Cerebral vasospasm (CV) and related ischemic injury is a major contributor to death and disability after aneurysmal subarachnoid hemorrhage (aSAH). Our overall goal is to understand molecular mechanisms of action of endogenous mechano-growth factor (MGF), a splice variant of insulin-like growth factor 1 (IGF-1), in the brain. MGF was found to be neuroprotective after stroke in a gerbil model of ischemic injury and may serve as a potential therapeutic target to prevent CV-induced brain damage. In our studies, we characterized hypoxia induced changes in MGF expression in different brain regions, commonly affected by CV, at different time points (from 2 hours to 7 days) post 4h hypoxia treatments (6, 8,10 or 12% oxygen). The brain regions analyzed were motor cortex, hippocampus, striatum and hypothalamus. In addition, we characterized changes in MGF expression in microparticle (MP) fractions isolated from cerebrospinal fluid (CSF) extracted from CV patients. Microparticle fractions were isolated from CSF samples using serial ultracentrifugation. We used real time RT-PCR, western blots, and enzyme immunosorbent assay to quantify changes in gene expression and protein levels.
In the animal model, our results showed that there were time, dose and brain region specific changes in MGF expression that correlated with changes in the expression of heme oxygenase 1 (HO-1) and biliverdin reductase A, which are molecules involved in neuroprotection, and caspases, apoptotic markers. These results suggest that changes in endogenous MGF due to hypoxia may activate neuroprotective pathways in the brain. In CSF MPs isolated from CV patients, we observed an increase in MGF expression that correlated with the CV onset window and with an increase in HO-1, suggesting that similar pathways are activated post-CV in humans and post-hypoxia in animals. These data indicate that endogenous MGF may play a role in CV onset and may be a neuroprotective target in CV papteins. However, further studies are required to elucidate the molecular mechanisms of MGF and its exact role in CV development and patient outcome.