of these conditions, current treatment strategies are limited by their lack of effectiveness, adverse effects or short time window for administration. Therefore, there is a great need to identify new therapies for acute central nervous system (CNS) injury. In this brief review article, we focus on the pathway of the arginase enzyme as a novel therapeutic target for acute CNS injury. We review the recent work on the role of arginase enzyme and its downstream components in neuroprotection in both retina and brain acute injury models. Delineating the similarities and differences between the role of arginase in the retina and brain neurodegeneration will allow for better understanding of the role of arginase in CNS disorders. This will also facilitate repurposing the arginase pathway as a new therapeutic target in both retina and brain diseases.

Utility of LysM-cre and Cdh5-cre Driver Mice in Retinal and Brain Research: An Imaging Study Using tdTomato Reporter Mouse

Purpose

The lysozyme 2 (Lyz2 or LysM) cre mouse is extensively used to achieve genetic manipulation in myeloid cells and it has been widely employed in retinal research. However, LysM has been recently described to be expressed in brain neurons and there is a debate on whether it is also expressed by resident microglia in addition to infiltrating macrophages.

Methods

We examined LysM-cre recombination in retinal tissue using a LysM-cre/tdTomato reporter mouse together with immunolabeling for several retinal cell markers. We further compared LysM-cre tdTomato recombination with that of Cdh5-cre driver, which is expressed in both endothelial and hematopoietic cells.

Results

LysM-cre was strongly expressed in most microglia/resident macrophages in neonatal retinas (P8) and to a lesser extent in microglia of adult retinas. In addition, there was some neuronal recombination (8 %) of LysM-cre specifically in adult retinal ganglion cells and amacrine cells. After retinal ischemia-reperfusion injury, LysM-cre was strongly expressed in microglia/infiltrating macrophages. Cdh5-cre was expressed in endothelial and myeloid cells of P8 pups retinas. Unexpectedly, Cdh5 showed additional expression in adult mouse retinal ganglion cells and brain neurons.

Conclusions

LysM-cre is expressed in macrophages and a subset of microglia together with a small but significant recombination of LysM-cre in the retinal neurons of adult mice. Cdh5 also showed some neuronal expression in both retina and brain of adult mice. These findings should be taken into consideration when interpreting results from central nervous system research using LysM-cre and Cdh5-cre mice.

Dose-response, therapeutic time-window and tPA-combinatorial efficacy of compound 21: A randomized, blinded preclinical trial in a rat model of thromboembolic stroke

The aim of this translational, randomized, controlled, blinded preclinical trial was to determine the effect of compound 21 (C21) in embolic stroke. Rats were subjected to embolic-middle cerebral artery occlusion (eMCAO). They received C21 (0.01, 0.03 and 0.06 mg/kg/d) or saline (orally) for five days, with the first-dose given IV at 3 h post-eMCAO. For the time-window study, the optimal-dose of C21 was initiated at 3, 6 or 24 h post-eMCAO and continued for five days. For the combinatorial study, animals received IV-tissue plasminogen activator (tPA) at either 2 or 4 h, with IV-C21 (0.01 mg/kg) or saline at 3 h post-eMCAO and daily thereafter for five days. After performing the behavior tests, brains were collected for analyses. The dose-response study showed significant motor improvements with the lowest-dose (0.01 mg/kg) of C21. In the time-window study, this same dose resulted in improvements when given 6 h and 24 h post-eMCAO. Moreover, C21-treated animals performed better on the novel object recognition test. Neither the single treatment with C21 or tPA (4 h) nor the combination therapy was effective in reducing the hemorrhage or infarct size, although C21 alone lowered sensorimotor deficit scores post-eMCAO. Future studies should focus on the long-term cognitive benefits of C21, rather than acute neuroprotection.

Deletion of Arginase 2 Ameliorates Retinal Neurodegeneration in a Mouse Model of Multiple Sclerosis

Optic neuritis is a major clinical feature of multiple sclerosis (MS) and can lead to temporary or permanent vision loss. Previous studies from our laboratory have demonstrated the critical involvement of arginase 2 (A2) in retinal neurodegeneration in models of ischemic retinopathy. The current study was undertaken to investigate the role of A2 in MS-mediated retinal neuronal damage and degeneration. Experimental autoimmune encephalomyelitis (EAE) was induced in wild-type (WT) and A2 knockout (A2^-/-) mice. EAE-induced motor deficits, loss of retinal ganglion cells, retinal thinning, inflammatory signaling, and glial activation were studied in EAE-treated WT and A2^-/- mice and their respective controls. Increased expression of A2 was observed in WT retinas in response to EAE induction. EAE-induced motor deficits were markedly reduced in A2^-/- mice compared with WT controls. Retinal flat mount studies demonstrated a significant reduction in the number of RGCs in WT EAE retinas in comparison with normal control mice. A significant improvement in neuronal survival was evident in retinas of EAE-induced A2^-/- mice compared with WT. RNA levels of the proinflammatory molecules CCL2, COX2, IL-1α, and IL-12α were significantly reduced in the A2^-/- EAE retinas compared with WT EAE. EAE-induced activation of glia (microglia and Müller cells) was markedly reduced in A2^-/- retinas compared with WT. Western blot analyses showed increased levels of phospho-ERK1/2 and reduced levels of phospho-BAD in the WT EAE retina, while these changes were prevented in A2^-/- mice. In conclusion, our studies establish EAE as an excellent model to study MS-mediated retinal neuronal damage and suggest the potential value of targeting A2 as a therapy to prevent MS-mediated retinal neuronal injury.

