Chemical Modifications of GFAP in Alexander Disease

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1 Chemical Modifications of GFAP in Alexander Disease Natasha T. Snider Assistant Professor Department of Cell Biology and Physiology University of North Carolina at Chapel Hill Alexander Disease Family Conference Madison, WI August 4, 2018

2 GFAP encodes an intermediate filament (IF) protein Intermediate filaments (IFs) form a structural component of cell: the cytoskeleton The cytoskeleton is a structure that is critical for: scaffolding of smaller organelles inside the cell protection from various forms of stress mechanical support of cells cell division cell migration

3 GFAP forms the IF cytoskeleton of astrocytes Wilhemsson et al. PNAS 2006

4 There are 71 human IF proteins expressed across different tissues and cell types Lens: filensin, phakinin, vimentin Nervous system: neurofilaments, GFAP, nestin Skin: epidermal keratins Hair, hair follicle: hair keratins Lung, Liver, GI tract: simple epithelial keratins Cardiac, skeletal and smooth muscle: desmin Blood vessel and other mesenchyme: vimentin All nucleated cells: lamins Omary MB. J Clin Invest (2009)

5 Intermediate filament structures are highly dynamic Schwartz et al. Methods in Enzymol Leube et al. CSH Perspect Biol. 2017

6 IF gene mutations are associated with >70 human diseases

7 Disease-causing IF gene mutations impair filament dynamics KRT14 mutation (epidermolysis bullosa simplex) KRT8 mutation (liver disease predisposition) Werner et al. Mol Biol Cell Owens et al. J Cell Sci 2004

8 IF protein aggregation is a common pathogenesis mechanism of IF-associated diseases Russell et al. J Cell Sci 2004Herrmann et al. Nat Rev Mol Cell Biol 2007; Mahammad et al. J Clin Invest 2013; Omary et al. J Clin Invest 2009; Mizuno et al. J Neurol Sci 2011; Liem and Messing. J Clin Invest 2009

9 Proposed model for Rosenthal Fiber formation and potential opportunities for pharmacological interventions adapted from Sosunov et al. Acta Neuropathol Commun. 2017

10 Phosphorylation is a type of chemical post-translational modification (PTM) that gives proteins unique properties thermofisher.com

11 Phosphorylation regulates IF structure and dynamics Unmodified amino acids Known modifications on IF proteins that are affected by phosphorylation

12 Mutation in a phosphorylation site on GFAP (Y242D) causes Alexander Disease Mutation from Y to D mimics a permanently phosphorylated state Snider et al. J Biol Chem (2013)

13 Mapping phosphorylation sites on GFAP isolated from unaffected control and AxD brain tissue

14 GFAP isolated from brain tissue of younger AxD patients is highly phosphorylated

15 Phospho-mimetic GFAP mutant S13D promotes fragmentation and aggregation of GFAP WT Ac-VEID-CHO P phosphorylation full length GFAP GFAP fragment C cleavage S13D aggregation

16 The enzyme that fragments mutant GFAP in cells (Caspase 6) is expressed in brain from young AxD patients? pathway in AxD brain from patients <14yo

17 Is phosphorylation of GFAP at S13 important in AxD astrocytes? Neural Progenitor Cells Induced pluripotent Stem Cells Astrocytes Precursors Astrocytes Day Medium Type 0 11 NPM NIM StemFlex ADM AMM Induced pluripotent Stem Cells Day 0 Medium change Medium Type 5 9 3D protocol adopted from Sloan et al. Neuron Neuro basal medium NIM Growth factors 16 Every other day Daily medium change StemFlex Onward differentiation Progenitor differentiation Neural induction EGF and FGF BDNF and N3 Twice a week Brain Organoids Adriana Beltran

18 AxD ipsc-astrocytes express large perinuclear aggregates enriched in phosphorylated GFAP (pser13)

19 Abnormal nuclei in AxD ipsc-astrocytes with large ps13-positive GFAP aggregates GFAP ps13-gfap DAPI

20 CK2 is a kinase that is predicted to phosphorylate GFAP on S13 CK2 is a candidate kinase for GFAP phosphorylation CK2β -regulatory subunit CK2α -catalytic subunit adapted from Venerando A Biochem J, 2014

21 Oligomeric form of the regulatory CK2β subunit is present only in brain tissue from young AxD patients

22 CK2 activity is increased in AxD brain from young patients compared to older patients

23 Blocking CK2 activity reduces GFAP aggregation and improves the morphology of Alexander Disease ipsc-astrocytes Control CK2 Inhibitor

24 Future directions: pharmacological approaches to GFAP aggregation Direct GFAP as potential target of known drugs Discovery of novel GFAP-selective compounds Indirect Post-translational modifications (PTMs) targeting PTM on/off enzymes (e.g. kinases) drug repositioning Nosengo N. Nature 2016

25 ACKNOWLEDGEMENTS Rachel Battaglia Kathryn Trogden Parijat Kabiraj Jasmine Robinson Samed Delic Susan Kim Albee Messing Tracy Hagemann UW-Madison Adriana Beltran Raluca Dumitru UNC Stem Cell Core Rhonda Newman Erik Willems Namritha Ravinder Jason Potter Thermo Fisher Scientific Maryland Brain Bank