Investigator: Gabriella Papale, Salve Regina University
Mentor: William Van Nostrand, University of Rhode Island
Theme: Neuroscience
Title: StarD5: A novel target in the progression of Alzheimer’s disease 
Award: Early Career Development (2022-2024)

Abstract: Alzheimer’s disease (AD) is a degenerative brain disorder and the main cause of dementia. While it is well understood that accumulation of beta-amyloid (Aβ) plaques and abnormal tau protein (“tau tangles”) are associated with the neurological degeneration of AD, the molecular mechanisms that occur early in the
progression of the disease remain somewhat elusive. It was recently reported that a single nucleotide polymorphism (SNP) in the promoter region of the gene encoding StarD6 may be correlated with AD risk. It is hypothesized that StarD6 plays a neuroprotective role, most likely by binding and delivering neurosteroids
to their site of action. Understanding these interactions is crucial in revealing the role of StarD6 in vivo, in both homeostatic conditions and neurodegenerative disorders such as Alzheimer’s Disease.

Aim 1: To fully characterize the ligand-binding site of StarD6. Several amino acid residues in the binding cavity of StarD6 have suggested involvement in ligand binding, most likely through the formation of hydrogen bonds. However, no further characterization of these residues has been completed to date. It is hypothesized that the inherent redundancy of hydrogen-bonding capable amino acid residues in the StarD6 binding cavity contribute to the heterogeneity of StarD6 ligands. Molecular dynamics simulations in coordination with site-directed mutagenesis and fluorescent-based binding and activity assays will be used to fully characterize the interactions between each of the implicated amino acid residues and both known
and putative StarD6 ligands.

Aim 2: To investigate the importance of post-translational modifications on StarD6. StarD6 is predicted to have a molecular weight of approximately 25 kDa but is often observed at a slightly higher molecular weight in murine tissues using gel electrophoresis and Western blot analysis. This discrepancy was suggested to be due to post-translational modification (PTM), but no confirmatory studies have been
performed. It is hypothesized that PTMs such as phosphorylation and acetylation modulate the ability of StarD6 to bind steroid compounds and deliver them to lipid bilayers such as the outer mitochondrial membrane. Phosphorylation and acetylation of StarD6 will be detected using a cell-based expression system
and a combination of immunoprecipitation, Western blot analysis, and tandem mass spectrometry (MS/MS). Effects of these PTMs on binding affinity will be tested using site-directed mutagenesis in conjunction with
fluorescence-based binding and activity assays.

Relevance: Alzheimer’s Disease (AD) is a degenerative brain disorder that affects over six million Americans, and this number is expected to double by 2050 unless research reveals a new treatment or cure. Recent genetic studies have linked the protein StarD6 to risk of AD, but little is known regarding the natural role of this protein in the brain and other tissues. This study will investigate structural and functional aspects of StarD6, positioning this protein as a novel and exciting target in the fight against AD.