Angiotensin II type 2 receptor stimulation with compound 21 improves neurological function after stroke in female rats: a pilot study

The angiotensin II type 2 receptor (AT2R) agonist, compound 21 (C21), has been shown to be neurovascularly protective after ischemic stroke in male rats. In the current study, we aim to study the impact of C21 treatment on female rats. Young female Wistar rats were subjected to different durations of middle cerebral artery occlusion (MCAO) (3 h, 2 h, and 1 h) using a silicone-coated monofilament, treated at reperfusion with 0.03 mg/kg ip of C21 and followed up for different times (1, 3, and 14 days) after stroke. Behavioral tests were performed (Bederson, paw grasp, beam walk, and rotarod), and animals were euthanized for infarct size analysis and Western blot analysis. In vitro, primary male and female brain microvascular endothelial cells (ECs) were grown in culture, and the expression of the AT2R was compared between males and females. At 1 day, C21 treatment resulted in an improvement in Bederson scores. However, at 3 days and 14 days, the impact of C21 on stroke outcomes was less robust. In vitro, the expression of the AT2R was significantly higher in female ECs compared with male ECs. In conclusion, C21 improves Bederson scores after stroke in female rats when administered early at reperfusion. The ability of C21 to exert its neuroprotective effects might be affected by fluctuating levels of female hormones. NEW & NOTEWORTHY The present study shows the neuroprotective impact of C21 on ischemic stroke in female rats and how the protective effects of C21 can be influenced by the hormonal status of female rodents.

Brain Vasculature and Cognition

There is a complex interaction between the brain and the cerebral vasculature to meet the metabolic demands of the brain for proper function. Preservation of cerebrovascular function and integrity has a central role in this sophisticated communication within the brain, and any derangements can have deleterious acute and chronic consequences. In almost all forms of cognitive impairment, from mild to Alzheimer disease, there are changes in cerebrovascular function and structure leading to decreased cerebral blood flow, which may initiate or worsen cognitive impairment. In this focused review, we discuss the contribution of 2 major vasoactive pathways to cerebrovascular dysfunction and cognitive impairment in an effort to identify early intervention strategies.

Targeting Polyamine Oxidase to Prevent Excitotoxicity-Induced Retinal Neurodegeneration

Dysfunction of retinal neurons is a major cause of vision impairment in blinding diseases that affect children and adults worldwide. Cellular damage resulting from polyamine catabolism has been demonstrated to be a major player in many neurodegenerative conditions. We have previously shown that inhibition of polyamine oxidase (PAO) using MDL 72527 significantly reduced retinal neurodegeneration and cell death signaling pathways in hyperoxia-mediated retinopathy. In the present study, we investigated the impact of PAO inhibition in limiting retinal neurodegeneration in a model of NMDA (N-Methyl-D-aspartate)-induced excitotoxicity. Adult mice (8–10 weeks old) were given intravitreal injections (20 nmoles) of NMDA or NMLA (N-Methyl-L-aspartate, control). Intraperitoneal injection of MDL 72527 (40 mg/kg body weight/day) or vehicle (normal saline) was given 24 h before NMDA or NMLA treatment and continued until the animals were sacrificed (varied from 1 to 7 days). Analyses of retinal ganglion cell (RGC) layer cell survival was performed on retinal flatmounts. Retinal cryostat sections were prepared for immunostaining, TUNEL assay and retinal thickness measurements. Fresh frozen retinal samples were used for Western blotting analysis. A marked decrease in the neuronal survival in the RGC layer was observed in NMDA treated retinas compared to their NMLA treated controls, as studied by NeuN immunostaining of retinal flatmounts. Treatment with MDL 72527 significantly improved survival of NeuN positive cells in the NMDA treated retinas. Excitotoxicity induced neurodegeneration was also demonstrated by reduced levels of synaptophysin and degeneration of inner retinal neurons in NMDA treated retinas compared to controls. TUNEL labeling studies showed increased cell death in the NMDA treated retinas. However, treatment with MDL 72527 markedly reduced these changes. Analysis of signaling pathways during excitotoxic injury revealed the downregulation of pro-survival signaling molecules p-ERK and p-Akt, and the upregulation of a pro-apoptotic molecule BID, which were normalized with PAO inhibition. Our data demonstrate that inhibition of polyamine oxidase blocks NMDA-induced retinal neurodegeneration and promotes cell survival, thus offering a new therapeutic target for retinal neurodegenerative disease conditions.

