The crystal structure of amyloid precursor-like protein 2 E2 domain completes the amyloid precursor protein family.

The amyloid precursor-like protein 2 (APLP2) molecule is a type I transmembrane protein that is crucial for survival, cell-cell adhesion, neuronal development, myelination, cancer metastasis, modulation of metal, and glucose and insulin homeostasis. Moreover, the importance of the amyloid precursor protein (APP) family in biology and disease is very well known because of its central role in Alzheimer disease. In this study, we determined the crystal structure of the independently folded E2 domain of APLP2 and compared that with its paralogues APP and APLP2, demonstrating high overall structural similarities. The crystal structure of APLP2 E2 was solved as an antiparallel dimer, and analysis of the protein interfaces revealed a distinct mode of dimerization that differs from the previously reported dimerization of either APP or APLP1. Analysis of the APLP2 E2 metal binding sites suggested it binds zinc and copper in a similar manner to APP and APLP1. The structure of this key protein might suggest a relationship between the distinct mode of dimerization and its biologic functions.-Roisman, L. C., Han, S., Chuei, M. J., Connor, A. R., Cappai, R. The crystal structure of amyloid precursor-like protein 2 E2 domain completes the amyloid precursor protein family.

Amyloid precursor protein and amyloid precursor-like protein 2 have distinct roles in modulating myelination, demyelination, and remyelination of axons.

The identification of factors that regulate myelination provides important insight into the molecular mechanisms that coordinate nervous system development and myelin regeneration after injury. In this study, we investigated the role of amyloid precursor protein (APP) and its paralogue amyloid precursor-like protein 2 (APLP2) in myelination using APP and APLP2 knockout (KO) mice. Given that BACE1 regulates myelination and myelin sheath thickness in both the peripheral and central nervous systems, we sought to determine if APP and APLP2, as alternate BACE1 substrates, also modulate myelination, and therefore provide a better understanding of the events regulating axonal myelination. In the peripheral nervous system, we identified that adult, but not juvenile KO mice, have lower densities of myelinated axons in their sciatic nerves while in the central nervous system, axons within both the optic nerves and corpus callosum of both KO mice were significantly hypomyelinated compared to wild-type (WT) controls. Biochemical analysis demonstrated significant increases in BACE1 and myelin oligodendrocyte glycoprotein and decreased NRG1 and proteolipid protein levels in both KO brain tissue. The acute cuprizone model of demyelination/remyelination revealed that whereas axons in the corpus callosum of WT and APLP2-KO mice underwent similar degrees of demyelination and subsequent remyelination, the myelinated callosal axons in APP-KO mice were less susceptible to cuprizone-induced demyelination and showed a failure in remyelination after cuprizone withdrawal. These data identified APP and APLP2 as modulators of normal myelination and demyelination/remyelination conditions. Deletion of APP and APLP2 identifies novel interplays between the BACE1 substrates in the regulation of myelination.

First-in-human clinical trial of allogeneic, platelet-derived extracellular vesicles as a potential therapeutic for delayed wound healing.

The release of growth factors, cytokines and extracellular matrix modifiers by activated platelets is an important step in the process of healthy wound healing. Extracellular vesicles (EVs) released by activated platelets carry this bioactive cargo in an enriched form, and may therefore represent a potential therapeutic for the treatment of delayed wound healing, such as chronic wounds. While EVs show great promise in regenerative medicine, their production at clinical scale remains a critical challenge and their tolerability in humans is still to be fully established. In this work, we demonstrate that Ligand-based Exosome Affinity Purification (LEAP) chromatography can successfully isolate platelet EVs (pEVs) of clinical grade from activated platelets, which retain the regenerative properties of the parent cell. LEAP-isolated pEVs display the expected biophysical features of EV populations and transport essential proteins in wound healing processes, including insulin growth factor (IGF) and transforming growth factor beta (TGF-ß). In vitro studies show that pEVs induce proliferation and migration of dermal fibroblasts and increase dermal endothelial cells' angiogenic potential, demonstrating their wound healing potential. pEV treatment activates the ERK and Akt signalling pathways within recipient cells. In a first-in-human, double-blind, placebo-controlled, phase I clinical trial of healthy volunteer adults, designed primarily to assess safety in the context of wound healing, we demonstrate that injections of LEAP-purified pEVs in formulation buffer are safe and well tolerated (Plexoval II study, ACTRN12620000944932). As a secondary objective, biological activity in the context of wound healing rate was assessed. In this cohort of healthy participants, in which the wound bed would not be expected to be deficient in the bioactive cargo that pEVs carry, all wounds healed rapidly and completely and no difference in time to wound closure of the treated and untreated wounds was observed at the single dose tested. The outcomes of this study evidence that pEVs manufactured through the LEAP process can be injected safely in humans as a potential wound healing treatment, and warrant further study in clinical trials designed expressly to assess therapeutic efficacy in patients with delayed or disrupted wound healing.