Project Grant R03AG083702

QUANTIFYING MYELIN DEGENERATION IN AD - PROJECT SUMMARY/ABSTRACT MYELIN IS THE INSULATING SHEATH AROUND NEURONAL AXONS (CONSISTING OF 25% PROTEINS/75% LIPIDS) THAT FACILITATES FAST AND EFFICIENT SIGNAL TRANSDUCTION. IN THE RECENT YEARS, ITS PLASTICITY HAS BEEN SHOWN TO BE KEY FOR COGNITION, MEMORY FORMATION AND CONSOLIDATION. ALZHEIMER'S DISEASE (AD) DEBILITATES COGNITION AND MEMORY, WITH AMYLOID AND TAU BEING HALLMARKS OF THE DISEASE, YET ITS ONSET AND PROGRESSION MECHANISMS REMAIN UNRESOLVED. RECENT EVIDENCE FROM IMAGING, PROTEOMICS, AND GENOMICS SUPPORT MYELIN'S INVOLVEMENT IN AD, AS WELL AS INTERACTIONS WITH AMYLOID, TAU, AND NEUROINFLAMMATION. YET MYELIN'S ROLE, PATTERN OF DEGENERATION, AND INTERPLAY WITH AD PA- THOLOGY REMAIN UNKNOWN. A LIMITING FACTOR HAS BEEN THE LACK OF MYELIN STUDIES INTEGRATING DIFFERENT SCALES: A MA- CROSCOPIC MYELIN IMAGING METHOD WITH TARGETED MOLECULAR PROFILING AND CORRELATIONS WITH KNOWN AD PATHOLOGIES. WE AIM TO ADDRESS THIS IMPORTANT KNOWLEDGE GAP BY COMBINING THREE INNOVATIVE APPROACHES. FIRST, OUR NOVEL SYNCHROTRON X-RAY IMAGING (SAXS-TT) THAT IS SPECIFIC TO MYELIN DUE TO PHOTONS DIFFRACTING OFF THE PERIODIC MYELIN SHEATH AND PROVIDES QUANTITATIVE 3D MAPS OF MYELIN LEVELS AND INTEGRITY. SECOND, OUR DETAILED 3D IMAG- ING-HISTOLOGY REGISTRATION PIPELINE, WHICH ENABLES PRECISE REGISTRATION OF HISTOLOGY TO 3D IMAGES. THIRD, THE USE OF LIPIDOMICS AND PROTEOMICS TO OBTAIN MOLECULAR PROFILING OF AD TISSUE AS WELL AS EXOSOMES -NANOSIZED VESI- CLES RICH IN CARGO (LIPIDS, PROTEINS, RNA) THAT PROVIDE A SNAPSHOT OF CELL PROCESSES AND CELL COMMUNICATION. THE PROJECT AIMS ARE: (1) TO QUANTIFY AD-SPECIFIC MYELIN DEGENERATION IN HIPPOCAMPAL SUBFIELDS AND TRACTS. WE WILL SAXS-TT-SCAN LOW AD, HIGH AD, AND NORMAL AGING HIPPOCAMPAL SPECIMENS, SEGMENT THEIR SUBFIELDS AND TRACTS IN DETAIL, AND TEST IF VULNERABLE TRACTS AND ASSOCIATED SUBFIELDS SUCH AS THE PERFORANT PATHWAY, ENTO- RHINAL CORTEX, DENTATE GYRUS, CA1, CA3 HAVE AD-SPECIFIC MYELINATION. (2) TO DETERMINE THE SPATIAL RELATIONSHIP BETWEEN MYELIN DEGENERATION AND AMYLOID, TAU, OR INFLAMMATION. WE WILL SECTION AIM 1 SPECIMENS, STAIN FOR AMYLOID, TAU, AND MICROGLIA AND REGISTER HISTOLOGY WITH IMAGING USING OUR SERIAL BLOCKFACE PIPELINE. THIS WILL AL- LOW CORRELATING MYELIN WITH STAINS AND PROVIDE EVIDENCE TOWARDS TWO LITERATURE-SUPPORTED HYPOTHESES: THAT MYE- LIN DEGENERATION OVERWHELMS MICROGLIA INHIBITING AMYLOID CLEARANCE, OR THAT TAU PROPAGATES VIA DEMYELINATING TRACTS. (3) TO DETECT AD-SPECIFIC MOLECULAR/EXOSOMAL MARKERS LINKED TO MACROSCOPIC MYELIN DEGENERATION. LIPID DYSREGULATION IS EXTENSIVE IN AD, BUT ITS ORIGIN IS NOT KNOWN. WE WILL TEST IF IT IS DRIVEN BY LIPID-RICH MYELIN, BY COMBINING MYELIN LEVELS WITH LIPIDOMICS/PROTEOMICS ANALYSIS TO QUANTIFY MYELIN LIPIDS AND PROTEINS IN TISSUE AND EXOSOMES, AND TEST IF SPECIFIC LIPIDS AND PROTEINS PARALLEL MACROSCOPIC MYELIN LOSS. INTRODUCING AD EXOSOMES TO OLIGODENDROCYTE CULTURES AND PERFORMING LIPIDOMICS/PROTEOMICS ON THE CELLS CAN SHOW IF IN VIVO MYELIN CHANGES ARE REFLECTED IN VITRO, SUGGESTING A POTENTIAL DISEASE PROPAGATION MECHANISM. THIS STUDY WILL COMBINE MACROSCOPIC WITH MOLECULAR ANALYSES TO PROVIDE A MULTI-FACETED VIEW OF MYELIN PATHOLOGY IN AD.