Retinal Neuroprotection From Optic Nerve Trauma by Deletion of Arginase 2

Our previous studies have implicated expression of the mitochondrial isoform of the arginase enzyme arginase 2 (A2) in neurovascular injury during ischemic retinopathies. The aim of this study was to characterize the specific involvement of A2 in retinal injury following optic nerve crush (ONC). To accomplish this, wild-type (WT) or A2 knockout (A2^-/-) mice were subjected to ONC injury. The contralateral eye served as sham control. Quantitative RT-PCR and western blot were used to evaluate mRNA and protein expression. Retinal ganglion cell (RGC) survival was assessed in retinal whole mounts. Axonal sprouting was determined by anterograde transport of Cholera Toxin B (CTB). These analyses showed increased A2 expression following ONC. Numbers of NeuN-positive neurons as well as Brn3a- and RBPMS-positive RGC were decreased in the WT retinas at 14 days after ONC as compared to the sham controls. This ONC-induced neuronal loss was diminished in the A2^-/- retinas. Similarly, axonal degeneration was ameliorated by A2 deletion whereas axon sprouting was enhanced. Significant retinal thinning was also seen in WT retinas at 21 days after ONC, and this was blocked in A2^-/- mice. Cell death studies showed an increase in TUNEL positive cells in the RGC layer at 5 days after ONC in the WT retinas, and this was attenuated by A2 deletion. ONC increased glial cell activation in WT retinas, and this was significantly reduced by A2 deletion. Western blotting showed a marked increase in the neurotrophin, brain derived neurotrophic factor (BDNF) and its downstream signaling in A2^-/- retinas vs. WT after ONC. This was associated with increases in the axonal regeneration marker GAP-43 in A2^-/- retinas. Furthermore, A2^-/- retinas showed decreased NLRP3 inflammasome activation and lower interleukin (IL-) 1β/IL-18 levels as compared to WT retinas subjected to ONC. Collectively, our results show that deletion of A2 limits ONC-induced neurodegeneration and glial activation, and enhances axonal sprouting by a mechanism involving increases in BDNF and decreases in retinal inflammation. These data demonstrate that A2 plays an important role in ONC-induced retinal damage. Blockade of A2 activity may offer a therapeutic strategy for preventing vision loss induced by traumatic retinal injury.

Arginase 1 promotes retinal neurovascular protection from ischemia through suppression of macrophage inflammatory responses

The lack of effective therapies to limit neurovascular injury in ischemic retinopathy is a major clinical problem. This study aimed to examine the role of ureohydrolase enzyme, arginase 1 (A1), in retinal ischemia-reperfusion (IR) injury. A1 competes with nitric oxide synthase (NOS) for their common substrate l-arginine. A1-mediated l-arginine depletion reduces nitric oxide (NO) formation by NOS leading to vascular dysfunction when endothelial NOS is involved but prevents inflammatory injury when inducible NOS is involved. Studies were performed using wild-type (WT) mice, global A1^+/− knockout (KO), endothelial-specific A1 KO, and myeloid-specific A1 KO mice subjected to retinal IR injury. Global as well as myeloid-specific A1 KO mice showed worsened IR-induced neuronal loss and retinal thinning. Deletion of A1 in endothelial cells had no effect, while treatment with PEGylated (PEG) A1 improved neuronal survival in WT mice. In addition, A1^+/− KO mice showed worsened vascular injury manifested by increased acellular capillaries. Western blotting analysis of retinal tissue showed increased inflammatory and necroptotic markers with A1 deletion. In vitro experiments showed that macrophages lacking A1 exhibit increased inflammatory response upon LPS stimulation. PEG-A1 treatment dampened this inflammatory response and decreased the LPS-induced metabolic reprogramming. Moreover, intravitreal injection of A1 KO macrophages or systemic macrophage depletion with clodronate liposomes increased neuronal loss after IR injury. These results demonstrate that A1 reduces IR injury-induced retinal neurovascular degeneration via dampening macrophage inflammatory responses. Increasing A1 offers a novel strategy for limiting neurovascular injury and promoting macrophage-mediated repair.

RAS modulation prevents progressive cognitive impairment after experimental stroke: a randomized, blinded preclinical trial

Background

With the aging population, the prevalence and incidence of cerebrovascular disease will continue to rise, as well as the number of individuals with vascular cognitive impairment/dementia (VCID). No specific FDA-approved treatments for VCID exist. Although clinical evidence supports that angiotensin receptor blockers (ARBs) prevent cognitive decline in older adults, whether ARBs have a similar effect on VCID after stroke is unknown. Moreover, these agents reduce BP, which is undesirable in the acute stroke period, so we believe that giving C21 in this acute phase or delaying ARB administration would enable us to achieve the neurovascular benefits without the risk of unintended and potentially dangerous, acute BP lowering.

