Biology subjects

Millan, J.

Publications and source records attributed to Millan, J..

6 recordsLinked to original sources

bioRxiv2026

Podoplanin shapes epidermal morphogenesis and coordinates stem cell and epidermal-dermal responses during inflammatory remodelling

Skin development and adaptation to inflammatory stress require keratinocytes to coordinate changes in cell behaviour with tissue organisation. Cell adhesion and the cortical cytoskeleton support the structural plasticity underlying these responses. Here, using complementary mouse models of global podoplanin deletion and conditional deletion in basal keratinocytes driven by keratin 5-Cre (K5Cre), we identify a role for the small transmembrane glycoprotein podoplanin in maintaining basal layer organisation and coordinating differentiation with barrier acquisition during development, as well as in inflammatory skin remodelling. Podoplanin expression was dynamically regulated during epidermal morphogenesis, becoming enriched in basal epithelial compartments before declining postnatally in the interfollicular epidermis. Both deletion models exhibited basal layer disorganisation, altered division orientation and increased epidermal thickness. Premature or expanded expression of differentiation markers was accompanied by delayed barrier acquisition, indicating that podoplanin loss uncouples differentiation marker expression from functional maturation. Barrier function subsequently recovered despite persistent histological abnormalities. In primary keratinocytes, podoplanin deficiency disrupted junctional actin organisation, reduced ERM phosphorylation and impaired junctional enrichment of pERM and doubly phosphorylated myosin light chain 2 (ppMLC2), despite largely preserved recruitment of adhesion proteins. In adult skin, K5Cre-mediated deletion altered differentiation marker dynamics following topical application of the proinflammatory agent 12-O-tetradecanoylphorbol-13-acetate (TPA), while the epidermal thickening response remained largely comparable to controls. These epidermal changes were accompanied by altered dermal thickness dynamics and an absence of TPA-induced podoplanin expression in dermal fibroblasts. Furthermore, TPA reduced the number of BrdU-retaining cells in the interfollicular epidermis of controls but not K5Cre-mediated conditional podoplanin knockout mice. This difference is consistent with impaired activation or mobilisation of slow-cycling cells, suggesting altered responsiveness within the epidermal stem and progenitor compartment. Together, these findings establish keratinocyte-expressed podoplanin as a regulator of epidermal organisation and functional maturation, with effects extending beyond the epithelium to shape the dermal response to inflammatory challenge.

cell biology↗

bioRxiv2024

Role of ERK2 dimerization in synaptic plasticity and memory

Extensive research has focused on extracellular-signal regulated kinase (ERK) 1/2 phosphorylation across various memory and plasticity models. However, the precise mechanisms linking ERK activity to memory stabilization and restabilization are still poorly understood, and the role of ERK1/2 dimerization remains unexplored. ERK dimerization is essential for the binding and activation of cytoplasmic targets, many of which are involved in memory and plasticity. In this study, we investigated the role of ERK2 dimerization in long-term memory and synaptic plasticity. We found that reactivation of a weak inhibitory avoidance (wIA) memory led to a significant reduction in hippocampal ERK2 dimerization. Furthermore, intrahippocampal infusion of DEL-22379 (DEL), an ERK dimerization inhibitor, following memory reactivation had a bidirectional effect: it blocked the reconsolidation of a strong inhibitory avoidance (sIA) memory but enhanced the reconsolidation of a wIA memory. Moreover, DEL administration blocked hippocampal ERK2 dimerization in vivo and impaired high-frequency stimulation-induced long-term potentiation (LTP) in hippocampal slices. These findings demonstrate that ERK2 dimerization occurs in the intact mouse nervous system and plays a pivotal role in plasticity and memory. While further research is needed, this study highlights the relevance of ERK dimerization in these processes.

neuroscience↗

bioRxiv2024

Harnessing homeostatically active RhoC at cell junctions preserves human endothelial barrier function during inflammation

Rho GTPases are molecular targets of bacterial toxins that modulate their enzymatic activity. RhoA, RhoB and RhoC are almost identical and play critical roles in generating actomyosin-mediated contractile forces that cause endothelial hyperpermeability during inflammation. Searching for new treatments to modulate endothelial integrity, we demonstrate that the specific and simultaneous activation of these three Rho GTPases with a chimeric recombinant toxin does not induce cell contraction but enhances homeostatic endothelial barrier function, increases reticular adherens junctions and preserves the microvascular endothelium in response to pathological inflammatory challenges in vitro and in vivo. This pro-barrier effect is specifically mediated by RhoC, whose activity is increased by cell confluence. The uniqueness of RhoC relies on an arginine 188 within its hypervariable region that determines its junctional localization, high homeostatic activity, and barrier-protective function. Quantitative proteomics revealed that RhoC regulates the expression of myosin light chain proteins and junction-stabilizing actomyosin. Thus, harnessing the activity of RhoC represents a potential therapy for strengthening endothelial barriers during pathological inflammation.

