Application of gene therapy to treat age-related loss of dopamine D-2 receptor

We have investigated the feasibility of using gene therapy to attenuate the age-related decline in striatal dopamine D-2 receptors (D2R) associated wi th reduced motor control. To this end, we have constructed an adenoviral ve ctor containing the cDNA for the rat D2R. When injected into HeLa and HS24 cells in vitro, the vector induced an abundant message for D2R, as demonstr ated by Northern analysis, and produced a membrane-bound protein capable of binding a D2R ligand, [H-3]spiperone. When injected into rat striatum in v ivo, the vector produced a marked increase in D2R near the site of injectio n, as evidenced by increased [H-3]spiperone binding as well as by another m ore specific ligand, [I-125]iodosulpride. The D2R produced in the striatum were functional, as evidenced by rotational behavior induced by a subcutane ous injection of the dopamine agonist, apomorphine. However, we did not obs erve any significant improvement in motor performance during preliminary ex periments in which aged rats received bilateral striatal injections of the vector. In young rats, vector-induced expression of D2R in striatum was inc reased markedly three to five days after infection, but then declined to ba seline levels by day 21. Loss of expression in aged rats proceeded at a som ewhat lower rate. Because of the loss of expression and lack of significant performance enhancement in aged rats following vector injection into the s triatum, we are now pursuing other strategies. These include functional ass essment of the current vector in D2R null mutant mice as well as constructi on of new vectors that may yield more long-ten expression. Published by Els evier Science Inc.