Biology subjects

Munter, L. M.

Publications and source records attributed to Munter, L. M..

6 recordsLinked to original sources

bioRxiv2026

Doublecortin mutation disrupts lattice-dependent proximity to reveal cytoskeletal networks in developing neurons

Doublecortin (DCX) is a microtubule-associated protein (MAP) required for neuronal migration and cortical development. However, DCX is not sufficient to direct these processes on its own. Instead, nucleokinesis, growth cone advancement, collateral branching, and polarity depend on the coordination of different MAPs and cytoskeletal proteins, including DCX, to define distinct polymer properties and cytoskeletal interfaces. While many of these proteins have been investigated for their mechanistic cytoskeletal engagement, the spatiotemporal proteomic landscape of developing neurons remains largely uncharacterized. Here, we explore DCX-centric cytoskeletal networks using BioID accumulated throughout the differentiation of cortical neurons from induced pluripotent stem cells (iPSCs). Using the morphological staging of these cells as temporal landmarks, we generate a time-resolved proteomic atlas that charts DCX's molecular environment throughout differentiation. From this atlas, we identify a cluster of cytoskeletal proteins whose persistent proximity to DCX is disrupted with the disease-associated mutation, DCX p.Arg178Leu (R178L). Consistent with R178L's diminished cooperativity, we find many of these species are implicated in modulating microtubule stability and intracellular transport, including proteins EML4 and MAP7D1. Together, our findings place DCX at the interface of distinct microtubule populations and cytoskeletal systems throughout neuronal development.

developmental biology↗

bioRxiv2024

Reducing CETP activity prevents memory decline in an Alzheimer's disease mouse model

Epidemiological studies have shown that lower activity of the cholesteryl ester transfer protein (CETP) correlates with reduced Alzheimers disease (AD) risk. While small molecule CETP inhibitors like evacetrapib have previously been assessed for cardiovascular diseases, their involvement in AD has not been investigated. Here, we establish CETP as a novel pharmacological target for AD treatment. Using CETP transgenic mice crossed to a mouse model of amyloidosis and administering evacetrapib, we provide evidence that CETP inhibition maintained memory independent of classic AD markers, increased hippocampal cholesterol, altered plasma lipoproteins, and changed transcription of genes linked to brain barriers. Using proteomic data of cerebrospinal fluid from cognitively unimpaired individuals at risk for AD (the PREVENT-AD cohort), we confirm that our mouse model reflects physiological changes in pre-symptomatic human subjects. We propose the repurposing of CETP inhibitors as an effective therapeutic strategy to delay or prevent cognitive impairment in AD.

neuroscience↗

bioRxiv2024

Loss of the APP regulator RHBDL4 preserves memory in an Alzheimer's disease mouse model.

Characteristic cerebral pathological changes of Alzheimers disease (AD) such as glucose hypometabolism or the accumulation of cleavage products of the amyloid precursor protein (APP), known as A{beta} peptides, lead to sustained endoplasmic reticulum (ER) stress and neurodegeneration. To preserve ER homeostasis, cells activate their unfolded protein response (UPR). The rhomboid-like-protease 4 (RHBDL4) is an enzyme that participates in the UPR by targeting proteins for proteasomal degradation. We demonstrated previously that RHBLD4 cleaves APP in HEK293T cells, leading to decreased total APP and A{beta}. More recently, we showed that RHBDL4 processes APP in mouse primary mixed cortical cultures as well. Here, we aim to examine the physiological relevance of RHBDL4 in the brain. We first found that brain samples from AD patients and an AD mouse model (APPtg) showed increased RHBDL4 mRNA and protein expression. To determine the effects of RHBDL4s absence on APP physiology in vivo, we crossed APPtg mice to a RHBDL4 knockout (R4-/-) model. RHBDL4 deficiency in APPtg mice led to increased total cerebral APP and amyloidogenic processing when compared to APPtg controls. Contrary to expectations, as assessed by cognitive tests, RHBDL4 absence rescued cognition in 5-month-old female APPtg mice. Informed by unbiased RNAseq data, we demonstrated in vitro and in vivo that RHBDL4 absence leads to greater levels of active {beta}-catenin due to decreased proteasomal clearance. Decreased {beta}-catenin activity is known to underlie cognitive defects in APPtg mice and AD. Our work suggests that RHBDL4s increased expression in AD, in addition to regulating APP levels, leads to aberrant degradation of {beta}-catenin, contributing to cognitive impairment.

