This application is a competitive renewal for MH18501 now in its 40th year of continuous funding. The grant has supported our research on fundamental neurochemical mechanisms which may underlie the actions of psychotropic drugs. In recent years we have characterized novel neurotransmitters such as nitric oxide and D-serine, areas which we will continue to study in the coming years but which, for want of space, we do not describe in detail in the application. Instead, we focus on three areas of investigation. One involves the small G protein Rhes as a mediator of the neurotoxicity elicited by mutant huntingtin (mHtt). Though mHtt was described as the genetic basis of Huntington's Disease 16 years ago, how it elicited the highly selective damage to the corpus striatum characteristic of HD was unclear, because Htt is uniformed expressed throughout the brain and the rest of the body. We discovered that the striatal-specific protein Rhes binds avidly to mHtt, stimulating its SUMOylation leading to disaggregation and neurotoxicity of mHtt. We propose studies with Rhes knockout mice to elucidate its normal function and will cross-breed these animals with HD mice to evaluate potential alterations of symptoms. Also, we recently discovered that Rhes, like the small G protein Rheb, dramatically stimulates the protein translation activator mTOR, with Rhes knockout mice manifesting an 80% decline in striatal mTOR signaling. The binding of Rhes to mHtt may decrease its accessibility to mTOR with the resultant diminished trophic actions of mTOR accounting for the pronounced shrinkage of the striatum in HD. We propose to elucidate Rhes-mTOR relationships. We also propose to extend our recent findings that hydrogen sulfide (H2S) is physiologically generated by cystathionine-gamma- lyase (CSE) in mammalian peripheral tissues and by cystathionine beta-syntheses (CBS) in the brain. We have discovered that H2S physiologically mediates endothelial derived relaxing factor of blood vessels and regulates blood pressure, as EDRF activity is markedly decreased in CSE knockout mice which are hypertensive. We have also discovered that H2S signals by sulfhydrating proteins. We propose further studies elucidating H2S as a messenger molecule in the brain and the rest of the body. We have recently discovered that IP7 formed by IP6 kinase-1 (IP6K1) is an important physiologic regulator of the Akt/mTOR protein translational pathway. Thus, Akt/mTOR signaling is dramatically augmented in IP6K1 knockout mice due to the very potent inhibition of Akt by IP7. Moreover, IP6K1 knockout mice display insulin hypersensitivity and fail to gain weight on a high fat diet. We propose to characterize how IP6K1 signaling regulates Akt/mTOR utilizing the IP6K1 knockout mice as valuable tools.
Relevance of our research to public health includes the possibility that drugs inhibiting Rhes-mutant huntingtin binding will delay/prevent Huntington Disease brain damage. As a major messenger molecule H2S is worthy of characterization - we already know it is a principal regulator of blood vessels and anticipate other important functions. Akt/mTOR signaling is critical for brain function so that our elucidation of its regulation by inositol pyrophosphates may have therapeutic relevance.
|Mealer, Robert G; Murray, Alexandra J; Shahani, Neelam et al. (2014) Rhes, a striatal-selective protein implicated in Huntington disease, binds beclin-1 and activates autophagy. J Biol Chem 289:3547-54|
|Subramaniam, Srinivasa; Napolitano, Francesco; Mealer, Robert G et al. (2012) Rhes, a striatal-enriched small G protein, mediates mTOR signaling and L-DOPA-induced dyskinesia. Nat Neurosci 15:191-3|
|Mustafa, Asif K; Gadalla, Moataz M; Sen, Nilkantha et al. (2009) H2S signals through protein S-sulfhydration. Sci Signal 2:ra72|