Nerve growth factor gene therapy in Alzheimer disease

Nervous system growth factors potently stimulate cell function and prevent neuronal death. These broad effects on survival and function arise from direct downstream activation of antiapoptotic pathways, inhibition of proapoptotic pathways, and stimulation of functionally important cellular mechanisms including ERK/MAP kinase and CREB. Thus, as a class, growth factors offer the potential to treat neurodegenerative disorders for the first time by preventing neuronal degeneration rather than compensating for cell loss after it has occurred. Different growth factors affect distinct and specific populations of neurons: the first nervous system growth factor identified, nerve growth factor, potentially stimulates the survival and function of basal forebrain cholinergic neurons, suggesting that nerve growth factor could be a means for reducing the cholinergic component of cell degeneration in Alzheimer disease. This review will discuss the transition of growth factors from preclinical studies to human clinical trials in Alzheimer disease. The implementation of clinical testing of growth factor therapy for neurologic disease has been constrained by the dual need to achieve adequate concentrations of these proteins in specific brain regions containing degenerating neurons, and preventing growth factor spread to nontargeted regions to avoid adverse effects. Gene therapy is one of a limited number of potential methods for achieving these requirements.