Biology subjects

Meenderink, L. M.

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

7 recordsLinked to original sources

bioRxiv2025

Brush border intermicrovillar adhesion limits bacterial attachment to the small intestine brush border

Enterocytes present a continuous array of uniform, tightly packed, apical microvilli known as the "brush border". Adjacent microvilli tips are linked by an intermicrovillar adhesion complex (IMAC) composed of cadherins that are required for microvillar packing, length uniformity, and junctional integrity, with disruption linked to intestinal autoimmune disease and infections. We found that IMAC-deficient mice have dysbiosis with increased adherent (actin-dependent) and mucosal (actin-independent) bacteria in the terminal ileum. The bacteria are primarily commensals without differences in diversity between groups. Primary segments of Segmented filamentous bacteria (SFB) recruit the microvilli-associated proteins EPS8 and IRTKS, as well as the Arp2/3 complex, to remodel actin. SFB not only anchor adjacent to epithelial cell junctions but also incorporate ZO-1 into their attachment structures. Together, these data reveal maturation of the SFB-host interface that mirrors the complex SFB lifecycle. Our work indicates a previously unrecognized role for the brush border as a key component of host defense against luminal microbes.

cell biology↗

bioRxiv2024

Apical clathrin-coated endocytic pits control the growth and size of epithelial microvilli

Epithelial cells from diverse contexts assemble apical specializations to serve tissue-specific functions. In virtually all cases, these features consist of arrays of microvilli: micron-scale, actin bundle-supported protrusions that mediate biochemical and physical interactions with the external environment. Despite their importance for epithelial physiology, how microvilli grow during cellular differentiation remains poorly understood. Using genetic and small molecule perturbations, we found that an epithelial cells potential for growing microvilli of normal size is limited by an adjacent actin-dependent process: apical clathrin-mediated endocytosis. Unexpectedly, timelapse imaging of individual microvillar growth events revealed tight spatial and temporal coupling to sites of clathrin-mediated endocytosis. Ultrastructural characterization of undifferentiated epithelial monolayers also showed that most nascent microvilli are in contact with an apical endocytic pit. Finally, inhibition of the Arp2/3 branched nucleation complex, which drives actin polymerization on coated pits, significantly reduced the accumulation of new microvilli on the surface of differentiating epithelial cells. Based on these discoveries, we conclude that clathrin-mediated endocytosis and its associated Arp2/3-based actin nucleation activity control the timing and location of microvillar growth, as well as the dimensions of the resulting protrusions.

cell biology↗

bioRxiv2023

Distinct blood CD3+ CD14+ T Cell-Monocyte complexes harbor HIV and are dynamic, glucose-dependent, and increased in individuals with glucose intolerance

An increased risk of cardiometabolic disease accompanies persistent systemic inflammation. Yet, the innate and adaptive immune system features in persons who develop these conditions remain poorly defined. Doublets, or cell-cell complexes, are routinely eliminated from flow cytometric and other immune phenotyping analyses, which limits our understanding of their relationship to disease states. Using well-characterized clinical cohorts, including participants with controlled HIV as a model for chronic inflammation and increased immune cell interactions, we show that circulating CD14+ monocytes complexed to CD3+ T cells are dynamic, biologically relevant, and increased in individuals with diabetes after adjusting for confounding factors. The complexes form functional immune synapses with increased expression of proinflammatory cytokines and greater glucose utilization. Furthermore, in persons with HIV, the CD3+T-cell: CD14+monocyte complexes had more HIV copies compared to matched CD14+ monocytes or CD4+ T cells alone. Our results demonstrate that circulating CD3+T-cell:CD14+monocyte pairs represent dynamic cellular interactions that may contribute to inflammation and cardiometabolic disease pathogenesis and may originate or be maintained, in part, by chronic viral infections. These findings provide a foundation for future studies investigating mechanisms linking T cell-monocyte cell-cell complexes to developing immune-mediated diseases, including HIV and diabetes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/538020v2_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@fdc324org.highwire.dtl.DTLVardef@168fc4org.highwire.dtl.DTLVardef@138a9a0org.highwire.dtl.DTLVardef@1087108_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LICirculating CD3+ CD14+ T cell-monocyte complexes are higher in individuals with diabetes. C_LIO_LICD3+ CD14+ T cell-monocytes complexes comprise a heterogenous group of functional and dynamic cell-cell interactions. C_LIO_LIThe proportion of CD3+ CD14+ T cell-monocyte complexes is positively associated with fasting blood glucose and negatively with plasma IL-10 levels and CD4+ T regulatory cells. C_LIO_LICD3+ CD14+ T cell-monocyte complexes are metabolically flexible and can utilize both glycolysis and oxidative phosphorylation for their energy requirements. C_LIO_LIIn persons with treated HIV, CD3+ CD14+ T cell-monocytes have more detectable HIV DNA than circulating CD4+ T cells alone. C_LI