Methods

The aim of our study was to determine the impact of candesartan (ARB) or compound-21 (an angiotensin type 2 receptor––AT2R––agonist) on long-term cognitive function post-stroke, in spontaneously hypertensive rats (SHRs). We hypothesized that AT2R stimulation, either directly with C21, or indirectly by blocking the angiotensin type 1 receptor (AT1R) with candesartan, initiated after stroke, would reduce cognitive impairment. Animals were subjected to a 60-min transient middle cerebral artery occlusion and randomly assigned to either saline/C21 monotherapy, for the full study duration (30 days), or given sequential therapy starting with saline/C21 (7 days) followed by candesartan for the remainder of the study (21 days). Outcome measures included sensorimotor/cognitive-function, amyloid-β determination, and histopathologic analyses.

Results

Treatment with RAS modulators effectively preserved cognitive function, reduced cytotoxicity, and prevented chronic-reactive microgliosis in SHRs, post-stroke. These protective effects were apparent even when treatment was delayed up to 7 days post-stroke and were independent of blood pressure and β-amyloid accumulation.

Conclusion

Collectively, our findings demonstrate that RAS modulators effectively prevent cognitive impairment after stroke, even when treatment is delayed.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1262-x) contains supplementary material, which is available to authorized users.

Mechanisms of Diabetes-Induced Endothelial Cell Senescence: Role of Arginase 1

We have recently found that diabetes-induced premature senescence of retinal endothelial cells is accompanied by NOX2-NADPH oxidase-induced increases in the ureohydrolase enzyme arginase 1 (A1). Here, we used genetic strategies to determine the specific involvement of A1 in diabetes-induced endothelial cell senescence. We used A1 knockout mice and wild type mice that were rendered diabetic with streptozotocin and retinal endothelial cells (ECs) exposed to high glucose or transduced with adenovirus to overexpress A1 for these experiments. ABH [2(S)-Amino-6-boronohexanoic acid] was used to inhibit arginase activity. We used Western blotting, immunolabeling, quantitative PCR, and senescence associated β-galactosidase (SA β-Gal) activity to evaluate senescence. Analyses of retinal tissue extracts from diabetic mice showed significant increases in mRNA expression of the senescence-related proteins p16^INK4a, p21, and p53 when compared with non-diabetic mice. SA β-Gal activity and p16^INK4a immunoreactivity were also increased in retinal vessels from diabetic mice. A1 gene deletion or pharmacological inhibition protected against the induction of premature senescence. A1 overexpression or high glucose treatment increased SA β-Gal activity in cultured ECs. These results demonstrate that A1 is critically involved in diabetes-induced senescence of retinal ECs. Inhibition of arginase activity may therefore be an effective therapeutic strategy to alleviate diabetic retinopathy by preventing premature senescence.

Abstract TP88: Delayed Therapeutic Window for Prevention of Progressive Cognitive Impairment After Experimental Stroke

Background: With the aging population, the prevalence and incidence of cerebrovascular disease will continue to rise, as will the number of individuals with post-stroke cognitive impairment (PSCI). Unfortunately, no specific FDA approved treatments for PSCI exist. Although clinical trial evidence supports that renin angiotensin system (RAS) modulation by angiotensin receptor blockers (ARBs) prevent cognitive decline in older adults. The aim of our study was to determine the impact of the ARB candesartan or the AT2R agonist, C21, after stroke, on long-term cognitive function in spontaneously hypertensive rats (SHRs).

Methods: Thirty three SHRs were subjected to a 60 minute transient middle cerebral artery occlusion (MCAO) and randomly assigned to either Saline/ C21 (0.3 mg/kg, IP) only or Saline/ C21 (7 days) followed by candesartan (0.3 mg/kg) IP for the remainder of the study. Outcome measures included sensorimotor and cognitive function, performed using a sequence of blinded tests, and assessed at baseline and up to 28 days post-stroke. Animals were sacrificed at 30 days and their brains collected for amyloid-β protein determination and histopathologic analyses.

Results: Chronic administration of C21, or candesartan prevented PSCI, even when treatment was initiated at 7 days after the ischemic insult. The groups treated with C21 and candesartan demonstrated superior performance on the novel NOR test, compared to saline treated animals. C21 (first 7 days) only or C2 and candesartan treatments had markedly lower hippocampal concentrations of Aβ1-42 at 30 days post-stroke than those treated with saline. Sensorimotor deficits (Bederson and beam walk scores) were pronounced at 24 h post-stroke and all treatment groups showed similar recovery at 28 days post stroke. C21 had no effect on BP compared to saline-treated controls.

Conclusion: Collectively, our findings demonstrate that RAS modulators effectively prevent PSCI, even when treatment is delayed.

Obesity-induced vascular dysfunction and arterial stiffening requires endothelial cell arginase 1

AIMS

Elevation of arginase activity has been linked to vascular dysfunction in diabetes and hypertension by a mechanism involving decreased nitric oxide (NO) bioavailability due to L-arginine depletion. Excessive arginase activity also can drive L-arginine metabolism towards the production of ornithine, polyamines, and proline, promoting proliferation of vascular smooth muscle cells and collagen formation, leading to perivascular fibrosis. We hypothesized that there is a specific involvement of arginase 1 expression within the vascular endothelial cells in this pathology.

