👤 Sarah Tschirner

The β-secretase BACE1 (β-site amyloid precursor (APP) cleaving enzyme 1) is a major drug target for Alzheimer's disease (AD), as it catalyzes the first step in amyloid β (Aβ) generation, but has additional substrates and functions, in particular in the brain. Several advanced clinical trials with BACE1 inhibitors were stopped because of an adverse event, a mild cognitive worsening. The underlying mechanism is not yet known but may result from co-inhibition of the BACE1-homolog BACE2. While a cerebrospinal fluid (CSF) biomarker for measuring BACE2 activity is not yet established, VCAM-1 has been suggested as such a biomarker, but has not yet been tested upon prolonged dosing in vivo. Using CSF pharmacoproteomics and a subchronic dosing paradigm in non-human primates, we demonstrate that compound 89, a BACE inhibitor not yet tested in humans, and the clinically tested drug elenbecestat inhibit BACE1 in vivo, with little or no effect on BACE2, as seen with a reduction of substrates of BACE1, but not of the BACE2 substrate VCAM-1. As a control, verubecestat, which inhibits both BACE2 and BACE1, reduced CSF abundance of BACE1 substrates as well as of VCAM-1. This study demonstrates the suitability of VCAM-1 as a pharmacodynamic biomarker for measuring BACE2 target engagement in CSF. Show less

The β-secretase BACE1 has become a prime target in Alzheimer's disease (AD) therapy, because it drives the production of pathogenic amyloid β peptides. However, clinical trials with BACE1-targeting drugs were halted due to adverse effects on cognitive performance. We propose here that cognitive impairment by BACE1 inhibitors may be a corollary of a higher function of BACE1 related to proper sleep regulation. To address non-enzymatic effects of BACE1 on ion channels likely involved in the sleep-wake cycle, we analyze sleep patterns in both BACE1-KO mice and a newly generated transgenic line expressing a proteolysis-deficient BACE1 variant (BACE1-KI). We find that BACE1-KI and BACE1-KO mice display common and distinct sleep-wake disturbances. Compared with their respective wild-type littermates, both mutant lines sleep less during the light phase (when they preferentially rest). Furthermore, transition rates between wake and sleep states are altered, as are sleep spindles and EEG power spectra mainly in the gamma range. Thus, a better understanding of how BACE1 interferes with sleep-modulated behaviors is needed if clinical trials with BACE1-targeted inhibitors are to resume. Show less

The β-secretase β-site APP cleaving enzyme 1 (BACE1) is a major drug target for Alzheimer's disease (AD). Clinically tested BACE1 inhibitors induced unexpected cognitive side effects that may stem from their cross-inhibition of the homologous protease BACE2. Yet, little is known about BACE2 functions and substrates in vivo, and no biomarker is available to monitor the extent of BACE2 inhibition in vivo, particularly in cerebrospinal fluid (CSF). To identify a potential CSF biomarker for monitoring BACE2 activity, we analyzed the CSF proteome changes in non-human primates after treatment with a BACE1-selective inhibitor (a brain-targeted monoclonal antibody) in comparison to verubecestat, a clinically tested small-molecule drug inhibiting both BACE1 and BACE2. Acute treatment with either the antibody or verubecestat similarly reduced CSF abundance of the cleavage products of several known BACE1 substrates, including SEZ6, gp130, and CACHD1, demonstrating similar target engagement in vivo. One CSF protein, vascular cell adhesion protein 1 (VCAM-1), was only reduced upon inhibition with verubecestat, but not upon BACE1-selective inhibition with the antibody. We conclude that VCAM-1 is a promising biomarker candidate for monitoring BACE2 inhibition in CSF, which is instrumental for the development of BACE1-selective inhibitors for the prevention of AD. Show less

The β-secretase β-site APP cleaving enzyme (BACE1) is a central drug target for Alzheimer's disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet little is known about physiological BACE2 substrates and functions in vivo. Here, we identify BACE2 as the protease shedding the lymphangiogenic vascular endothelial growth factor receptor 3 (VEGFR3). Inactivation of BACE2, but not BACE1, inhibited shedding of VEGFR3 from primary human lymphatic endothelial cells (LECs) and reduced release of the shed, soluble VEGFR3 (sVEGFR3) ectodomain into the blood of mice, nonhuman primates, and humans. Functionally, BACE2 inactivation increased full-length VEGFR3 and enhanced VEGFR3 signaling in LECs and also in vivo in zebrafish, where enhanced migration of LECs was observed. Thus, this study identifies BACE2 as a modulator of lymphangiogenic VEGFR3 signaling and demonstrates the utility of sVEGFR3 as a pharmacodynamic plasma marker for BACE2 activity in vivo, a prerequisite for developing BACE1-selective inhibitors for safer prevention of Alzheimer's disease. Show less

Loss-of-function mutations in CLN3 cause juvenile Batten disease, featuring neurodegeneration and early-stage neuroinflammation. How loss of CLN3 function leads to early neuroinflammation is not yet understood. Here, we have comprehensively studied microglia from Cln3 Show less