Intracerebral hemorrhage (ICH) is the primary event in about 10% of strokes, and has high morbidity and mortality rates. In addition to its mass effect, experimental evidence indicates that release of toxins such as hemoglobin from the hematoma contributes to cell loss in adjacent tissue. Cellular vulnerability to hemoglobin is largely a function of the activity of the heme oxygenase (HO) enzymes, which consist of inducible HO-1 and constitutively-expressed HO-2. HO activity has antioxidant and anti-inflammatory effects due to heme/hemin removal and generation of two breakdown products, biliverdin (converted to bilirubin by biliverdin reductase) and carbon monoxide. Prior studies have demonstrated that HO-1 overexpression by cultured astrocytes provides robust protection against heme-mediated injury, while HO-1 knockout is deleterious. In vivo, initial results indicate that transgenic mice overexpressing HO-1 in astrocytes sustain significantly less mortality and blood-brain barrier disruption after experimental ICH than their wild-type counterparts. Furthermore, systemic treatment with HO-1 inducers increases HO-1 in perivascular astrocytes and is also protective. The broad goal of this project is to further define the therapeutic potential of astrocyte HO-1 overexpression after ICH, using specific genetic methods for proof of concept followed by randomized blinded trials of translationally-relevant pharmacotherapies. Our experimental aims are as follows: 1) Produce striatal hematomas in wild-type (WT), GFAP-Cre-HMOX1fl/fl (astrocyte HO-1 KO), and GFAP.HMOX1 mice (astrocyte HO-1 overexpression) by stereotactic injection of blood or collagenase. Compare mortality, blood-brain barrier breakdown, striatal cell loss, inflammatory response, and behavioral/cognitive outcome. 2) Quantify perihematomal blood flow, oxygen saturation, and hematoma size in WT, GFAP-Cre-Hmox1fl/fl and GFAP.HMOX1 mice after ICH using micro ultrasound combined with photoacoustic imaging. Quantify blood vessels with unbiased histological analysis guided by design-based stereology. 3) Randomize GFAP-Cre- Hmox1fl/fl mice and Hmox1fl/fl controls to treatment with HO-1 inducers (sulforaphane, hemin) or vehicle, administered i.p. beginning 3 hours after striatal blood or collagenase injection. Quantify the effect on outcome as described above. It is hoped that completion of these aims will establish the benefit of astrocyte HO-1 overexpression after spontaneous ICH, and also demonstrate the feasibility of accomplishing this end with selected pharmacotherapies. This information will then provide the rational basis for clinical trials of novel agents for a stroke subtype that currently has few therapeutic options and a grim prognosis.
The results of these experiments may lead to identification of an important protective mechanism after stroke that is caused by hemorrhage into the brain. It is hoped that therapies that enhance expression of heme oxygenase-1 in astrocytes will reduce cell injury in tissue surrounding the blood clot. The death rate for this type of stroke may then be reduced, and the chance of returning to an independent and productive life may be increased.
| Chen-Roetling, Jing; Regan, Kathleen A; Regan, Raymond F (2018) Protective effect of vitreous against hemoglobin neurotoxicity. Biochem Biophys Res Commun 503:152-156 |
| Chen-Roetling, Jing; Ma, Sheng-Kai; Cao, Yang et al. (2018) Hemopexin increases the neurotoxicity of hemoglobin when haptoglobin is absent. J Neurochem 145:464-473 |
| Chen-Roetling, Jing; Kamalapathy, Pramod; Cao, Yang et al. (2017) Astrocyte heme oxygenase-1 reduces mortality and improves outcome after collagenase-induced intracerebral hemorrhage. Neurobiol Dis 102:140-146 |
| Chen-Roetling, Jing; Regan, Raymond F (2017) Targeting the Nrf2-Heme Oxygenase-1 Axis after Intracerebral Hemorrhage. Curr Pharm Des 23:2226-2237 |
| Chen-Roetling, Jing; Regan, Raymond F (2016) Haptoglobin increases the vulnerability of CD163-expressing neurons to hemoglobin. J Neurochem 139:586-595 |