METHODS AND RESULTS

To test this proposition, we used models of type 2 diabetes and metabolic syndrome. Studies were performed using wild type (WT), endothelial-specific arginase 1 knockout (EC-A1-/-) and littermate controls(A1con) mice fed high fat-high sucrose (HFHS) or normal diet (ND) for 6 months and isolated vessels exposed to palmitate-high glucose (PA/HG) media. Some WT mice or isolated vessels were treated with an arginase inhibitor, ABH [2-(S)-amino-6-boronohexanoic acid. In WT mice, the HFHS diet promoted increases in body weight, fasting blood glucose, and post-prandial insulin levels along with arterial stiffening and fibrosis, elevated blood pressure, decreased plasma levels of L-arginine, and elevated L-ornithine. The HFHS diet or PA/HG treatment also induced increases in vascular arginase activity along with oxidative stress, reduced vascular NO levels, and impaired endothelial-dependent vasorelaxation. All of these effects except obesity and hypercholesterolemia were prevented or significantly reduced by endothelial-specific deletion of arginase 1 or ABH treatment.

CONCLUSION

Vascular dysfunctions in diet-induced obesity are prevented by deletion of arginase 1 in vascular endothelial cells or arginase inhibition. These findings indicate that upregulation of arginase 1 expression/activity in vascular endothelial cells has an integral role in diet-induced cardiovascular dysfunction and metabolic syndrome.

Minocycline in Acute Cerebral Hemorrhage: An Early Phase Randomized Trial

BACKGROUND AND PURPOSE

Minocycline is under investigation as a neurovascular protective agent for stroke. This study evaluated the pharmacokinetic, anti-inflammatory, and safety profile of minocycline after intracerebral hemorrhage.

METHODS

This study was a single-site, randomized controlled trial of minocycline conducted from 2013 to 2016. Adults ≥18 years with primary intracerebral hemorrhage who could have study drug administered within 24 hours of onset were included. Patients received 400 mg of intravenous minocycline, followed by 400 mg minocycline oral daily for 4 days. Serum concentrations of minocycline after the last oral dose and biomarkers were sampled to determine the peak concentration, half-life, and anti-inflammatory profile.

RESULTS

A total of 16 consecutive eligible patients were enrolled, with 8 randomized to minocycline. Although the literature supports a time to peak concentration (T_max) of 1 hour for oral minocycline, the T_max was estimated to be at least 6 hours in this cohort. The elimination half-life (available on 7 patients) was 17.5 hours (SD±3.5). No differences were observed in inflammatory biomarkers, hematoma volume, or perihematomal edema. Concentrations remained at neuroprotective levels (>3 mg/L) throughout the dosing interval in 5 of 7 patients.

CONCLUSIONS

In intracerebral hemorrhage, a 400 mg dose of minocycline was safe and achieved neuroprotective serum concentrations. However, oral administration led to delayed absorption in these critically ill patients and should not be used when rapid, high concentrations are desired. Given the safety and pharmacokinetic profile of minocycline in intracerebral hemorrhage and promising data in the treatment of ischemic stroke, intravenous minocycline is an excellent candidate for a prehospital treatment trial.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01805895.

Abstract WP113: Dose-response and Therapeutic Time-window of Compound 21: a Randomized Preclinical Trial in Rat Model of Thromboembolic Stroke

Background: We and others have previously shown promising results with the use of the angiotensin type 2 receptor agonist, compound 21 (C21), in experimental stroke. Here we aimed to determine the best dose and time window for C21 in a clinically relevant embolic stroke model.

Methods: This study was conducted as a translational, randomized, controlled, blinded preclinical trial with the guidance of our biostatistician. Male Wistar rats (8-9 weeks old) were subjected to embolic middle cerebral artery occlusion (eMCAO). For the dose-response study, animals received C21 (0.01, 0.03 and 0.06 mg/kg/d) or saline (orally) for 5 days, with the first dose given IV at 3 h post-eMCAO. For the time-window study, the optimal dose of C21 was initiated at 3, 6 or 24 h post-eMCAO and daily thereafter, for 5 days. Behavioral outcomes (Bederson, paw grasp and grip strength) were blindly assessed at days, 1, 3, 5 and 7. Rats were then sacrificed and their brains collected for infarct size and vascular density analyses. Results (Table): In the dose-response study, repeated-measures ANOVA showed significant (p < 0.05) behavioral improvement with the low dose (0.01 mg/kg). This dose was associated with higher vascularity in the ischemic penumbra, detected by laminin staining, compared to saline treated controls (65±6 vs 46±7 p < 0.05). In the time-window study, the 0.01 mg/kg dose displayed non-statistically significant improvements when given 3 h and 6 h after eMCAO. There were no differences between doses or time-windows for either % infarct size or tissue loss.

