Newbern, J. M. | Search bioRxiv

bioRxiv2020

TRANSITION OF PODOSOMES INTO ZIPPER-LIKE STRUCTURES INMACROPHAGE-DERIVED MULTINUCLEATED GIANT CELLS

Macrophage fusion resulting in the formation of multinucleated giant cells (MGCs) is a multistage process that requires many adhesion-dependent steps and involves the rearrangement of the actin cytoskeleton. The diversity of actin-based structures and their role in macrophage fusion is poorly understood. In this study, we revealed hitherto unrecognized actin-based zipper-like structures (ZLSs) that arise between MGCs formed on the surface of implanted biomaterials. We established an in vitro model for the induction of these structures in mouse macrophages undergoing IL-4- mediated fusion. Using this model, we show that over time MGCs develop cell-cell contacts containing ZLSs. Live-cell imaging using macrophages isolated from mRFP- or GFP-Lifeact mice demonstrated that ZLSs are dynamic formations undergoing continuous assembly and disassembly and that podosomes are precursors of these structures. Immunostaining experiments showed that vinculin, talin, integrin M{beta}2, and other components of podosomes are present in ZLSs. Macrophages deficient in WASp or Cdc42, two key molecules involved in actin core organization in podosomes, as well as cells treated with the inhibitors of the Arp2/3 complex failed to form ZLSs. Furthermore, E-cadherin and nectin-2 were found between adjoining membranes, suggesting that the transition of podosomes into ZLSs is induced by bridging plasma membranes by junctional proteins.

cell biology↗

bioRxiv2019

Hyperactive MEK1 signaling in cortical GABAergic interneurons causes embryonic parvalbumin-neuron death and deficits in behavioral inhibition

Abnormal ERK/MAPK pathway activity is an important contributor to the neuropathogenesis of many disorders including Fragile X, Rett, 16p11.2 Syndromes, and the RASopathies. Individuals with these syndromes often present with intellectual disability, ADHD, autism, and epilepsy. However, the pathological mechanisms that underly these deficits are not fully understood. Here, we examined whether hyperactivation of MEK1 signaling modifies the development of GABAergic cortical interneurons (CINs), a heterogeneous population of inhibitory neurons necessary for cortical function. We show that GABAergic-neuron specific MEK1 hyperactivation in vivo leads to increased cleaved caspase-3 labeling in a subpopulation of immature neurons in the embryonic subpallium. Adult mutants displayed a significant loss of mature parvalbumin-expressing (PV) CINs, but not somatostatin-expressing CINs, during postnatal development and a modest reduction in perisomatic inhibitory synapse formation on excitatory neurons. Surviving mutant PV-CINs maintained a typical fast-spiking phenotype and minor differences in intrinsic electrophysiological properties. These changes coincided with an increased risk of seizure-like phenotypes. In contrast to other mouse models of PV-CIN loss, we discovered a robust increase in the accumulation of perineuronal nets, an extracellular structure thought to restrict plasticity in the developing brain. Indeed, we found that mutants exhibit a significant impairment in the acquisition of a behavioral test that relies on behavioral response inhibition, a process linked to ADHD-like phenotypes. Overall, our data suggests PV-CIN development is particularly sensitive to hyperactive MEK1 signaling which may underlie neurological deficits frequently observed in ERK/MAPK-linked syndromes.\n\nSignificance StatementThe RASopathies are a family of neurodevelopmental syndromes caused by mutations that lead to increased RAS/RAF/MEK/ERK signaling and are associated with intellectual disability, epilepsy, and ADHD. We do not fully understand how distinct neuronal subtypes are affected in these syndromes. Here, we show that increased MEK signaling in developing mice promotes the embryonic death of a specific subset of cortical inhibitory neurons that express parvalbumin. Surviving mutant parvalbumin neurons also show significant changes in crucial maturation processes, which coincide with increased seizure susceptibility and profound deficits in behavioral inhibition. These data suggest that deficits in inhibitory circuit development contribute to RASopathy neuropathogenesis and indicate that therapeutic strategies targeting inhibitory interneuron dysfunction may be beneficial for these individuals.

neuroscience↗