Hyo Jung Kang

Co-accumulation of vascular endothelial growth factor with β-amyloid in the brain of patients with Alzheimer’s disease

Alzheimers disease (AD) is accompanied by the progressive deposition of beta-amyloid (Abeta) in both senile plaques and cerebral blood vessels, loss of central neurons, and vessel damage. Cerebral hypoperfusion is one of the major clinical features in AD and likely plays a critical role in its pathogenesis. In addition to its major roles in angiogenesis, vascular endothelial growth factor (VEGF) has neurotrophic and neuroprotective effects. VEGF is an ischemia-inducible factor and increased expression of VEGF often occurs in AD. Although the presence of VEGF immunoreactivity in the AD brain has been described previously, the direct interaction of VEGF with Abeta has not been established. Here, we show that VEGF is co-localized with Abeta plaques in the brains of patients with AD. In vitro experiments show that VEGF binds to Abeta with high affinity (K(D) approximate to 50 pM). VEGF is co-aggregated with Abeta without any apparent effect on the rate of aggregation, strongly binds to pre-aggregated Abeta, and is very slowly released from the co-aggregated complex. Continuous deposition of VEGF in the amyloid plaques most likely results in deficiency of available VEGF under hypoperfusion and, thus, may contribute to neurodegeneration and vascular dysfunction in the progression of AD.

Ectopic expression of the catalytic subunit of telomerase protects against brain injury resulting from ischemia and NMDA-induced neurotoxicity.

The catalytic subunit of telomerase reverse transcriptase (TERT) protects dividing cells from replicative senescence in vitro. Here, we show that expression of TERT mRNA is induced in the ipsilateral cortical neurons after occlusion of the middle cerebral artery in adult mice. Transgenic mice that overexpress TERT showed significant resistance to ischemic brain injury. Among excitotoxicity, oxidative stress, and apoptosis comprising of routes of ischemic neuronal death, NMDA receptor-mediated excitotoxicity was reduced in forebrain cell cultures overexpressing TERT. NMDA-induced accumulation of cytosolic free Ca2+ ([Ca2+]c) was reduced in forebrain neurons from TERT transgenic mice, which was attributable to the rapid flow of [Ca2+]c into the mitochondria from the cytosol without change in Ca2+ influx and efflux through the plasma membrane. The present study provides evidence that TERT is inducible in postmitotic neurons after ischemic brain injury and prevents NMDA neurotoxicity through shift of the cytosolic free Ca2+ into the mitochondria, and thus plays a protective role in ameliorating ischemic neuronal cell death.

1,2-bis(2-Aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid induces caspase-mediated apoptosis and reactive oxygen species-mediated necrosis in cultured cortical neurons

Sustained alteration in [Ca2+]i triggers neuronal death. We examined morphological and signaling events of Ca2+‐deficiency‐induced neuronal death. Cortical cell cultures exposed to 20 µm 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N′,N′‐tetraacetic acid (BAPTA‐AM), an intracellular calcium chelator, underwent neuronal apoptosis within 12 h that was evident by shriveled cell bodies, aggregated and condensed nuclear chromatin, and disrupted nuclear membrane. Thereafter, surviving neurons revealed typical necrosis, accompanied by swelling of cell body and mitochondria, over 24 h. Both apoptosis and necrosis were prevented by inclusion of 1 µg/mL cycloheximide, a protein synthesis inhibitor. Treatment with BAPTA‐AM induced translocation of Bax into mitochondria within 4 h and release of cytochrome c from mitochondria over 4–12 h. An active fragment of caspase‐3, a downstream mediator of cytochrome c, was observed within 8 h and cleaved PHF‐1‐positive tau. Administration of zVAD‐fmk, a broad inhibitor of caspases, or DEVD‐amc, a selective inhibitor of caspase‐3, selectively prevented the apoptosis component of BAPTA‐AM neurotoxicity. In contrast, BAPTA‐AM‐induced necrosis was propagated through sequential production of superoxide, mitochondrial and cytoplasmic reactive oxygen species. Combined treatment with caspase inhibitors and antioxidants blocked BAPTA‐AM neurotoxicity. The present study suggests that neurons deficient in [Ca2+]i undergo caspase‐3‐mediated apoptosis and reactive oxygen species (ROS)‐mediated necrosis.

5-Hydroxytryptamine attenuates free radical injury in primary mouse cortical cultures.

The effects of 5-hydroxytryptamine (5-HT) on several types of neuronal injury in mouse cortical cell cultures were tested. Co-treatment with 5-HT prevented free radical-mediated neuronal necrosis induced by FeCl2 or buthionine sulfoximine (BSO) in a dose-dependent manner. Subtype antagonists did not reverse the protective effect and 5-HT showed direct free radical scavenging activity evidenced by its ability to reduce the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) in a cell-free system. Excitotoxic necrosis induced by NMDA or apoptosis induced by staurosporine was not sensitive to 5-HT treatment. These features raise the possibility that the endogenous neurotransmitter 5-HT may work as an innate antioxidant defense mechanism in the CNS.