Pleiotropic Role of PPARγ in Intracerebral Hemorrhage: An Intricate System Involving Nrf2, RXR, and NF-κB

Intracerebral hemorrhage (ICH) is a subtype of stroke involving formation of hematoma within brain parenchyma, which accounts for 8-15% of all strokes in Western societies and 20-30% among Asian populations, and has a 1-year mortality rate >50%. The high mortality and severe morbidity make ICH a major public health problem. Only a few evidence-based targeted treatments are used for ICH management, and interventions focus primarily on supportive care and comorbidity prevention. Even in patients who survive the ictus, extravasated blood (including plasma components) and subsequent intrahematoma hemolytic products trigger a series of adverse events within the brain parenchyma, leading to secondary brain injury, edema and severe neurological deficits or death. Although the hematoma in humans gradually resolves within months, full restoration of neurological function can be slow and often incomplete, leaving survivors with devastating neurological deficits. During past years, peroxisome proliferator-activated receptor gamma (PPAR) transcription factor and its agonists received recognition as important players in regulating not only glucose and lipid metabolism (which underlies its therapeutic effect in type 2 diabetes mellitus), and more recently, as an instrumental pleiotropic regulator of antiinflammation, antioxidative regulation, and phagocyte-mediated cleanup processes. PPAR agonists have emerged as potential therapeutic target for stroke. The use of PPAR as a therapeutic target appears to have particularly strong compatibility toward pathogenic components of ICH. In addition to its direct genomic effect, PPAR may interact with transcription factor, NF-B, which may underlie many aspects of the antiinflammatory effect of PPAR. Furthermore, PPAR appears to regulate expression of Nrf2, another transcription factor and master regulator of detoxification and antioxidative regulation. Finally, the synergistic costimulation of PPAR and retinoid X receptor, RXR, may play an additional role in the therapeutic modulation of PPAR function. In this article, we outline the main components of the role of PPAR in ICH pathogenesis.