Biology subjects

Eickholt, B. J.

Publications and source records attributed to Eickholt, B. J..

6 recordsLinked to original sources

bioRxiv2026

Comparative analysis of neuronal proteolytic pathways reveals neuron-specific and sub-compartmental-specific capacities with aging

Proteostasis is essential for maintaining neuronal function, and its dysregulation is a hallmark of aging and neurodegeneration. The ubiquitin-proteasome system (UPS) and macroautophagy are the two major proteolytic pathways responsible for protein degradation. However, their capacity and regulation differ between cell types and across aging. To elucidate the activity of both proteolytic pathways with aging, we performed a comparative analysis of the activity of UPS and macroautophagy in distinct neuronal subcellular compartments, in the cytosol and at synaptic terminals, across aging in neurons of Mus musculus (mouse) and Caenorhabditis elegans (nematode). In mice, our results identified differences between brain areas. While the cortical proteasomal activity declined with aging in both the cytoplasmic as well as synaptic neuronal subcompartments, the cerebellar proteasomal activity decreased only in the cytoplasmic compartment with aging. In C. elegans, we detected a decrease of proteasomal activity in both cytoplasmic and synaptic compartments of neurons. Interestingly, we observed a dysregulation of macroautophagy in both neuronal subcompartments of the cortex and cerebellum in mice as well as in C. elegans neurons with aging. Thus, we uncovered neuron-specific and subcompartmental-specific proteolytic capacities with aging that could manifest in different neuronal vulnerabilities for proteotoxic challenges with aging.

biochemistry↗

bioRxiv2025

Membrane protein condensates polymerize actin and form filopodia

Neuronal morphogenesis is guided by filopodia, dynamically generated plasma membrane protrusions filled with parallel actin filaments. However, how filopodial actin filaments are locally produced, organized, and maintained remains unclear. The transmembrane protein PLPPR3 induces filopodia in neurons and other cells. We find that the intracellular domain (ICD) of PLPPR3 forms liquid condensates, which exhibit strong co-partitioning of actin monomers. These condensates promote actin polymerization within the condensates at the expense of actin monomers in the environment, consistent with thermodynamic coupling of actin partitioning and polymerization, which we recapitulate in a modified polymerization kinetics model. This mechanism requires favorable actin partitioning into the condensate relative to the environment. Using crosslinking mass spectrometry, we identify a WH2-like actin-affinity domain within the PLPPR3 ICD. Deleting this domain lowers actin partitioning in vitro and decreases filopodia formation in vivo. Our findings establish a previously unrecognized mechanism for actin network remodeling, in which condensates act as actin sinks, locally boosting monomer concentrations and facilitating polymerization of actin filaments. One sentence summaryOur study uncovers PLPPR3 condensates to locally enrich actin monomers and promote actin polymerization, driving actin network remodeling and neuronal filopodia formation.

cell biology↗

bioRxiv2021

Input to layer 1 of somatosensory cortex: Local input outweighs long-range and can modulate the activity of layer 1 interneurons

Neocortical Layer (L) 1 has been proposed to be at the center for top-down and bottom-up integration. It is a locus for interactions between long-range inputs, L1 interneurons and apical tuft dendrites of pyramidal neurons. While input to L1 has been studied intensively, the level and effect of input to this layer has still not been completely characterized. Here we examined the input to L1 of mouse somatosensory cortex with retrograde tracing and optogenetics. Our assays reveal that local input to L1 is predominantly from L2/3 and L5 pyramidal neurons and interneurons, and that subtypes of local L5 and L6b neurons project to L1 with different probabilities. Long-range input from sensory-motor cortices to L1 of S1 arose predominantly from L2/3 neurons. Our optogenetic experiments showed that intra-telencephalic L5 pyramidal neurons drive L1 interneurons but have no effect locally on L5 apical tuft dendrites. Dual retrograde tracing revealed that a fraction of local and long-range neurons were both presynaptic to L5 neurons and projected to L1. Our work highlights the prominent role of local inputs to L1 and shows the potential for complex interactions between long-range and local inputs which are both in position to modify the output of somatosensory cortex.

neuroscience↗

bioRxiv2021

Precursor types predict the stability of neuronal branches

Branches are critical for neuron function, generating the morphological complexity required for functional networks. They emerge from different, well-described, cytoskeletal precursor structures that elongate to branches. While branches are thought to be maintained by shared cytoskeletal regulators, our data from mouse hippocampal neurons indicate that the precursor structures trigger alternative branch maintenance mechanisms with differing stabilities. While branches originating from lamellipodia or growth cone splitting events collapse soon after formation, branches emerging from filopodia persist. Furthermore, compared to other developing neurites, axons stabilise all branches and preferentially initiate branches from filopodia. These differences explain the decreased stability of branches we observe in neurons lacking the plasma membrane protein phospholipid phosphatase related protein 3 (PLPPR3/PRG2). Rather than altering branch stability directly, PLPPR3 boosts a filopodia branch program on axons, thereby indirectly initiating more long-lived branches. We propose that studies on branching should distinguish overall stabilising effects from effects on precursor types, ideally using multifactorial statistical models as exemplified in this study.

cell biology↗

bioRxiv2020

Drebrin mediates scar formation and astrocyte reactivity during brain injury by inducing RAB8 tubular endosomes

The brain of mammals lacks a significant ability to regenerate neurons and is thus particularly vulnerable. To protect the brain from injury and disease, damage control by astrocytes through astrogliosis and scar formation is vital. Here, we show that brain injury triggers an ad hoc upregulation of the actin-binding protein Drebrin (DBN) in astrocytes, which is essential for the formation and maintenance of glial scars in vivo. In turn, DBN loss leads to defective glial scar formation and excessive neurodegeneration following mild brain injuries. At the cellular level, DBN switches actin homeostasis from ARP2/3-dependent arrays to microtubule-compatible scaffolds and facilitates the formation of RAB8-positive membrane tubules. This injury-specific RAB8 membrane compartment serves as hub for the trafficking of surface proteins involved in astrogliosis and adhesive responses, such as {beta}1-integrin. Our work identifies DBN as pathology-specific actin regulator, and establishes DBN-dependent membrane trafficking as crucial mechanism in protecting the brain from escalating damage following traumatic injuries.

neuroscience↗

bioRxiv2019

PI 3-kinase delta enhances axonal PIP3 to support axon regeneration in the adult CNS

Peripheral nervous system (PNS) neurons support axon regeneration into adulthood, whereas central nervous system (CNS) neurons lose regenerative ability after development. To better understand this decline whilst aiming to improve regeneration, we focused on phosphoinositide 3-kinase (PI3K) and its product phosphatidylinositol(3,4,5)-trisphosphate (PIP3). We found that neuronal PIP3 decreases with maturity in line with regenerative competence, firstly in the cell body and subsequently in the axon. We show that adult PNS neurons utilise two catalytic subunits of PI3K for efficient regeneration: p110 and p110{delta}. Overexpressing p110 in CNS neurons had no effect, however expression of p110{delta} restored axonal PIP3 and enhanced CNS regeneration in rat and human neurons and in transgenic mice, functioning in the same way as the hyperactivating H1047R mutation of p110. Furthermore, viral delivery of p110{delta} promoted robust regeneration after optic nerve injury. These findings demonstrate a deficit of axonal PIP3 as a reason for intrinsic regeneration failure and show that native p110{delta} facilitates axon regeneration by functioning in a hyperactive fashion.

neuroscience↗