Use of a Neurotrophic Factor Mimetic to Block Amyloid Toxicity in Alzheimer's Disease Models

Rawal, Devika

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Use of a Neurotrophic Factor Mimetic to Block Amyloid Toxicity in Alzheimer's Disease Models

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Alzheimerâ€™s disease (AD) is the most prevalent neurodegenerative disease in the world. The most accepted hypothesis for the cause of this disease is the amyloid cascade hypothesis, which postulates that the formation of extracellular neurotoxic amyloid-beta binds specific receptors on the surface of neuronal and glial cells to increase cell stress leading to cell death. Our laboratory previously showed that treatment of cultured human SHSY neuronal cells with amyloid beta increases the cellular levels of two key components (caspases-2 and -3) of the extrinsic apoptotic pathway, leading to cell death. The amyloid beta induced caspase elevation was blocked by simultaneously treating the cells with a short mimetic of human ependymin neurotrophic factor, hEPN-1, and the hEPN-1 treatment also blocked cell death. This thesis extends the AD investigation to show that treatment of SHSY cells with amyloid beta may also activate an intrinsic apoptotic mitochondrial stress pathway (assaying caspase-9 as a marker enzyme), and that hEPN-1 treatment significantly lowers this activation. In addition, our laboratory previously showed that treating SHSY cells with amyloid beta increases TUNEL staining, an assay for DNA fragmentation (a hallmark of end stage of apoptosis, and a different apoptotic marker than caspase activation). Treatment with hEPN-1 simultaneously with the amyloid beta, or 6 hrs post amyloid beta, significantly lowered the amyloid beta induced TUNEL signal. This thesis extended the earlier TUNEL experiments to show that hEPN-1 treatment can significantly lower the amyloid beta induced TUNEL staining even when added 18 hrs post amyloid beta. With respect to caspase-8, an initiator caspase in the extrinsic pathway, immunoblot assays of brain lysates from 8 month old transgenic AD mice showed that a 2 week oral delivery of hEPN-1 (conjugated to a carrier to deliver it across the blood brain barrier) significantly lowered caspase-8 levels. Finally, an assay of cellular inhibitors of apoptosis (cIAP) showed a significant increase in their cellular levels in SHSY cells, and in transgenic AD mice treated with hEPN-1, showing for the first time that hEPN-1 may aid cell survival by upregulating proteins known to directly bind specific caspases to block their activity leading to their degradation. The cIAP upregulation occurred in the presence or absence of amyloid beta, indicating that hEPN-1 likely does not block cell death by directly interfering with the interaction of amyloid beta with its cell surface receptors, but instead hEPN-1 may activate an independent cell survival signal transduction pathway in neuronal cells.

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