Biology subjects

Berdichevsky, Y.

Publications and source records attributed to Berdichevsky, Y..

3 recordsLinked to original sources

bioRxiv2023

A dynamic balance between neuronal death and clearance after acute brain injury

After acute brain injury, neuronal apoptosis may overwhelm the capacity for microglial phagocytosis, creating a queue of dying neurons awaiting clearance. The size of this queue should be equally sensitive to changes in neuronal death and the rate of phagocytosis. Using rodent organotypic hippocampal slice cultures as a model of acute perinatal brain injury, serial imaging demonstrated that the capacity for microglial phagocytosis of dying neurons was overwhelmed for two weeks. Altering phagocytosis rates, e.g. by changing the number of microglia, dramatically changed the number of visibly dying neurons. Similar effects were generated when the visibility of dying neurons was altered by changing the membrane permeability for vital stains. Canonically neuroprotective interventions such as seizure blockade and neurotoxic maneuvers such as perinatal ethanol exposure were mediated by effects on microglial activity and the membrane permeability of apoptotic neurons, and had either no or opposing effects on healthy surviving neurons. SignificanceAfter acute brain injury, microglial phagocytosis is overwhelmed by the number of dying cells. Under these conditions, the assumptions on which assays for neuroprotective and neurotoxic effects are based are no longer valid. Thus longitudinal assays of healthy cells, such as assessment of the fluorescence emission of transgenically-expressed proteins, provide more accurate estimates of cell death than do single-time-point anatomical or biochemical assays. More accurate estimates of death rates will increase the translatability of preclinical studies of neuroprotection and neurotoxicity.

neuroscience↗

bioRxiv2022

Localized network hyperconnectivity leads to hyperexcitability after injury

Brain injury increases the risk of the development of epilepsy. Axonal sprouting and synaptogenesis are homeostatically mediated responses by neurons to injury-induced de-afferentation and de-efferentation. Rewiring which occurs due to axonal sprouting and synaptogenesis may alter network excitability and lead to epilepsy. Excitatory and inhibitory connectivity are both subject to homeostatic rewiring. Thus, post-sprouting hyperexcitability cannot be simply explained as result of altered inhibitory/excitatory balance. In this work, we show computationally and experimentally that hyperconnected local networks are created by homeostatic rewiring near the injury site. These local networks are characterized by altered system dynamics despite preservation of excitatory/inhibitory balance. Hyperconnected local networks have a lower threshold for burst initiation, and generate spontaneous bursts, which in turn ignite seizure-like activity in the larger network. Our findings demonstrate a novel network mechanism of hyperexcitability and seizure generation due to maladaptive recovery after injury.

neuroscience↗

bioRxiv2022

Polyalanine disease mutations impair UBA6-dependent ubiquitination

Expansion mutations in polyalanine stretches are now associated with a growing number of human diseases with common genotypes and similar phenotypes 1-6. These similarities prompted us to query the normal function of physiological polyalanine stretches, and investigate whether a common molecular mechanism is involved in these diseases. Here, we show that UBA6, an E1 ubiquitin-activating enzyme 7, 8, recognizes a polyalanine stretch within its cognate E2 ubiquitin-conjugating enzyme, USE1. Aberrations in this polyalanine stretch reduced ubiquitin transfer to USE1 and downstream target, the E3 ubiquitin ligase, E6AP. Intriguingly, we identified competition for the UBA6-USE1 interaction by various proteins with polyalanine expansion mutations in the disease state. In mouse primary neurons, the deleterious interactions of expanded polyalanine proteins with UBA6, alter the levels and ubiquitination-dependent degradation of E6AP, which in turn affected the levels of the synaptic protein, Arc. These effects could be observed in induced pluripotent stem cell-derived autonomic neurons from patients with polyalanine expansion mutations. Our results suggest a shared mechanism for such mutations, which may contribute to the congenital malformations seen in polyalanine diseases.

cell biology↗