MicroRNAs as brain injury biomarker

MicroRNAs (miRNAs) are small, noncoding endogenous RNA regulatory molecules, which modulate gene expression either by mRNA degradation or translation suppression. MiRNAs in serum are resistant to repeated freeze thaw, enzymatic degradation and can survive extreme pH conditions. Due to these properties, miRNAs have the advantage over protein-based biomarkers and have recently emerged as novel biomarkers for many diseases and disorders. Worldwide, brain injuries caused by traumatic brain injury (TBI), cerebral ischemia, and stroke are the leading causes of death and disability. TBI is classified as mild, moderate, or severe depending on the severity and the cause of injury to the brain. Cerebral ischemia can be further classified as global or focal. Stroke is caused by obstruction of blood flow in brain vessels and its disruption leads to hemorrhage. Mild brain injuries such as mild TBI and mild ischemic insults can often go undiagnosed and untreated due to the lack of immediate visible symptoms. Current diagnostic techniques including imaging are not capable of detecting low-level trauma to the brain. Recent studies on unique changes in expression of miRNAs in serum and brain samples after TBI or stroke show great promise of developing them as noninvasive test for brain injury. In this chapter, the recent progress of miRNAs in brain injuries has been reviewed especially for their utility as biomarker. The various methods that are currently being followed for identifying the altered expression of miRNAs in brain injuries and their analysis has also been discussed. In addition to the diagnostic and prognostic biomarkers, the brain injury-altered miRNAs have the potential to be used in therapeutics and are discussed with special emphasis on TBI and cerebral ischemia.