Biology subjects

Kremneva, E.

Publications and source records attributed to Kremneva, E..

6 recordsLinked to original sources

bioRxiv2025

Disrupted emotional resilience and neurovisceral integration in early small vessel disease

BackgroundCerebral small vessel disease (cSVD) is a prevalent age-related microangiopathy leading to cognitive decline. Beyond established mechanisms and risk factors, disturbances in neurovisceral integration--the brain-body coordination of emotional and cardiovascular responses--may represent a systems-level pathway relevant to cSVD pathogenesis. We therefore investigated whether early cSVD is characterised by altered neurovisceral integration and emotional processing. MethodsEighty-two adults were studied: middle-aged adults with early cSVD (n=37), age-matched adults without brain abnormalities (n=23), and young healthy adults (n=22). Participants completed an ecologically grounded social emotion fMRI paradigm alongside self-report measures of interoception and emotional processing. Neurovisceral integration was operationalised as arousal-related modulation of right anterior insula activity and concurrent heart rate dynamics during the task. ResultsEarly cSVD, but not healthy ageing, was associated with diminished insular encoding of arousal, altered heart-rate dynamics, reduced emotional differentiation, and loss of the age-related positivity effect. Self-report questionnaires showed parallel alterations in everyday functioning. Effects remained significant after adjustment for cardiovascular risk factors and cognitive performance. ConclusionStudy findings indicate disruptions in neurovisceral integration and emotional processing across neural, physiological, and behavioural levels, identifying them as candidate biomarkers of early cSVD and potential targets for preventive interventions.

neuroscience↗

bioRxiv2023

Specialized actin nanoscale layers control focal adhesion turnover

Focal adhesions (FAs) connect inner workings of the cell to the extracellular matrix to control cell adhesion, migration, and mechanosensing1,2. Previous studies demonstrated that FAs contain three vertical layers, which connect extracellular matrix to the cytoskeleton3,4,5. However, cellular processes rely on precisely-regulated FA turnover, but the molecular machineries that control FA assembly and disassembly have remained elusive. By using super-resolution iPALM microscopy, we identified two unprecedented nanoscale layers within FAs, specified by actin filaments bound to tropomyosin isoforms Tpm1.6 and Tpm3.2. The Tpm1.6-actin filaments beneath the previously identified actin-regulatory layer are critical for adhesion maturation and controlled cell motility, whereas the Tpm3.2-actin filament layer towards the bottom of FA facilitates adhesion disassembly. Mechanistically, Tpm3.2 stabilizes KANK-family proteins at adhesions, and hence targets microtubule plus-ends to FAs to catalyse their disassembly. Loss of Tpm3.2 leads to disorganized microtubule network, abnormally stable FAs, and defects in tail retraction during cell migration. Thus, FAs are composed of at least three distinct actin filament layers, each having specific roles in coupling of adhesion to the cytoskeleton, or in controlling adhesion dynamics. In a broader context, these findings demonstrate how distinct actin filament populations can co-exist and perform specific functions within a defined cellular compartment.

cell biology↗

bioRxiv2022

Structural basis underlying specific biochemical activities of non-muscle tropomyosin isoforms

The actin cytoskeleton is critical for cell migration, morphogenesis, endocytosis, organelle dynamics, and cytokinesis. To support diverse cellular processes, actin filaments form a variety of structures with specific architectures and dynamic properties. Key proteins specifying actin filaments are tropomyosins. Non-muscle cells express several functionally non-redundant tropomyosin isoforms, which differentially control the interactions of other proteins, including myosins and ADF/cofilin, with actin filaments. However, the underlying molecular mechanisms have remained elusive. By determining the cryogenic electron microscopy structures of actin filaments decorated by two functionally distinct non-muscle tropomyosin isoforms, Tpm1.6 and Tpm3.2, we reveal that actin filament conformation remains unaffected upon binding. However, Tpm1.6 and Tpm3.2 follow different paths along the major groove of the actin filament, providing an explanation for their incapability to co-polymerize on actin filaments. The structures and biochemical work also elucidate the molecular basis underlying specific roles of Tpm1.6 and Tpm3.2 in myosin II activation and protecting actin filaments from ADF/cofilin-catalysed severing.

biochemistry↗

bioRxiv2022

Activated I-BAR IRSp53 clustering controls the formation of VASP-actin-based membrane protrusions

Filopodia are actin-rich membrane protrusions essential for cell morphogenesis, motility, and cancer invasion. How cells control filopodia initiation on the plasma membrane remains elusive. We performed experiments in cellulo, in vitro and in silico to unravel the mechanism of filopodia initiation driven by the membrane curvature sensor IRSp53. We showed that full-length IRSp53 self-assembles into clusters on membranes depending on PIP2. Using well-controlled in vitro reconstitution systems, we demonstrated that IRSp53 clusters recruit the actin polymerase VASP to assemble actin filaments locally on membranes, leading to the generation of actin-filled membrane protrusions reminiscent of filopodia. By pulling membrane nanotubes from live cells, we observed that IRSp53 can only be enriched and trigger actin assembly in nanotubes at highly dynamic membrane regions. Our work supports a regulation mechanism of IRSp53 in its attributes of curvature sensation and partner recruitment to ensure a precise spatial-temporal control of filopodia initiation.

biophysics↗

bioRxiv2020

Conformational dynamics regulate SHANK3 actin and Rap1 binding

Actin-rich cellular protrusions direct versatile biological processes from cancer cell invasion to dendritic spine development. The stability, morphology and specific biological function of these protrusions are regulated by crosstalk between three main signaling axes: integrins, actin regulators and small GTPases. SHANK3 is a multifunctional scaffold protein, interacting with several actin-binding proteins, and a well-established autism risk gene. Recently, SHANK3 was demonstrated to sequester integrin-activating small GTPases Rap1 and R-Ras to inhibit integrin activity via its N-terminal SPN domain. Here, we demonstrate that SHANK3 interacts directly with actin using its SPN domain. Actin binding can be inhibited by an intramolecular closed conformation of SHANK3, where the adjacent ARR domain covers the actin-binding interface of the SPN domain. Actin and Rap1 compete with each other for binding to SHANK3 and loss of SHANK3-actin binding augments inhibition of Rap1-mediated integrin activity. This dynamic crosstalk has functional implications for filopodia formation in cancer cells, dendritic spine morphology in neurons and autism-linked phenotypes in vivo.

cell biology↗

bioRxiv2019

Carbonic anhydrase VII regulates dendritic spine morphology and density via actin filament bundling

Intracellular pH is a potent modulator of neuronal functions. By catalyzing (de)hydration of CO2, intracellular carbonic anhydrase (CAi) isoforms CAII and CAVII contribute to neuronal pH buffering and dynamics. The presence of two highly active isoforms suggests that they form spatially distinct CAi pools enabling subcellular modulation of pH. Here we show that CAVII, unlike CAII, is localized to the filamentous actin network, and its overexpression induces formation of thick actin bundles and membrane protrusions in fibroblasts. In neurons, CAVII is enriched in dendritic spines, and its over-expression causes aberrant spine morphology. We identified amino acids unique to CAVII that are required for direct actin interactions, promoting actin filament bundling and spine targeting. Lack of CAVII in neocortical neurons leads to reduced spine density and increased proportion of small spines. Thus, our work demonstrates highly distinct subcellular expression patterns of CAII and CAVII, and a novel, structural role of CAVII.

cell biology↗