Laura Jenelle Blair - US grants

The microtubule-associated protein tau is now thought to contribute to disease progression and pathogenesis in Alzheimer's disease both from within neurons and even between neurons via prion-like propagation. However, mechanisms that contribute to these pathogenic processes remain unclear. Here, we will fill these gaps in our knowledge by exploiting known anti-aggregant small chaperones that can function both inside and outside of neurons to distinctly regulate tau assembly and possibly toxicity. In fact, these small heat shock proteins are known to reside in the extracellular space and associate with both tau tangles and amyloid ß (Aß) plaques. We also know that small Hsps increase in the aging brain and even further in the Alzheimer's brain. Our team showed that a small heat shock protein blocks tau aggregation, reduces tau levels in vivo and restores hippocampal function in a tau transgenic mouse model; but a phosphorylated variant that has impaired activity may actually promote toxicity by producing more tau oligomers. We now have evidence that the other small Hsps can also prevent tau aggregation, and even just small peptidic cores of both these small Hsps are capable of blocking tau aggregation. With these tools, we can now test the hypothesis that tau toxicity arises due to structural changes in tau assemblies brought on by small Hsps that can function both inside and outside of the neuron. To test this, we will determine the impact of distinct small Hsp variants on tau oligomer formation and uptake. We will also determine the impact of intracellular small Hsps on functional deficits in a mouse model of tau proteotoxicity. And we will determine the impact of extracellular small Hsps on functional deficits and tau uptake in mouse and human models of tau proteotoxicity. Through these studies, we anticipate that we will identify ways to regulate tau aggregation using small Hsps, which will allow us to home in on structures of toxic tau intermediates. We also will determine whether distinct small Hsp variants can differentially triage aberrant tau from inside and outside of the neuron in the brain, possibly allowing us to improve the specificity of therapeutics targeting this mechanism.

DESCRIPTION (provided by applicant): In this revised application, we will investigate how the FK506 binding protein 5 (FKBP5) is up- regulated to coordinate how the brain responds to stress. Since 2004, our team has worked to show that single nucleotide polymorphisms (SNPs) in the FKBP5 gene associate with increased risk of psychopathologies caused by stress, as highlighted in Nature Genetics 36:1319-25 2004 & JAMA 299:1291-305 2008. We have also shown that these risk SNPs increase the levels of FKBP5 through a mechanism that involves demethylation of the FKBP5 gene (Nature Neuroscience. 16:33-41 2013 & Journal of Clinical Investigation 123:4158-69 2013). There are currently 2 other mechanisms besides these SNPs that are known to increase FKBP5 levels in the brain: 1) Stimulation of the glucocorticoid receptor (GR) by the steroid hormone cortisol (corticosterone/CORT), and 2) modulation of the receptor tyrosine kinase EphB2 (Attwood et al. Nature 473:372-5 2011). In our previous work, we found that mice lacking the FKBP5 gene (FKBP5-/- mice) are protected from stress-induced depressive-like phenotypes, and that apart from this improved resiliency, these mice seem very normal. Acute suppression of FKBP5 in the amygdala has also been shown to protect mice from anxiety-like behavior, but there are still gaps in our knowledge about the function and regulation of FKBP5 in the brain. While we know that FKBP5 does reduce resiliency to stress, we do not know whether chronically increased FKBP5 levels in the brain can fully model impaired stress resiliency through a mechanism that is similar to humans carrying risk SNPs. We also do not know how FKBP5 overexpression impacts learning and memory despite clear connections between stress and cognitive function. We know that chronic stress disrupts cognitive processes and electrophysiological function of neurons. But we do not know if stress- induced deficits in cognition, plasticity, hippocampal volume or neurogenesis are mediated by FKBP5. Lastly, we know that FKBP5 expression is up-regulated by GR and EphB2 signaling, and we also know that demethylation of the FKBP5 gene in humans contributes to FKBP5 upregulation. But we do not know how other epigenetic modifying proteins contribute to FKBP5 expression and demethylation, nor do we know how the EphB2 receptor regulates FKBP5 expression through a similar methylation mechanism. To fill these gaps, we will examine the effects of FKBP5 overexpression on stress resiliency and cognitive function, examine the effects of FKBP5 on cognitive and neuronal deficits caused by chronic stress and investigate the mechanisms that control FKBP5 expression. We anticipate that these studies will show the importance of FKBP5 to the brain's stress response, leading to new insights about its role in psychopathologies and cognitive function. We will also define new upstream regulators of FKBP5 expression.