Targeting miR-21 in spinal cord injuries: a game-changer?

Spinal cord injury (SCI) is a devastating neurological state causing physical disability, psychological stress and financial burden. SCI global rate is estimated between 250,000 and 500,000 individuals every year, of which 60% of victims are young, healthy males between 15 and 35 years. A variety of pathological conditions such as neuroinflammation, mitochondrial dysfunction, apoptosis, glial scar formation, blood-spinal cord barrier disruption, and angiogenesis disruption occur after SCI leading to a limitation in recovery. MicroRNAs (miRs) are endogenous and non-coding RNAs consisting of 22 nucleotides that regulate 60% of all human genes and involve several normal physiological processes and pathological conditions. miR-21 is among the most highly expressed miRs and its expression has been shown to increase one day after SCI and this elevation is sustained up to 28 days after injury. Overexpression of miR-21 exerts many protective effects against SCI by inhibiting neuroinflammation, improving blood-spinal cord barrier function, regulating angiogenesis, and controlling glial scar formation. It also exhibits anti-apoptotic effects in SCI by down-regulating the expression of PTEN, Spry2, and PDCD4. This review provides a novel therapeutic perspective for miR-21 in SCI.