CyclinD1-RNAi were administered to 8–12 weeks C57BL/6 J mice through intranasal route using in vivo-jetPEI. Briefly, either the cyclinD1 RNAi or control RNAi along with JetPEI were separately diluted into half the injection volume in a 10% sterile glucose solution where the final glucose concentration would have to be 5% (N/P ratio of 7). Both the solutions were mixed by slight vortexing, and the JetPEI-RNAi mixture was incubated 15 min at room temperature. Intranasal administration of the Jet-PEI complex was performed 30 min after either sham or TBI surgery with the pipette tip to each nostril of the mouse. A 5μl of the jetPEI-RNAi complex was slowly administered to the nostrils maintaining a 2–3 s interval up to 10μl total/nostril of a mouse. After 5–10 s another 10μl of the solution was administered to the other nostril following the similar way for a total of 20μl/mouse and 10μg of siRNA/mouse.

Cell cycle activation has been associated with varying types of neurological disorders including brain injury. Cyclin D1 is a critical modulator of cell cycle activation and upregulation of Cyclin D1 in neurons contributes to the pathology associated with traumatic brain injury (TBI). Mitochondrial mass is a critical factor to maintain the mitochondrial function, and it can be regulated by different signaling cascades and transcription factors including NRF1. However, the underlying mechanism of how TBI leads to impairment of mitochondrial mass following TBI remains obscure. Our results indicate that augmentation of CyclinD1 attenuates mitochondrial mass formation following TBI. To elucidate the molecular mechanism, we found that Cyclin D1 interacts with a transcription factor NRF1 in the nucleus and prevents NRF1's interaction with p300 in the pericontusional cortex following TBI. As a result, the acetylation level of NRF1 was decreased, and its transcriptional activity was attenuated. This event leads to a loss of mitochondrial mass in the pericontusional cortex following TBI. Intranasal delivery of Cyclin D1 RNAi immediately after TBI rescues transcriptional activation of NRF1 and recovers mitochondrial mass after TBI.