Project description:Extracellular senile plaques of amyloid beta (Abeta) are a pathological hallmark in brain of patients with Alzheimer`s Disease (AD). Abeta is generated by the amyloidogenic processing of the amyloid precursor protein (APP). Concomitant to Abeta load, AD brain is characterized by an increase in protein level and activity of the angiotensin-converting enzyme (ACE). ACE inhibitors are a widely used class of drugs with established benefits for patients with cardiovascular disease. However, the role of ACE and ACE inhibition in the development of Abeta plaques and the process of AD-related neurodegeneration is not clear since ACE was reported to degrade Abeta. To investigate the effect of ACE inhibition on AD-related pathomechanisms, we used Tg2576 mice with neuron-specific expression of APPSwe as AD model. From 12 months of age, substantial Abeta plaque load accumulates in the hippocampus of Tg2576 mice as a brain region, which is highly vulnerable to AD-related neurodegeneration. The effect of central ACE inhibition was studied by treatment of 12 month-old Tg2576 mice for six months with the brain penetrating ACE inhibitor captopril. At an age of 18 months, hippocampal gene expression profiling was performed of captopril-treated Tg2576 mice relative to untreated 18 month-old Tg2576 controls with high Abeta plaque load. As an additional control, we used 12 month-old Tg2576 mice with low Abeta plaque load. Whole genome microarray gene expression profiling revealed gene expression changes induced by the brain-penetrating ACE inhibitor captopril, which could reflect the neuro-regenerative potential of central ACE inhibition. Microarray gene expression profiling was performed of hippocampi isolated from aged, 18 month-old Tg2576 (APPSwe-transgenic) AD mice with high Abeta plaque load relative to age-matched Tg2576 mice, which were treated for 6 months with the centrally active ACE inhibitor captopril. Another study group consisted of 12 month-old Tg2576 mice with low Abeta plaque load. In total, three study groups were analyzed, i.e. (i) 18 month-old untreated Tg2576 mice with high Abeta plaque load, (ii) age-matched Tg2576 mice treated for 6 months with the brain-penetrating ACE inhibitor captopril (20 mg/kg body weight/day in drinking water), and (iii) untreated 12 month-old Tg2576 mice with low Abeta plaque load reflecting the time point when captopril treatment was initiated. Two biological replicates were made of each group, and total hippocampal RNA of four mice was pooled for one gene chip.

Project description:Many forms of synaptic plasticity are critically dependent upon production of cGMP to trigger activity-dependent increases in synaptic size and strength. Phosphodiesterase 9A (PDE9A) is a high affinity, cGMP-specific phosphodiesterase with widespread distribution in the central nervous system. Inhibition of PDE9A results in significant accumulation of cGMP in brain tissue and cerebrospinal fluid (CSF) of rodents, and increases CSF cGMP in human volunteers. We hypothesized that chronic exposure to a PDE9A inhibitor, and the associated elevations in brain cGMP could provide a therapeutic benefit to vulnerable synapses chronically exposed to Aβ in transgenic mice over-expressing human mutant amyloid precursor protein (Tg2576 mice). A total of N=20 animals per group of 4 month old Tg2576 mice and non-transgenic littermates (WT) were implanted with Alzet osmotic minipumps to deliver vehicle or the PDE9A inhibitor PF-04447943. Neurobehavioral outcomes were measured as conditioned fear response after 28 days of treatment and subsequently brains were harvested for measurement of Aβ, gene expression profiling or synaptic density as assessed by Golgi staining of dendrites. Dendritic spine density on apical dendrites of CA1 neurons exhibited a small but significant deficit in the density of dendritic spines in vehicle treated Tg2576 mice as compared to WT mice. This deficit was ameliorated by 30 days of exposure to PF-04447943. No significant drug effect was observed in WT mice. No significant effects of drug treatment were observed on Aβ levels in Tg2576 mice. Behavioral analysis of Tg2576 mice showed deficits in fear conditioning as early as 2 months old, and therefore were considered unlikely to be due to the accumulation of oligomeric Aβ. These deficits were not affected by drug treatment. Transcriptional profiles of Tg2576 mice treated with drug compared to vehicle showed evidence of regulation of pathways related to synaptic plasticity and remodeling of the dendritic cytoskeleton, consistent with stabilization of vulnerable spine structure. These data supports the hypothesis that PDE9A inhibition can stabilize vulnerable synapses early in the Alzheimer’s disease process. 4-month old Tg2576 mice and non-transgenic (WT) littermates were implanted with minipumps to deliver vehicle or the PDE9A-inhibitor, PF-04447943, for 28 days. At the end of the study, hippocampus and frontal cortex were dissected from n=8 mice per group, RNA was isolated, and hybridized to Affymetrix 430 2.0 mouse whole genome microarray.

Project description:Many forms of synaptic plasticity are critically dependent upon production of cGMP to trigger activity-dependent increases in synaptic size and strength. Phosphodiesterase 9A (PDE9A) is a high affinity, cGMP-specific phosphodiesterase with widespread distribution in the central nervous system. Inhibition of PDE9A results in significant accumulation of cGMP in brain tissue and cerebrospinal fluid (CSF) of rodents, and increases CSF cGMP in human volunteers. We hypothesized that chronic exposure to a PDE9A inhibitor, and the associated elevations in brain cGMP could provide a therapeutic benefit to vulnerable synapses chronically exposed to Aβ in transgenic mice over-expressing human mutant amyloid precursor protein (Tg2576 mice). A total of N=20 animals per group of 4 month old Tg2576 mice and non-transgenic littermates (WT) were implanted with Alzet osmotic minipumps to deliver vehicle or the PDE9A inhibitor PF-04447943. Neurobehavioral outcomes were measured as conditioned fear response after 28 days of treatment and subsequently brains were harvested for measurement of Aβ, gene expression profiling or synaptic density as assessed by Golgi staining of dendrites. Dendritic spine density on apical dendrites of CA1 neurons exhibited a small but significant deficit in the density of dendritic spines in vehicle treated Tg2576 mice as compared to WT mice. This deficit was ameliorated by 30 days of exposure to PF-04447943. No significant drug effect was observed in WT mice. No significant effects of drug treatment were observed on Aβ levels in Tg2576 mice. Behavioral analysis of Tg2576 mice showed deficits in fear conditioning as early as 2 months old, and therefore were considered unlikely to be due to the accumulation of oligomeric Aβ. These deficits were not affected by drug treatment. Transcriptional profiles of Tg2576 mice treated with drug compared to vehicle showed evidence of regulation of pathways related to synaptic plasticity and remodeling of the dendritic cytoskeleton, consistent with stabilization of vulnerable spine structure. These data supports the hypothesis that PDE9A inhibition can stabilize vulnerable synapses early in the Alzheimer’s disease process.

Dataset Information

Mouse Wild Type and APP transgenic (Tg2576) hippocampus and response to LXR Agonist

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