immunology↗

bioRxiv2020

Direct visualization of epithelial microvilli biogenesis

Microvilli are actin bundle supported surface protrusions that play essential roles in diverse epithelial cell functions. To develop our understanding of microvilli biogenesis, we used live imaging to directly visualize protrusion growth at early stages of epithelial differentiation. Time-lapse data revealed that an "initiation complex" enriched in EPS8 and IRTKS appears at future sites of microvillus growth minutes before core actin bundle assembly. Elongation of a new core bundle occurs in parallel with the arrival of EZRIN and plasma membrane encapsulation. In addition to de novo growth, we also observed that new microvilli emerge from pre-existing protrusions. Additionally, we found that new microvilli can also collapse, characterized first by loss of membrane wrapping and Ezrin enrichment, followed by a sharp decrease in distal tip EPS8 and IRTKS. These studies are the first to offer a temporally resolved microvillus growth mechanism and highlight critical factors that drive this process.

cell biology↗

bioRxiv2020

Non-muscle myosin-2 contractility-dependent actin turnover limits the length of epithelial microvilli

Epithelial brush borders are large arrays of microvilli that enable efficient solute uptake from luminal spaces. In the context of the intestinal tract, brush border microvilli drive functions that are critical for physiological homeostasis, including nutrient uptake and host defense. However, cytoskeletal mechanisms that regulate the assembly and morphology of these protrusions are poorly understood. The parallel actin bundles that support microvilli have their pointed-end rootlets anchored in a highly crosslinked filamentous meshwork referred to as the "terminal web". Although classic EM studies revealed complex ultrastructure, the composition, organization, and function of the terminal web remains unclear. Here, we identify non-muscle myosin-2C (NM2C) as a major component of the brush border terminal web. NM2C is found in a dense, isotropic layer of puncta across the sub-apical domain, which transects the rootlets of microvillar actin bundles. Puncta in this network are separated by [~]210 nm, dimensions that are comparable to the expected size of filaments formed by NM2C. In primary intestinal organoid cultures, the terminal web NM2C network is highly dynamic and exhibits continuous remodeling. Using pharmacological and genetic perturbations to disrupt NM2C activity in cultured intestinal epithelial cells, we found that this motor controls the length of growing microvilli by regulating actin turnover in a manner that requires a fully active motor domain. Our findings answer a decades old question on the function of terminal web myosin and hold broad implications for understanding apical morphogenesis in diverse epithelial systems.

cell biology↗

bioRxiv2019

PACSIN2-dependent apical endocytosis regulates the morphology of epithelial microvilli

Apical microvilli are critical for the homeostasis of transporting epithelia, yet mechanisms that control the assembly and morphology of these protrusions remain poorly understood. Previous studies in intestinal epithelial cell lines suggested a role for F-BAR domain protein PACSIN2 in normal microvillar assembly. Here we report the phenotype of PACSIN2 KO mice and provide evidence that through its role in promoting apical endocytosis, this molecule functions in controlling microvillar morphology. PACSIN2 KO enterocytes exhibit reduced numbers of microvilli and defects in microvillar ultrastructure, with membranes lifting away from rootlets of core bundles. Dynamin2, a PACSIN2 binding partner, and other endocytic factors were also lost from their normal localization near microvillar rootlets. To determine if loss of endocytic machinery could explain defects in microvillar morphology, we examined the impact of PACSIN2 KD and endocytosis inhibition on live intestinal epithelial cells. These assays revealed that when endocytic vesicle scission fails, tubules are pulled into the cytoplasm and this, in turn, leads to a membrane lifting phenomenon reminiscent of that observed in PACSIN2 KO brush borders. These findings lead to a new model where inward forces generated by endocytic machinery on the plasma membrane control the membrane wrapping of cell surface protrusions.\n\nHighlight for TOCApical microvilli increase the functional surface area of transporting epithelia. Here we report that the F-BAR domain-containing protein PACSIN2, through its ability to promote apical endocytosis, plays a critical role in controlling the morphology of intestinal brush border microvilli.

cell biology↗

bioRxiv2018

Actin dynamics drive microvillar motility and clustering during brush border assembly

During differentiation, transporting epithelial cells generate large arrays of microvilli known as a brush borders to enhance functional capacity. To develop our understanding of brush border formation, we used live cell imaging to visualize apical surface remodeling during early stages of this process. Strikingly, we found that individual microvilli exhibit persistent active motility, translocating across the cell surface at ~0.2 m/min. Perturbation studies with inhibitors and photokinetic experiments revealed that microvillar motility is driven by actin assembly at the barbed-ends of core bundles, which in turn is linked to robust treadmilling of these structures. Because the apical surface of differentiating epithelial cells is crowded with nascent microvilli, persistent motility promotes collisions between protrusions and ultimately leads to their clustering and consolidation into higher order arrays. Thus, microvillar motility represents a previously unrecognized driving force for apical surface remodeling and maturation during epithelial differentiation.

cell biology↗