ABSTRACT
The degeneration of cholinergic neurons is a prominent feature of Alzheimer's disease (AD). In animal models of injury and aging, nerve growth factor (NGF) enhances cholinergic cell survival and function, contributing to improved memory. In the presence of AD pathology, however, NGF-related therapeutics have yet to fulfill their regenerative potential. We propose that stimulating the TrkA receptor, without p75NTR activation, is key for therapeutic efficacy. Supporting this hypothesis, the selective TrkA agonist D3 rescued neurotrophin signaling in TgCRND8 mice, whereas NGF, interacting with both TrkA and p75NTR, did not. D3, delivered intravenously and noninvasively to the basal forebrain using MRI-guided focused ultrasound (MRIgFUS)-mediated blood-brain barrier (BBB) permeability activated TrkA-related signaling cascades and enhanced cholinergic neurotransmission. Recent clinical trials support the safety and feasibility of MRIgFUS BBB modulation in AD patients. Neuroprotective agents targeting TrkA, combined with MRIgFUS BBB modulation, represent a promising strategy to counter neurodegeneration in AD.
Subject(s)
Alzheimer Disease/metabolism , Choline/metabolism , Cholinergic Agents/administration & dosage , Drug Delivery Systems , Receptor, trkA/agonists , Receptor, trkA/metabolism , Ultrasonic Waves , Alzheimer Disease/drug therapy , Alzheimer Disease/etiology , Animals , Blood-Brain Barrier/drug effects , Blood-Brain Barrier/metabolism , Disease Models, Animal , Mice , Mice, Transgenic , Nerve Growth Factor/metabolism , Signal Transduction/drug effectsABSTRACT
Non-invasive gene delivery across the blood-spinal cord barrier (BSCB) remains a challenge for treatment of spinal cord injury and disease. Here, we demonstrate the use of magnetic resonance image-guided focused ultrasound (MRIgFUS) to mediate non-surgical gene delivery to the spinal cord using self-complementary adeno-associated virus serotype 9 (scAAV9). scAAV9 encoding green fluorescent protein (GFP) was injected intravenously in rats at three dosages: 4 × 10(8), 2 × 10(9) and 7 × 10(9) vector genomes per gram (VG g(-1)). MRIgFUS allowed for transient, targeted permeabilization of the BSCB through the interaction of focused ultrasound (FUS) with systemically injected Definity lipid-shelled microbubbles. Viral delivery at 2 × 10(9) and 7 × 10(9) VG g(-1) leads to robust GFP expression in FUS-targeted regions of the spinal cord. At a dose of 2 × 10(9) VG g(-1), GFP expression was found in 36% of oligodendrocytes, and in 87% of neurons in FUS-treated areas. FUS applications to the spinal cord could address a long-term goal of gene therapy: delivering vectors from the circulation to diseased areas in a non-invasive manner.
Subject(s)
Genetic Therapy , Green Fluorescent Proteins/genetics , Spinal Cord Diseases/therapy , Spinal Cord/metabolism , Animals , Dependovirus , Green Fluorescent Proteins/metabolism , Magnetic Resonance Imaging/methods , Male , Neurons/metabolism , Oligodendroglia , Rats, Wistar , Spinal Cord/immunology , Spinal Cord Diseases/genetics , Ultrasonography/methodsABSTRACT
The amyloid precursor protein (APP) and amyloid-ß (Aß) peptide play central roles in the pathology and etiology of Alzheimer's disease. Amyloid-induced impairments in neurogenesis have been investigated in several transgenic mouse models but the mechanism of action remains to be conclusively demonstrated. The changes in neurogenesis during this transition of increasing Aß levels and plaque formation were investigated in the present study. We found that the proliferation of newborn cell in the dentate gyrus was enhanced prior to elevations in soluble Aß production as well as amyloid deposition in 5-week-old TgCRND8 mice, which are well-established Alzheimer's disease models, compared to non-transgenic (Non-Tg) mice. The number of BrdU-positive cells remained higher in TgCRND8 vs Non-Tg mice for a period of 8weeks. The numbers of BrdU/NeuN-positive cells were not significantly different in TgCRND8 compared to Non-Tg mice. A significant decrease in BrdU/GFAP but not in BrdU/S100ß was found in Tg vs Non-Tg at 6-weeks of age. In addition, a unique observation was made using isolated neuroprogenitor cells from TgCRND8 mice which were found to be less viable in culture and produced substantial amounts of secreted Aß peptides. This suggests that the proliferation of neural progenitors in vivo may be modulated by high levels of APP expression and the resulting Aß generated directly by the progenitor cells. These findings indicate that cell proliferation is increased prior to Aß deposition and that cell viability is decreased in TgCRND8 mice over time.