cell biology↗

bioRxiv2023

ICAM-1 nanoclusters regulate hepatic epithelial cell polarity by leukocyte adhesion-independent control of apical actomyosin

Epithelial Intercellular Adhesion Molecule (ICAM)-1 is apically polarized, interacts with and guides leukocytes across epithelial barriers. Polarized hepatic epithelia organize their apical membrane domain into bile canaliculi and ducts, which are not accessible to circulating immune cells but that nevertheless confine most of ICAM-1. Here, by analyzing ICAM-1_KO human hepatic cells, liver organoids from ICAM-1_KO mice and rescue-of-function experiments, we show that ICAM-1 regulates epithelial apicobasal polarity in a leukocyte adhesion-independent manner. ICAM-1 signals to an actomyosin network at the base of canalicular microvilli, thereby controlling the dynamics and size of bile canalicular-like structures (BCs). We identified the scaffolding protein EBP50/NHERF1/SLC9A3R1, which connects membrane proteins with the underlying actin cytoskeleton, in the proximity interactome of ICAM-1. EBP50 and ICAM-1 form nano-scale domains that overlap in microvilli, from which ICAM-1 regulates EBP50 nano-organization. Indeed, EBP50 expression is required for ICAM-1-mediated control of BC morphogenesis and actomyosin. Our findings indicate that ICAM-1 regulates the dynamics of epithelial apical membrane domains beyond its role as a heterotypic cell-cell adhesion molecule and reveal potential therapeutic strategies for preserving epithelial architecture during inflammatory stress.

cell biology↗

bioRxiv2022

p73 controls cell junction dynamics during sprouting angiogenesis and acts via Angiomotin

Preservation of blood vessels integrity, which is critical for normal physiology and organ function, is controlled at multiple levels, including endothelial junctions. However, the mechanism that controls the adequate assembly of endothelial cell junctions is not fully defined. Here we uncover TAp73 transcription factor as a vascular architect that orchestrates transcriptional programs involved in cell junction establishment and developmental blood vessel morphogenesis and identify Angiomotin (AMOT) as a TAp73 direct transcriptional target. Knockdown of p73 in endothelial cells not only results in decreased Angiomotin expression and localization at intercellular junctions, but also affects its downstream function regarding Yes-Associated Protein (YAP) cytoplasmic sequestration upon cell-cell contact. Analysis of adherens junctional morphology after p73-knockdown in human endothelial cells revealed striking alterations, particularly a sharp increase in serrated junctions and actin bundles appearing as stress fibers, both features associated with enhanced barrier permeability. In turn, stabilization of Angiomotin levels rescued those junctional defects, confirming that TAp73 controls endothelial junction dynamics, at least in part, through the regulation of Angiomotin. The observed defects in monolayer integrity were linked to hyperpermeability and reduced transendothelial electric resistance. Moreover, p73-knockout retinas showed a defective sprout morphology coupled to hemorrhages, highlighting the physiological relevance of p73 regulation in the maintenance of vessel integrity in vivo. We propose a new model in which TAp73 acts as a vascular architect integrating transcriptional programs that will impinge with Angiomotin/YAP signaling to maintain junctional dynamics and integrity, whilst balancing endothelial cell rearrangements in angiogenic vessels.

cell biology↗

bioRxiv2020

USH2A is a Meissner corpuscle end-organ protein necessary for vibration sensing in mice and humans

Fingertip mechanoreceptors comprise sensory neuron endings together with specialized skin cells that form the end-organ. Exquisitely sensitive vibration-sensing neurons are associated with Meissners corpuscles and Pacinian corpuscles1. Such end-organ structures have been recognized for more than 160 years, but their exact functions have remained a matter of speculation. Here we examined the role of USH2A in touch sensation in humans and mice. The USH2A gene encodes a transmembrane protein with a very large extracellular domain. Pathogenic USH2A mutations cause Usher syndrome associated with hearing loss and visual impairment2. We show that patients with biallelic pathogenic USH2A mutations also have profound impairments in vibrotactile touch perception. Similarly, mice lacking the USH2A protein showed severe deficits in a forepaw vibrotactile discrimination task. Forepaw rapidly-adapting mechanoreceptors (RAMs) recorded from Ush2a-/- mice innervating Meissners corpuscles showed profound reductions in their vibration sensitivity. However, the USH2A protein was not expressed in sensory neurons, but was found in specialized terminal Schwann cells in Meissners corpuscles. Loss of this large extracellular tether-like protein in corpuscular end-organs innervated by RAMs was sufficient to reduce the vibration sensitivity of mechanoreceptors. Thus, USH2A expressed in corpuscular end-organs associated with vibration sensing is required to properly perceive vibration. We propose that cells within the corpuscle present a tether-like protein that may link to mechanosensitive channels in sensory endings to facilitate small amplitude vibration detection essential for the perception of fine textured surfaces.

neuroscience↗