Temporal and spatial expression of cyclin H in rat spinal cord injury.

Cyclin H regulates cell cycle transitions; it always forms trimeric cyclin-dependent protein kinases (CDK)-activating kinase (CAK) complex with CDK7 and MAT1 that phosphorylates a threonine residue in the CDK2 T loop region. However, neither the expression nor function of cyclin H in the central nervous system (CNS) injury is still clear. Therefore, we studied cyclin H in a rat spinal cord contusion model. Injury markedly increased cyclin H protein expression throughout the thoracic spinal cord but did not increase CDK7. However, double immunofluorescent staining for proliferating cell nuclear antigen (PCNA) and cell markers revealed increases of cyclin H and CDK2 in proliferating microglia and astrocytes, and the co-immunoprecipitation studies shown that the associations of cyclin H with CDK2 were enhanced evidently after injury. Our data suggest that cyclin H may play a proliferative role in spinal cord injury (SCI).