PROJECT SUMMARY / ABSTRACT In the height of the opioid crisis in our country, deaths from methamphetamine (METH) overdose are on the rise, and there is no FDA-approved medication for METH use disorder (MUD). New drug targets are needed, particularly for people who heavily use the drug because they have the most difficulty quitting METH use, suffer from a variety of serious neurological problems, and are at high risk to overdose on the drug. Our work with a rat model of heavy compulsive METH consumption (severe MUD) provided evidence that overexpression of neuroprotective protein parkin in the nucleus accumbens (NAc), a key reward-mediating brain area, plays a role in severe MUD. Parkin is a protein-ubiquitin ligase known to play a critical role in maintaining mitochondrial health and, therefore, in maintaining generation of cellular energy - adenosine triphosphate (ATP). Our preliminary proteomic data shows that upregulation of parkin in the NAc leads to upregulation of several Krebs cycle enzymes whereas parkin knockout leads to their downregulation. Dysfunctional mitochondria are the known consequence of METH use. This proposal investigates the novel hypothesis that parkin decreases METH cravings and addictive behaviors by the Krebs cycle function in the NAc from METH neurotoxicity. This helps to maintain ATP generation in METH-exposed NAc neurons, which otherwise would be impaired by METH- induced oxidative stress. In other words, we will test whether dysfunctional mitochondria are a cause of MUD. We will test the hypothesis by three independent specific aims. The specific aim 1 will establish whether and how parkin protects Krebs cycle function in rat NAc from neurotoxicity of self-administered METH. The specific aim 2 will determine whether parkin overexpression in the NAc of rats with developed severe MUD will decrease METH addictive behaviors. The specific aim 3 will determine whether overexpression of oxidative stress- sensitive Krebs cycle enzyme DLST (dihydrolipoamide S-succinyl-transferase) in the NAc of rats with developed severe MUD will decrease METH addictive behaviors. Given that parkin may serve a dual function of decreasing METH neurotoxicity and METH cravings, these studies will determine whether targeting parkin has a significant therapeutic potential in severe MUD. Given the limited indirect data suggesting that METH neurotoxicity in NAc mitochondria contributes to development of MUD, these studies will provide clarity about the role of METH- induced oxidative stress in mediating METH use and in development of motivation to seek METH during abstinence. Furthermore, the results will benefit opioid and alcohol use disorder research as these disorders induce mitochondrial dysfunction. Lastly, since chronic use of METH, particularly at high doses, predisposes to development of Parkinson’s disease and potentially also to Alzheimer’s disease, the results from this research will add information to these research areas.

PROJECT NARRATIVE The proposed research is aimed to determine whether insufficient energy production caused by an impairment of the Krebs cycle plays a role in methamphetamine use disorder. The project is relevant to the public health because there is no FDA-approved medication for methamphetamine use disorder while illicit use of methamphetamine and deaths from methamphetamine overdose are rising in the United States. Upon successful completion of the project, we will know whether a loss of function by three Krebs cycle enzymes leads to a deficit in neuronal energy in experimental rats with methamphetamine use disorder and whether upregulation of neuroprotective protein parkin can prevent relapse to methamphetamine use.