Lissencephaly, an autosomal dominant brain malformation caused by mutations in the LIS1 gene, was the first neurological disorder linked directly to cytoplasmic dynein function. This discovery led the way for molecular dissection of events regulating development of the mammalian cerebral cortex. Lis1 and a binding partner, Nudel, bind directly to dynein and regulate its activity. This interaction has been studied almost exclusively in the context of brain development. More recently, gene products associated with later-onset disorders such as schizophrenia, amyotrophic lateral sclerosis (ALS), Perry Syndrome, and Huntington's disease (HD) have been shown to interact directly with dynein pathways. The discovery of an important role for Lis1 and Nudel in regulating dynein-dependent axonal transport in cultured adult rat sensory neurons has led to the hypothesis that perturbing this regulatory network will cause neuronal dysfunction in mice. To test this, the pathological consequences of disrupting Lis1 in post-developmentally will be determined using floxed-Lis1 and Cre strains. Histological, biochemical, and behavioral studies will be carried out to determine if depletion of Lis1 post- developmentally causes neurological dysfunction. Because this could exacerbate disease symptoms in lissencephaly and other neurological disorders, these studies may provide a feasible target for clinical intervention by drugs. Possible candidates are the PPAR3 agonists Avandia and Actos, insulin sensitizers normally used to treat type 2 diabetes. Recent studies indicate that these drugs stimulate dynein in several cell lines. This is blocked by mutations in APC, a microtubule plus end associated protein typically linked to colon cancer. APC has also been found to have critical roles in neurons, influencing both synaptic function and axonal transport. Notably, the dynein response to PPAR3 agonists requires PI3K activity and is mimicked by lithium, a potent Gsk32 inhibitor used to treat mood disorders. Moreover, dynein is a target of Gsk32 in vitro and its phosphorylation results in a 5-fold increase in coimmunoprecipitation of an APC fragment suggesting that inhibition of the kinase could impact dynein interactions. Dynein distribution in sensory neurons is altered in response to PPAR3 agonists, leading to the hypothesis that PPAR3 pathways contribute to regulation of dynein-dependent axonal transport in adult neurons. This will be tested by determining the effect of pharmacological and genetic manipulation of PPAR3/Gsk32/APC pathways on organelle transport in adult rat DRG neurons and determining if crosstalk occurs between Lis1 and PPAR3 pathways.
We have proposed a discreet set of experiments to test specific hypotheses concerning mechanisms regulating the transport of cellular components in adult nerves. The work will likely reveal interactions that, when disrupted, contribute to nervous system disorders. Understanding these mechanisms will be key to design of therapeutic regimes to treat these disorders, and may explain unexpected neurological side effects when drugs go to trial.
