The Role of Protein Kinase D2 in Ischemic Stroke

Ischemic stroke, constituting 80–90% of all strokes, is a leading cause of death and long-term disability in adults. There is an urgent need to discover new targets and therapies for this devastating condition. Protein kinase D (PKD), as a key target of diacylglycerol involved in ischemic responses, has not been well studied in ischemic stroke, particularly PKD2. In this study, we found that PKD2 expression and activity were significantly upregulated in the ipsilateral side of the brain after transient focal cerebral ischemia, which coincides with the upregulation of PKD2 in primary neurons in response to in vitro ischemia, implying a potential role of PKD2 in neuronal survival in ischemic stroke. Using kinase-dead PKD2 knock-in (PKD2-KI) mice, we examined whether loss of PKD2 activity affected stroke outcomes in mice subjected to 1 h of transient middle cerebral artery occlusion (tMCAO) and 24 h of reperfusion. Our data demonstrated that PKD2-KI mice exhibited larger infarction volumes and worsened neurological scores, indicative of increased brain injury, as compared to the wild-type (WT) mice, confirming a neuroprotective role of PKD2 in ischemia/reperfusion (I/R) injury. Mouse primary neurons obtained from PKD2-KI mice also exhibited increased cell death as compared to the WT neurons when subjected to in vitro ischemia. We have further identified AKT and CREB as two main signaling nodes through which PKD2 regulates neuronal survival during I/R injury. To determine the therapeutic potential of targeting PKD2 in ischemic stroke, we designed and evaluated PKD2-activating tat-peptides to determine whether targeted activation of PKD2 promotes neuronal survival and functional recovery. D2tatAD peptide specifically, increased neuronal viability and proliferation during I/R injury and reduced infarction size in mice after tMCAO along with increased activation of PKD and downstream AKT and CREB in line with the activation of the PKD2 neuroprotective pathway. Overall, our study demonstrated that PKD2 conferred neuroprotection in ischemic stroke by promoting AKT and CREB activation and targeted activation of PKD by a tat-peptide D2tatAD promoted neuronal survival in response to I/R injury in vitro and in vivo. Our findings highlight the therapeutic potential of targeting PKD for treatment of ischemic stroke where new therapies are in high demand.