Establishment of Clonal Cell Lines for the Study of Neural Function and Dysfunction

Abstract

The use of gene transfer as a therapeutic approach to diseases of the nervous system depends on the assumption that neurological and psychiatric disorders are a result of defective gene expression and can be corrected by application of modern molecular approaches. The ultimate success of this strategy requires a detailed understanding of normal gene expression in the nervous system. In the case of Parkinson’s disease (Fig. 1b), the primary therapeutic approach has been to either replace the dopamine pharmacologically (i.e., L-DOPA; Pletscher 1990), or to graft fetal dopaminergic neurons (Lindvall 1991). In the case of experimental Parkinsonism, genetically engineered cells have been grafted that synthesize and release dopamine (Gage et al. 1991). While this strategy may be effective for palliative purposes, it does not address the etiological and pathogenetic factors that actually initiate the degenerative process. In fact, it is quite possible that the grafted cells themselves could succumb to the basic disease process. In neurological disorders such as Alzheimer’s disease (AD; Fig. 1a), a variety of neural pathways are selectively vulnerable and not all of the neurotransmitter deficits responsible for the devastating cognitive loss are understood (Saper et al. 1987; Katzman and Saitoh 1991; Decker and McGaugh 1991). For these reasons, “neurotransmitter” replacement strategies may not be as straightforward or efficacious as in the case of Parkinson’s disease. While nerve growth factor (NGF) administration is being considered as a therapy to prevent cholinergic degeneration in AD (Phelps et al. 1989; Marx 1990), the fact that related substances, the neurotrophins (Maisonpierre et al. 1990), have recently been identified, and that other trophic factors may be involved in cholinergic neuronal viability, suggests that sucessful trophic therapy in AD may be complex (Barde 1989; Hefti et al. 1989). Since little information is available regarding putative trophic factors in the non-cholinergic pathways that are affected in AD, additional information regarding this disease process will be necessary before gene transfer or pharmacological approaches can be devised that are likely to be of much use. It is therefore evident that a major challenge to understanding and treating such diseases, either by pharmacologic or genetic approaches, is to determine the molecular mechanisms that mediate formation and maintenance of specific neural pathways (Purves 1988) and the processes that lead to dysfunction. With regard to pharmacologic approaches it is frequently the case that a particular drug may be efficacious because of its broad range of pharmacological effects rather than the exact mode of action which is presumed to be responsible for its therapeutic value. In the case of gene therapy, however, it is apparent that a successful result will depend heavily on a thorough understanding of the detailed pathophysiology of any particular disease process. This type of analysis in brain is made exceedingly difficult by the extensive heterogeneity of cell types and connections that may be affected even within a specific brain region or projection.