animal behavior and cognition↗

bioRxiv2023

Eta-secretase-like processing of the amyloid precursor protein (APP) by RHBDL4

The amyloid precursor protein (APP) has been extensively studied with regards to its contribution to the pathology of Alzheimers disease. APP is an ubiquitously expressed type I transmembrane protein synthesized in the endoplasmic reticulum (ER) and translocated to the plasma membrane where it undergoes proteolytic cleavages by several identified proteases. Conversely to other known proteases, we previously elucidated human rhomboid protease RHBDL4 as a novel APP processing enzyme where several cleavages likely occur already in the ER. Interestingly, the pattern of RHBDL4-derived large APP C-terminal fragments resemble those generated by the {eta}-secretase or MT5-MMP, which was described to generate so called A{eta} fragments. The similarity in large APP C-terminal fragments between both proteases raised the question whether RHBDL4 may contribute to {eta}-secretase activity and A{eta}-like fragments. Here, we identified two cleavage sites of RHBDL4 in APP by mass spectrometry, which, intriguingly, lie in close proximity to the cleavage sites of MT5-MMP. Indeed, we observed that RHBDL4 generates A{eta}-like fragments in vitro without contributions of -, {beta}-, or {gamma}-secretases. Such A{eta}-like fragments are likely generated in the ER since RHBDL4-derived APP-C-terminal fragments do not reach the cell surface. Inherited, familial APP mutations appear to not affect this processing pathway. In RHBDL4 knockout mice, we observed increased cerebral full length APP levels in comparison to WT brains in support of RHBDL4 being a physiologically relevant protease for APP. Furthermore, we found secreted A{eta} fragments in dissociated mixed cortical cultures from wild type mice, however significantly less A{eta} fragments in cultures from RHBDL4 knockout mice. Our data underscores that RHBDL4 contributes to {eta}-secretease-like processing of APP and that RHBDL4 is a physiologically relevant protease for APP.

biochemistry↗

bioRxiv2023

CETP inhibitor evacetrapib enters mouse brain tissue

High levels of plasma cholesterol, especially high levels of low-density lipoprotein-cholesterol (LDL-C), have been associated with an increased risk of Alzheimers disease. The cholesteryl ester transfer protein (CETP) in plasma distributes cholesteryl esters between lipoproteins and increases LDL-C in plasma. Epidemiologically, decreased CETP activity has been associated with sustained cognitive performance during aging, longevity, and a lower risk of Alzheimers disease. Thus, pharmacological CETP inhibitors could potentially be repurposed for the treatment of Alzheimers disease as they are safe and effective at lowering CETP activity and LDL-C. While CETP is mostly expressed by the liver and secreted into the bloodstream, CETP is also expressed by astrocytes in the brain. It is therefore important to determine if CETP inhibitors can enter the brain. Here, we describe pharmacokinetic parameters of the CETP inhibitor evacetrapib in plasma, liver, and brain tissues in CETP transgenic mice. We show that evacetrapib crosses the blood-brain barrier and is detectable in brain tissue 0.5 h after a 40 mg/kg i.v. injection in a nonlinear function. We conclude that evacetrapib may prove to be a good candidate to treat CETP-mediated cholesterol dysregulation in Alzheimers disease.

pharmacology and toxicology↗

bioRxiv2020

The Cholesteryl Ester Transfer Protein (CETP) raises Cholesterol Levels in the Brain and affects Presenilin-mediated Gene Regulation.

The cholesteryl ester transfer protein (CETP) is a lipid transfer protein responsible for the exchange of cholesteryl esters and triglycerides between lipoproteins. Decreased CETP activity is associated with longevity, cardiovascular health, and maintenance of good cognitive performance. Interestingly, mice lack the CETP-encoding gene and have very low levels of low-density lipoprotein (LDL) particles compared to humans. To understand how CETP activity affects the brain, we utilised CETP transgenic (CETPtg) mice showing elevated LDL levels on a high cholesterol diet inducing CETP expression. We found that CETPtg mice had up to 25% higher cholesterol levels in the brain. Using a microarray on astrocyte-derived mRNA, we found that this cholesterol increase is likely not due to astrocytic-dependent de novo synthesis of cholesterol. Rather, several genes linked to Alzheimers disease were altered in CETPtg mice. Most interestingly, we found activation of the G-protein coupled receptor EP4 and {gamma}-secretase as upstream regulators of these transcriptional changes. Further in vitro studies showed that CETP expression was sufficient to activate {gamma}-secretase activity. The data suggest that CETP activity affects brains health through modulating cholesterol levels and Alzheimers-related pathways. Therefore, CETPtg mice constitute a valuable research tool to investigate the impact of the cholesterol metabolism on brain functions.

cell biology↗