NADPH Oxidase and Angiogenesis Following Endothelin-1 Induced Stroke in Rats: Role for Nox2 in Brain Repair

Abstract

NADPH oxidases contribute to brain injury, yet they may also have a role in brain repair, particularly in vascular signaling and angiogenesis. This study determined the temporal and spatial profile of NADPH oxidase subunit expression/activity concurrently with angiogenesis in the brain following transient ischemic stroke induced by prolonged constriction of the middle cerebral artery by perivascular injection of endothelin-1 in conscious Hooded Wistar rats (n = 47). VEGF mRNA expression was increased in the ipsilateral cortex and striatum between 6 h and 28 days post-stroke concurrently with a marked increase in Nox2 mRNA expression up to 7 days, and increased Nox4 mRNA expression detected between 7 and 28 days. Point counting of blood vessels using Metamorph imaging software showed increased vascular sprouting between 3 and 7 days after stroke with new vascular networks detected in the core infarct region by 14 days. Angiogenic blood vessels 3 and 7 days post-stroke were observed to co-localise with both Nox2 antibody and dihydroethidium fluorescence suggesting a role for Nox2 generated superoxide during the phase of vascular remodeling, whilst Nox4 expression was detected once new cerebral vessels had formed. These results indicate for the first time that ROS signaling through a cerebrovascular Nox2 NADPH oxidase may be important in initiating brain angiogenesis.

Brain Remodelling following Endothelin-1 Induced Stroke in Conscious Rats

“…Indeed we have previously reported that with spontaneous functional recovery newly formed vascular networks are detected within damaged regions [5]. One possible mechanism may be associated with the damage sustained to cerebral blood vessels themselves, such that a greater degree of vascular sprouting may result from an increased number of damaged vessels.…”

A 24 h Delay in the Redox Response Distinguishes the most Severe Stroke Patients from Less Severe Stroke Patients

“…The distribution of tPA use was proportionate and met expected frequencies across IS etiologies, NIHSS groups, MRS and discharge statuses (x 2 =1.96, 7.56, 4.15, 0.05 respectively, p>0.05 for all) suggesting no interactive effects with the above results. Cerebral vascular tone is adjusted through the production of oxygenbased radicals via the activity of NADPH-oxidase enzymes (NOX) [18][19][20]. In rat models of stroke, NOX, and thus oxygen-based radicals, increase within hours of occlusion and co-localize with anigiogenesis [20,21].…”

Challenges and Pitfalls Associated with Stem Cell Transplants for Stroke

“…Perhaps it is this reason that early clinical trials chose not to implant sooner than 6 months after stroke to avoid the acute phase associated with toxicity and infarct expansion [11]. However recent studies suggest that this late time may not be optimal either due to extensive glial scar formation and loss of factors that are known to support cell survival [12].…”

“…During the acute phase of stroke, microglia are activated within minutes, with peak inflammatory cell infiltration detected in animal models by 7 days [12,13], contributing to injury through several mechanisms. Astrogliosis is also detected between 3 and 7 days after stroke with evidence of gliotic scar formation commencing around the infarct border by 14 days, which thickens to eventually occupy the core infarct [12,14]. The neurovascular unit is also damaged primarily by reduced blood flow and secondarily by ensuing inflammatory processes.…”

“…The neurovascular unit is also damaged primarily by reduced blood flow and secondarily by ensuing inflammatory processes. Vascular recovery in the form of angiogenesis is detected early after stroke and has been implicated in supporting brain regeneration, but new vascular networks are not evident until at least 14 days [12], and then later regress by 6 months if recovery is not achieved [15]. Collectively, these factors contribute to an environment that is challenging for neuronal survival, repair and replacement: timing is thus one of the most crucial factors for consideration in transplant studies.…”