Delayed secondary biochemical and cellular changes after traumatic brain injury continue for months to years, and are associated with chronic neuroinflammation and progressive neurodegeneration. Physical activity can reduce inflammation and facilitate recovery after brain injury. Here, we investigated the time-dependent effects, and underlying mechanisms of post-traumatic exercise initiation on outcome after moderate traumatic brain injury using a well-characterized mouse controlled cortical impact model. Late exercise initiation beginning at 5 weeks after trauma, but not early initiation of exercise at 1 week, significantly reduced working and retention memory impairment at 3 months, and decreased lesion volume compared to non-exercise injury controls. Cognitive recovery was associated with attenuation of classical inflammatory pathways, activation of alternative inflammatory responses and enhancement of neurogenesis. In contrast, early initiation of exercise failed to alter behavioral recovery or lesion size, while increasing the neurotoxic pro-inflammatory responses. These data underscore the critical importance of timing of exercise initiation after trauma and its relation to neuroinflammation, and challenge the widely held view that effective neuroprotection requires early intervention.

We have reported previously the delayed and differential induction of p38alpha and p38beta mitogen-activated protein kinases (MAPKs) in microglia and astrocytes, respectively, in brain after transient global ischemia. We report here the sustained induction and activation of p38alpha MAPK in activating microglia in rat brain after transient middle cerebral artery occlusion (MCAO). The intraventricular administration of SB203580, a p38 MAPK inhibitor, 30 min before MCAO reduced the infarct volume to 50% of the control, which was accompanied by the significant improvement of neurological deficits. More interestingly, the infarct volume was reduced to 72% and 77% when SB203580 was administered 6 hr and 12 hr after MCAO, respectively. The induction of various factors involved in inflammatory processes, such as inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and cyclooxygenase-2 (COX-2), was suppressed by the administration of SB203580 at 6 hr after MCAO. These results suggest that sustained activation of p38 MAPK pathway and p38 MAPK-associated inflammatory processes play a crucial role in postischemic brain.

We have previously demonstrated that receptors for hematopoietic growth factors, stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF) are expressed in the neurons and the neural progenitor cells (NPCs) in adult rat brain, and systemic administration of SCF and G-CSF in the first week after induction of cortical brain ischemia (3 hrs-7d post-ischemia) significantly improve functional outcome, augment NPC proliferation, and reduce infarct volume in rats. The purpose of the present study was to determine whether SCF and G-CSF pass through the blood brain barrier (BBB) in intact rats. The growth factors were labeled with iodine (I 125 ), a radioactive compound. I 125 -SCF and I 125 -G-CSF were intravenously administered, and the concentrations of I 125 -SCF and I 125 -G-CSF in the blood plasma and the brain were determined at 10, 30, 60, and 120 minutes after injection. We observed that both SCF and G-CSF were slowly and continuously, in the same rate, transported from the blood stream to the brain. In addition, both immunofluorescent staining and western blots showed that receptors for SCF and G-CSF were expressed in the capillaries of adult rat brain, suggesting that SCF and G-CSF entry to the brain may be mediated via receptor-mediated transport, one of the endogenous transports in the BBB. These data indicate that both SCF and G-CSF were able to pass through the BBB in intact animals. This observation will help in further exploring the physiological role of peripheral SCF and G-CSF in the brain and therapeutic possibility to chronic stroke.

HSP70 is a member of the family of heat-shock proteins that are known to be up-regulated in neurons following injury and/ or stress. HSP70 over-expression has been linked to neuroprotection in multiple models, including neurodegenerative disorders. In contrast, less is known about the neuroprotective effects of HSP70 in neuronal apoptosis and with regard to modulation of programmed cell death (PCD) mechanisms in neurons. We examined the effects of HSP70 over-expression by transfection with HSP70-expression plasmids in primary cortical neurons and the SH-SY5Y neuronal cell line using four independent models of apoptosis: etoposide, staurosporine, C2-ceramide, and β-Amyloid. In these apoptotic models, neurons transfected with the HSP70 construct showed significantly reduced induction of nuclear apoptotic markers and/or cell death. Furthermore, we demonstrated that HSP70 binds and potentially inactivates Apoptotic protease-activating factor 1, as well as apoptosis-inducing factor, key molecules involved in development of caspase-dependent and caspase-independent PCD, respectively. Markers of caspase-dependent PCD, including active caspase-3, caspase-9, and cleaved PARP were attenuated in neurons over-expressing HSP70. These data indicate that HSP70 protects against neuronal apoptosis and suggest that these effects reflect, at least in part, to inhibition of both caspase-dependent and caspase-independent PCD pathways.

Neuronal programmed cell death (PCD) contributes to delayed tissue damage after traumatic brain injury (TBI). Both caspase-dependent and caspase-independent mechanisms have been implicated, with the latter including apoptosis inducing factor (AIF). The peptidyl-proplyl isomerase Cyclophilin A (CypA) transports AIF from the cytosol to the nucleus, a key step for AIF-dependent cell death. We compared the effects of single versus combined inhibition of caspase and AIF pathways in a mouse controlled cortical impact (CCI) model, by examining the effects of CypA gene knockout (CypA−/−), caspase inhibition with a pan-caspase inhibitor (boc-aspartyl(OMe)-fluoromethylketone, BAF), or combined modulation. TBI caused caspase activation as well as translocation of AIF to the nucleus. Markers of caspase activation including caspase-specific fodrin cleavage fragments and number of FLIVO positive cells were reduced in BAF-treated CypA+/+ mice, whereas markers of AIF activation including AIF/H2AX interaction and AIF translocation to the nucleus were attenuated in CypA−/− mice. Each single intervention, (CypA−/− or BAF-treated CypA+/+) reduced the number of apoptotic cells (TUNEL-positive) in the cortex and improved long-term sensorimotor function; CypA−/− also attenuated microglial activation after injury. Importantly, BAF-treated CypA−/− mice, showed greater effects than either intervention alone on multiple outcomes including: reduction in TUNEL-positive cells, decrease in neuroinflammation, improved motor and cognitive recovery, and attenuation of lesion volume and neuronal loss in the hippocampus. Using two in vitro neuronal cell death models known to induce AIF-mediated PCD, we also showed that neurons from CypA−/− animals were protected and that effects were unrelated to caspase activation. These data indicate that AIF-mediated and caspase-dependent pathways contribute independently and in parallel to secondary injury after TBI, and suggest that combined therapeutic strategies directed at multiple PCD pathways may provide superior neuroprotection than those directed at single mechanisms.