Conclusions: C21 given at 0.01 mg/kg/d was effective in improving behavioral dysfunction after embolic stroke when administered within 6 h. Compound C21 shows promise as a potential therapeutic agent and should be examined for safety and efficacy in clinical trials for ischemic stroke.

Abstract WP101: Involvement of the Contralesional Angiotensin Type 2 Receptor in Compound 21 Mediated Functional Recovery After Stroke

Introduction: We have recently shown that the angiotensin type 2 receptor (AT2R) agonist, compound 21 (C21), provides sustained functional recovery after ischemic stroke. This was associated with upregulation of the AT2R and the neurotrophin, brain derived neurotrophic factor (BDNF), in the contralesional brain hemisphere. Here, we aimed to study the contribution of this hemisphere in C21 mediated functional recovery after stroke through localized knockdown of the AT2R.

Methods: male wistar rats (34) received two intrastriatal injections of short hairpin RNA (shRNA) lentiviral particles against AT2R, or non-targeting control vector (NTC) into the left brain hemisphere to achieve localized AT2R knockdown. After 14 days, rats were subjected to 90 minutes right middle cerebral artery occlusion (MCAO) and received either C21 (0.03 mg/kg) or saline at reperfusion (IV) then daily (IP) for 7 days. Rats were blindly assessed for behavioral outcome up to 10 days as well as molecular analysis. Results (table): PCR and Western blotting confirmed successful knockdown of the AT2R in the left (contralesional) hemisphere by about 50%. All groups showed worsened outcome on days 1 to 3 then recovered on days 7 to 10. The C21/NTC group showed better behavioral outcome compared to other groups at days 7 and 10, while the saline/shRNA group was associated with the least recovery. Using Western blotting, C21/NTC group showed higher BDNF and lower proBDNF (pro-form) levels in the ischemic and contralesional hemispheres respectively. Expression of the pro-apoptotic P75NTR receptor of proBDNF was decreased with C21 treatment irrespective of AT2R knockdown.

Conclusion: Contralesional AT2R could be involved in C21 mediated functional recovery after stroke.

Brain-Derived Neurotrophic Factor Knockdown Blocks the Angiogenic and Protective Effects of Angiotensin Modulation After Experimental Stroke

Angiotensin type 1 receptor blockers (ARBs) have been shown to be neuroprotective and neurorestorative in experimental stroke. The mechanisms proposed include anti-inflammatory, antiapoptotic effects, as well as stimulation of endogenous trophic factors leading to angiogenesis and neuroplasticity. We aimed to investigate the involvement of the neurotrophin, brain-derived neurotrophic factor (BDNF), in ARB-mediated functional recovery after stroke. To achieve this aim, Wistar rats received bilateral intracerebroventricular (ICV) injections of short hairpin RNA (shRNA) lentiviral particles or nontargeting control (NTC) vector, to knock down BDNF in both hemispheres. After 14 days, rats were subjected to 90-min middle cerebral artery occlusion (MCAO) and received the ARB, candesartan, 1 mg/kg, or saline IV at reperfusion (one dose), then followed for another 14 days using a battery of behavioral tests. BDNF protein expression was successfully reduced by about 70 % in both hemispheres at 14 days after bilateral shRNA lentiviral particle injection. The NTC group that received candesartan showed better functional outcome as well as increased vascular density and synaptogenesis as compared to saline treatment. BDNF knockdown abrogated the beneficial effects of candesartan on neurobehavioral outcome, vascular density, and synaptogenesis. In conclusion, BDNF is directly involved in candesartan-mediated functional recovery, angiogenesis, and synaptogenesis.

Sequential Therapy with Minocycline and Candesartan Improves Long-Term Recovery After Experimental Stroke

Minocycline and candesartan have both shown promise as candidate therapeutics in ischemic stroke, with multiple, and somewhat contrasting, molecular mechanisms. Minocycline is an anti-inflammatory, antioxidant, and anti-apoptotic agent and a known inhibitor of matrix metalloproteinases (MMPs). Yet, minocycline exerts antiangiogenic effects both in vivo and in vitro. Candesartan promotes angiogenesis and activates MMPs. Aligning these therapies with the dynamic processes of injury and repair after ischemia is likely to improve success of treatment. In this study, we hypothesize that opposing actions of minocycline and candesartan on angiogenesis, when administered simultaneously, will reduce the benefit of candesartan treatment. Therefore, we propose a sequential combination treatment regimen to yield a better outcome and preserve the proangiogenic potential of candesartan. In vitro angiogenesis was assessed using human brain endothelial cells. In vivo, Wistar rats subjected to 90-min middle cerebral artery occlusion (MCAO) were randomized into four groups: saline, candesartan, minocycline, and sequential combination of minocycline and candesartan. Neurobehavioral tests were performed 1, 3, 7, and 14 days after stroke. Brain tissue was collected on day 14 for assessment of infarct size and vascular density. Minocycline, when added simultaneously, decreased the proangiogenic effect of candesartan treatment in vitro. Sequential treatment, however, preserved the proangiogenic potential of candesartan both in vivo and in vitro, improved neurobehavioral outcome, and reduced infarct size. Sequential combination therapy with minocycline and candesartan improves long-term recovery and maintains candesartan's proangiogenic potential.

