BackgroundGenome-wide association studies have identified BIN1 within the second most significant susceptibility locus in late-onset Alzheimer’s disease (AD). BIN1 undergoes complex alternative splicing to generate multiple isoforms with diverse functions in multiple cellular processes including endocytosis and membrane remodeling. An increase in BIN1 expression in AD and an interaction between BIN1 and Tau have been reported. However, disparate descriptions of BIN1 expression and localization in the brain previously reported in the literature and the lack of clarity on brain BIN1 isoforms present formidable challenges to our understanding of how genetic variants in BIN1 increase the risk for AD.MethodsIn this study, we analyzed BIN1 mRNA and protein levels in human brain samples from individuals with or without AD. In addition, we characterized the BIN1 expression and isoform diversity in human and rodent tissue by immunohistochemistry and immunoblotting using a panel of BIN1 antibodies.ResultsHere, we report on BIN1 isoform diversity in the human brain and document alterations in the levels of select BIN1 isoforms in individuals with AD. In addition, we report striking BIN1 localization to white matter tracts in rodent and the human brain, and document that the large majority of BIN1 is expressed in mature oligodendrocytes whereas neuronal BIN1 represents a minor fraction. This predominant non-neuronal BIN1 localization contrasts with the strict neuronal expression and presynaptic localization of the BIN1 paralog, Amphiphysin 1. We also observe upregulation of BIN1 at the onset of postnatal myelination in the brain and during differentiation of cultured oligodendrocytes. Finally, we document that the loss of BIN1 significantly correlates with the extent of demyelination in multiple sclerosis lesions.ConclusionOur study provides new insights into the brain distribution and cellular expression of an important risk factor associated with late-onset AD. We propose that efforts to define how genetic variants in BIN1 elevate the risk for AD would behoove to consider BIN1 function in the context of its main expression in mature oligodendrocytes and the potential for a role of BIN1 in the membrane remodeling that accompanies the process of myelination.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0124-1) contains supplementary material, which is available to authorized users.

Proteolysis of the amyloid precursor protein (APP) liberates various fragments including the proposed initiator of Alzheimer disease-associated dysfunctions, amyloid-␤. However, recent evidence suggests that the accepted view of APP proteolysis by the canonical ␣-, ␤-, and ␥-secretases is simplistic, with the discovery of a number of novel APP secretases (including ␦-and -secretases, alternative ␤-secretases) and additional metabolites, some of which may also cause synaptic dysfunction. Furthermore, various proteins have been identified that interact with APP and modulate its cleavage by the secretases. Here, we give an overview of the increasingly complex picture of APP proteolysis.Currently over 46 million people worldwide are living with dementia (see the Alzheimer's Disease International website) with Alzheimer disease (AD) 3 representing the most common form of dementia. In AD, the amyloid cascade hypothesis posits that amyloid-␤ (A␤), produced through the sequential proteolytic cleavage of the amyloid precursor protein (APP) by the ␤-and ␥-secretases, is a key molecule in initiating and propagating disease pathology including neurofibrillary tangle formation, neuronal cell loss, aberrant synaptic activity, and brain atrophy that lead to the clinically recognized symptoms of dementia (1). However, identification of the A␤ peptide 25 years ago has not yet led to the advent of a viable therapeutic strategy that can slow or halt the progression of AD. Recent studies have revealed new complexities in the proteolytic processing of APP, including the identification of novel secretases which generate APP metabolites that accumulate in the brains of AD patients and may contribute to the synaptic dysfunction observed in the disease. In addition, numerous proteins are being identified that interact with APP, modulating its proteolysis and A␤ production. These new APP secretases and metabolites, along with the APP interactors, may present novel therapeutic targets that are independent of direct modulation of the canonical secretases and that will need to be considered when evaluating the results from current A␤-directed therapies. In this Minireview, we summarize the recent developments in APP proteolysis focusing on the novel secretases, APP interactors, and APP metabolites that are impacting on our understanding of both APP biology and the neurodegenerative disease process. The Canonical ␣-, ␤-, and ␥-Secretases and APP FragmentsThe generally accepted model of APP proteolysis is that APP is processed by one of two distinct proteolytic pathways (Fig. 1A). In the amyloidogenic pathway, ␤-secretase, the ␤-site APP-cleaving enzyme 1 (BACE1), cleaves APP within the ectodomain and liberates a soluble proteolytic fragment, termed soluble APP␤ (sAPP␤), primarily in the endosomal system from the transmembrane APP holoprotein (2). The remaining C-terminal membrane-bound APP fragment, CTF␤, is subsequently cleaved by the presenilin (PS)-containing ␥-secretase multisubunit complex to liberate the A␤ peptide and the APP intrace...

Highlights d The loss of BIN1 in neurons leads to impaired spatial memory consolidation d Neuronal Bin1 cKO mice have deficits in excitatory synaptic transmission d BIN1 regulates presynaptic vesicular release in hippocampal excitatory synapses d The results highlight a non-redundant role for BIN1 in presynaptic regulation

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by pathological brain lesions and a decline in cognitive function. β-Amyloid peptides (Aβ), derived from proteolytic processing of amyloid precursor protein (APP), play a central role in AD pathogenesis. β-Site APP cleaving enzyme 1 (BACE1), the transmembrane aspartyl protease which initiates Aβ production, is axonally transported in neurons and accumulates in dystrophic neurites near cerebral amyloid deposits in AD. BACE1 is modified by S-palmitoylation at four juxtamembrane cysteine residues. S-palmitoylation is a dynamic posttranslational modification that is important for trafficking and function of several synaptic proteins. Here, we investigated the in vivo significance of BACE1 S-palmitoylation through the analysis of knock-in mice with cysteine-to-alanine substitution at the palmitoylated residues (4CA mice). BACE1 expression, as well as processing of APP and other neuronal substrates, was unaltered in 4CA mice despite the lack of BACE1 S-palmitoylation and reduced lipid raft association. Whereas steady-state Aβ levels were similar, synaptic activity-induced endogenous Aβ production was not observed in 4CA mice. Furthermore, we report a significant reduction of cerebral amyloid burden and BACE1 accumulation in dystrophic neurites in the absence of BACE1 S-palmitoylation in mouse models of AD amyloidosis. Studies in cultured neurons suggest that S-palmitoylation is required for dendritic spine localization and axonal targeting of BACE1. Finally, the lack of BACE1 S-palmitoylation mitigates cognitive deficits in 5XFAD mice. Using transgenic mouse models, these results demonstrate that intrinsic posttranslational S-palmitoylation of BACE1 has a significant impact on amyloid pathogenesis and the consequent cognitive decline.

The development of cardiovascular disease is intimately linked to elevated levels of low-density lipoprotein (LDL) cholesterol in the blood. Hepatic LDL receptor (LDLR) levels regulate the amount of plasma LDL. We identified the secreted zinc metalloproteinase, bone morphogenetic protein 1 (BMP1), as responsible for the cleavage of human LDLR within its extracellular ligand-binding repeats at Gly 171 ↓Asp 172 . The resulting 120 kDa membrane-bound C-terminal fragment (CTF) of LDLR had reduced capacity to bind LDL and when expressed in LDLR null cells had compromised LDL uptake as compared to the full length receptor. Pharmacological inhibition of BMP1 or siRNA-mediated knockdown prevented the generation of the 120 kDa CTF and resulted in an increase in LDL uptake into cells. The 120 kDa CTF was detected in the livers from humans and mice expressing human LDLR. Collectively, these results identify that BMP1 regulates cellular LDL uptake and may provide a target to modulate plasma LDL cholesterol.