A Novel Mouse Model to Study Motoric Aging Induced by Benzodiazepine Abuse

Abstract Benzodiazepines (BZDs) are a widely used class of sedative and anti-anxiety medications, and their usage increases with age (NIH news, 2014). While BZDs are powerfully effective for treating hyper-excitatory disorders, they can have serious side effects, such as motor deficits. The vast majority of elderly BZD users stays in BZD therapy for a prolonged period (NIH news, 2014), which exacerbates the motoric deficits. The adverse effects and long-term use of BZD are seen more in elderly women than other age/gender population groups. However, how chronic BZD (cBZD) usage impairs the motoric function of elderly women remains virtually unknown. The objective for this proposal is to establish a transgenic mouse model that is capable of identifying the mechanism by which cBZD induces motoric aging in female subjects. BZD binds to the GABA- BZD receptor complex, thereby eliciting CNS depressant effects. It is also well known that BZDs including diazepam, lorazepam, and alprazolam, bind to mitochondrial BZD receptors (mBZD-R), located in mitochondrial membranes. The excessive stimulation of mBZD-R damages mitochondrial membranes where mitochondrial respiration takes place, consequently overproducing reactive O2 species (ROS). The binding of BZD to mBZD-R was significantly increased in the cerebellum of the elderly with cognitive disorders (Yasuno et al., 2012), suggesting that mBZD-R plays a role in brain aging. In particular, mBZD-R activity involves pro- apoptotic protein p38 such that a p38 inhibitor attenuates the apoptosis induced by mBZD-R ligands (Sutter et al., 2004). Since ROS activates p38 by phosphorylation, the apoptotic effect of p38 would be more severe in elderly women who lack 17ß-estradiol (E2), which directly scavenges ROS. Purkinje cells are major cerebellar neurons that are particularly vulnerable to apoptotic p38 (see Approach, Guan et al., 2005). Purkinje neurons show an age-dependent accumulation of p38 in a manner that is mitigated by E2 (Jung et al., 2011). We have generated mice that lack p38 in Purkinje neurons, and observed that these mice are more resistant to cBZD- induced motoric deficit and mitochondrial respiratory suppression than wild-type mice. This protective effect of Purkinje p38 downregulation is more prominent in female mice than male mice, suggesting that a female hormone, especially E2, may play a role in that protection. These observations suggest that cBZD provokes an adverse interaction between the mBZD-R and p38 at an E2-deficient age, resulting in Purkinje apoptosis and motoric aging. We will pursue our objective by achieving Specific Aim 1: Determine the mechanism by which cBZD induces motoric aging. We will test a two-step hypothesis: 1A) cBZD's binding to mBZD-R age- dependently suppresses mitochondrial respiration and 1B) cBZD induces Purkinje neuronal apoptosis and motoric deficit through ROS-activated p38 at an E2-deficient age. The proposed research is absolutely critical because it is expected to establish a solid model and foundational mechanism that will be a first step toward lessening the motoric deterioration of elderly women receiving cBZD.