Cellular connections, microenvironment and brain angiogenesis in diabetes: Lost communication signals in the post-stroke period

Diabetes not only increases the risk but also worsens the motor and cognitive recovery after stroke, which is the leading cause of disability worldwide. Repair after stroke requires coordinated communication among various cell types in the central nervous system as well as circulating cells. Vascular restoration is critical for the enhancement of neurogenesis and neuroplasticity. Given that vascular disease is a major component of all complications associated with diabetes including stroke, this review will focus on cellular communications that are important for vascular restoration in the context of diabetes. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Abstract 31: The Angiotensin Type 2-receptor Agonist, Compound 21, Provides Neuroprotection After Ischemia Reperfusion Injury Through Interleukin 10 Upregulation

Introduction: We and others have shown that the angiotensin type 2 (AT2) receptor agonist, compound 21 (C21), provides neuroprotection and enhances recovery in rodent stroke models yet the mechanism involved is not known. Moreover, C21 treatment is associated with an anti-inflammatory response. Here we tested the hypothesis that C21 mediates neuroprotection by upregulating the neuroprotective and anti-inflammatory cytokine interleukin (IL)-10. Methods: Wistar rats (n=16) were subjected to 3 h MCA suture occlusion and treated at reperfusion with C21 (0.03 mg/kg) ± IL-10 neutralizing antibody (0.1 μg/kg) both given I.P. Endpoints at 24 h included: Infarct size, behavioral outcome, and molecular analysis. Primary rat neurons were used to test the direct neuroprotective effect of C21 in vitro. Results (Table): C21 treatment upregulated IL-10 expression (1797±89 vs 1333±84 pg/mg) and increased IL-10 downstream survival signals, STAT3 and AKT phosphorylation, in the stroked hemisphere compared to saline. Anti-IL-10 co-treatment blocked the C21 induced reduction in infarct size and inflammatory/apoptotic markers, and blunted the improvement in behavioral outcome, as well as survival signal activation. In vitro (n=4), C21 treatment failed to directly protect ischemic neurons against oxygen glucose deprivation/reperfusion (OGD/R) insult as measured by LDH release (other cell death markers are to be analyzed), but was able to upregulate IL-10 in normoxic neurons (0.3±0.02 vs 0.23±0.01) suggesting a potential indirect neuroprotective effect. Conclusion: C21 provides acute neuroprotection after ischemia reperfusion injury through neuronal IL-10 upregulation. Further understanding of the mechanism of action will pave the way for translating C21 and future AT2 agonists to the clinical stroke setting.

Abstract 307: Enhancement of Cerebrovascular Relaxation by Angiotensin II Type 2 Receptor Agonist, C21, is Lost in Type 2 Diabetes

Background: Angiotensin type 1 receptor (AT1R) blockers provide vascular protection and improve stroke outcomes in young otherwise healthy animals. These effects are believed to be mediated by the indirect stimulation of AT2R signaling. The AT2R agonist, compound 21 (C21), improves endothelial function in peripheral vascular beds but its effect on cerebral endothelial function remains unknown. It is important to determine the vascular effects of C21 in diabetes, a comorbid condition which is known to worsen stroke outcomes.

Methods: Endothelium-dependent relaxation was assessed in male Wistar and Type 2 diabetic Goto-Kakizaki (GK) rats (n=3-6) by measuring acetylcholine (ACh, 1 nM - 5 μm) induced dilatory response in basilar arteries. In a subset of experiments C21 dose response curves were generated (0.1 nM - 1 μM) or vessels were pre-incubated with 100 nM C21 ± 1 μM PD123319 (AT2R blocker) for 30 min prior to Ach dose response curves. Area under the curve (AUC) and half maximal effective concentration (EC50 nM) were calculated as indices of total relaxation and receptor sensitivity, respectively. Angiotensin receptors expression was measured by immunoblotting of brain homogenates.

Results: AT2R agonist C21 dose response curves showed no basilar reactivity in either control or diabetic animals. Pre-incubation with C21 enhanced relaxation to Ach in control animals (vehicle 146.7 ± 3.9 vs C21 pretreatment 229.6 ± 11.6), which was abolished by the blockade of AT2R (176.9 ± 25.5, p=0.007). Similarly, C21 improved sensitivity in control animals (vehicle 110.5 ± 32 vs C21 pretreatment 11.9 ± 2) which was abolished in the presence of PD123319 (93.8 ± 31, p=0.04). Basilar artery relaxation (AUC) was impaired in diabetic GK rats (93.9 ± 1.8%) as compared to controls (146.7 ± 3.9%) and C21 had no effect (98 ± 8.9%) indicating a disease and treatment interaction (p<0.001). Normalized AT1R expression levels were 1 ± 0.04 and 0.98 ± 0.05 in control vs diabetic rats and respective AT2R levels were 1 ± 0.1 and 0.84 ± 0.09.

