The potential of RNA interference is exciting, offering the possibility of shutting down expression of specific proteins—perhaps in specific cells—for both investigative and therapeutic purposes (see ARF live discussion on this subject). But potential is one thing; delivering on it, quite another. Doing so will likely require many incremental successes, such as the one reported in the November 23 online Nature Medicine by Ralph DiLeone and colleagues at the University of Texas Southwestern Medical Center in Dallas.
DiLeone and colleagues provide in-vivo evidence that one can use RNAi to knock down the expression of a brain enzyme, creating a possible Parkinson’s disease model in the process. Working in mice, the researchers used an adeno-associated virus (AAV) vector to deliver short hairpin (sh) RNA matching a sequence of the RNA for tyrosine hydroxylase, an enzyme critical to dopamine synthesis. The vector was injected unilaterally into the substantia nigra (SN), with a control vector injected into the contralateral SN. Beginning 12 days later, the researchers noted significant reductions in tyrosine hydroxylase in the SN injected with interfering RNA. This reduction was detectable even 50 days after the injections. Accompanying the tyrosine hydroxylase reductions, the researchers found several behavioral deficits, including motor performance (rotarod) deficit and a reduced locomotor response to an amphetamine challenge.
As the authors point out, technologies such as microarrays are going to be dropping countless candidate genes and proteins into the laps of scientists in the near future. Working out the in-vivo roles of these molecules will be very slow if transgenic mice are the only models available. “With AAV vectors, genetic disease models could be rapidly created in many species, including rodents and primates,” write the authors.—Hakon Heimer
- Hommel JD, Sears RM, Georgescu D, Simmons DL, Dileone RJ. Local gene knockdown in the brain using viral-mediated RNA interference. Nat Med. 2003 Dec;9(12):1539-44. PubMed.