Conclusion: C21 improves vascular relaxation in control but not in diabetic rats in an AT2R-dependent manner. Underlying mechanisms blunting response to C21 need to be further investigated and may impact the subsequent development of C21 as a treatment for stroke.

Low-dose candesartan enhances molecular mediators of neuroplasticity and subsequent functional recovery after ischemic stroke in rats

We have previously reported that angiotensin type 1 receptor (AT1R) blockade with candesartan exerts neurovascular protection after experimental cerebral ischemia. Here, we tested the hypothesis that a low, subhypotensive dose of candesartan enhances neuroplasticity and subsequent functional recovery through enhanced neurotrophic factor expression in rats subjected to ischemia reperfusion injury. Male Wistar rats (290-300 g) underwent 90 min of middle cerebral artery occlusion (MCAO) and received candesartan (0.3 mg/kg) or saline at reperfusion and then once every 24 h for 7 days. Functional deficits were assessed in a blinded manner at 1, 3, 7, and 14 days after MCAO. Animals were sacrificed 14-day post-stroke and the brains perfused for infarct size by cresyl violet. Western blot and immunohistochemistry were used to assess the expression of growth factors and synaptic proteins. Candesartan-treated animals showed a significant reduction in the infarct size [t (13) = -5.5, P = 0.0001] accompanied by functional recovery in Bederson [F (1, 13) = 7.9, P = 0.015], beam walk [F (1, 13) = 6.7, P = 0.023], grip strength [F (1, 13) = 15.2, P = 0.0031], and rotarod performance [F (1, 14) = 29.8, P < 0.0001]. In addition, candesartan-treated animals showed significantly higher expression of active metalloproteinase-3 (MMP-3), laminin, and angiopoietin-1 (Ang-1). The expression of vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) and its receptor was significantly increased in the animals treated with candesartan. Also, we observed significant increases in neuroplasticity markers, synaptophysin, and PSD-95. These results indicate that low-dose candesartan had a large and enduring effect on measures of plasticity, and this accompanied the functional recovery after ischemic stroke.

Cerebral neovascularization in diabetes: implications for stroke recovery and beyond

Neovascularization is an innate physiologic response by which tissues respond to various stimuli through collateral remodeling (arteriogenesis) and new vessel formation from existing vessels (angiogenesis) or from endothelial progenitor cells (vasculogenesis). Diabetes has a major impact on the neovascularization process but the response varies between different organ systems. While excessive angiogenesis complicates diabetic retinopathy, impaired neovascularization contributes to coronary and peripheral complications of diabetes. How diabetes influences cerebral neovascularization remained unresolved until recently. Diabetes is also a major risk factor for stroke and poor recovery after stroke. In this review, we discuss the impact of diabetes, stroke, and diabetic stroke on cerebral neovascularization, explore potential mechanisms involved in diabetes-mediated neovascularization as well as the effects of the diabetic milieu on poststroke neovascularization and recovery, and finally discuss the clinical implications of these effects.

Anti-inflammatory IL-10 is upregulated in both hemispheres after experimental ischemic stroke: Hypertension blunts the response

Background

Exogenous administration of the anti-inflammatory cytokine, interleukin 10 (IL-10), is known to promote neuroprotection and mitigate neuroinflammation after ischemia. However, endogenous expression and localization of IL-10 and its receptor (IL-10R) in the post-ischemic brain are still to be elucidated. In this investigation we aimed at determining the temporospatial expression of IL-10 in the rat brain relative to its systemic levels after ischemic stroke.

Methods

Wistar rats were subjected to either permanent (pMCAO) or 3-h temporary (tMCAO) middle cerebral artery occlusion and euthanized at either 24 or 72 h. IL-10/IL-10R levels were quantified in ischemic and contralesional hemispheres and compared to shams using multiplex bead array and Western blotting, respectively. Localization of IL-10/IL-10R with markers for neurons, microglia, astrocytes & endothelial cells were examined using double labeling immunofluorescence. IL-10 was also quantified in the brain tissue of spontaneously hypertensive rats (SHRs) at 24 h after tMCAO.

Results

After both pMCAO and tMCAO in Wistars, IL-10 was significantly upregulated in both hemispheres by ≈ 50% at 24 h while IL-10R expression was significantly decreased only at 72 h in the ischemic hemisphere. IL-10 and IL-10R expression highly co-localized with viable neurons in the ischemic penumbra and contralesional hemisphere. In hypertensive rats, IL-10 showed no significant contralesional upregulation and declined significantly in the ischemic side at 24 h post-ischemia.

Conclusion

Our data highlights the involvement of the ischemic and contralesional neurons in the endogenous anti-inflammatory response after ischemic stroke through increased production of IL-10. This increase in IL-10 is blunted in hypertensive animals and may contribute to worse outcomes.