Biology subjects

Mitchel, J. A.

Publications and source records attributed to Mitchel, J. A..

4 recordsLinked to original sources

bioRxiv2022

In airway epithelium, basal stem cells and their stress fibers remodel during the unjamming transition

Under homeostatic conditions, epithelial cells remain non-migratory. However, during embryonic developmental and pathological processes, they become migratory. The mechanism underlying the transition between non-migratory and migratory epithelial cells is a fundamental question of cellular biology. In well-differentiated primary human bronchial epithelial cell layers, non-migratory epithelial cells become migratory through an unjamming transition (UJT). We have previously identified the hallmarks of UJT: apical cell elongation and collective cellular migration. These indicate that UJT is driven by intercellular force modulation, but the nature of these forces in pseudostratified epithelia is unknown. Here, we identify structural characteristics of basal stem cells that are indicative of force generation. During the UJT, basal stem cells elongate and enlarge, and their stress fibers lengthen and align. These morphological changes in basal stem cells correspond to the previously defined hallmarks of the UJT. Moreover, basal cell elongation and stress fiber lengthening precedes apical cell elongation. Together, these structural changes in basal stem cells suggest that in pseudostratified airway epithelium, basal stem cells may be the origin of the traction forces through stress fiber modeling during the UJT. Summary StatementOur image analysis of pseudostratified airway epithelium reveals basal stem cells as the likely source of traction forces driving collective cellular migration during an unjamming transition.

cell biology↗

bioRxiv2020

Epithelial layer unjamming shifts energy metabolism toward glycolysis

In development of an embryo, healing of a wound, or progression of a carcinoma, a requisite event is collective epithelial cellular migration. For example, cells at the advancing front of a wound edge tend to migrate collectively, elongate substantially, and exert tractions more forcefully compared with cells many ranks behind. With regards to energy metabolism, striking spatial gradients have recently been reported in the wounded epithelium, as well as in the tumor, but within the wounded cell layer little is known about the link between mechanical events and underlying energy metabolism. Using the advancing confluent monolayer of MDCKII cells as a model system, here we report at single cell resolution the evolving spatiotemporal fields of cell migration speeds, cell shapes, and traction forces measured simultaneously with fields of multiple indices of cellular energy metabolism. Compared with the epithelial layer that is unwounded, which is non-migratory, solid-like and jammed, the leading edge of the advancing cell layer is shown to become progressively more migratory, fluid-like, and unjammed. In doing so the cytoplasmic redox ratio becomes progressively smaller, the NADH lifetime becomes progressively shorter, and the mitochondrial membrane potential and glucose uptake become progressively larger. These observations indicate that a metabolic shift toward glycolysis accompanies collective cellular migration but show, further, that this shift occurs throughout the cell layer, even in regions where associated changes in cell shapes, traction forces, and migration velocities have yet to penetrate. In characterizing the wound healing process these morphological, mechanical, and metabolic observations, taken on a cell-by-cell basis, comprise the most comprehensive set of biophysical data yet reported. Together, these data suggest the novel hypothesis that the unjammed phase evolved to accommodate fluid-like migratory dynamics during episodes of tissue wound healing, development, and plasticity, but is more energetically expensive compared with the jammed phase, which evolved to maintain a solid-like non-migratory state that is more energetically economical. Two sentence summaryAt the leading front of an advancing confluent epithelial layer, each cell tends to migrate, elongate, and pull on its substrate far more than do cells many ranks behind, but little is known about underlying metabolic events. Using the advancing monolayer of MDCKII cells as a model of wound healing, here we show at single cell resolution that physical changes associated with epithelial layer unjamming are accompanied by an overall shift toward glycolytic metabolism.

biophysics↗

bioRxiv2019

The unjamming transition is distinct from the epithelial-to-mesenchymal transition.

Every organ surface and body cavity is lined by a confluent collective of epithelial cells. In homeostatic circumstances the epithelial collective remains effectively solid-like and sedentary. But during morphogenesis, remodeling or repair, as well as during malignant invasion or metastasis, the epithelial collective becomes fluid-like and migratory1-4. This conversion from sedentary to migratory behavior has traditionally been understood as a manifestation of the epithelial-to-mesenchymal transition (EMT) or the partial EMT (pEMT)5-8. However, in certain contexts this conversion has been attributed to the recently discovered unjamming transition (UJT), in which epithelial cells move collectively and cooperatively9-11. UJT and pEMT share certain aspects of collective cellular migration, but the extent to which these processes are distinct, overlapping or perhaps even identical has remained undefined. Using the confluent layer of well-differentiated primary human bronchial epithelial (HBE) cells, here we triggered UJT by exposing the sedentary layer to mechanical compression9-12. Cells thereafter migrated cooperatively, aligned into packs locally, and elongated systematically. Nevertheless, cell-cell junctions, apico-basal polarity, and barrier function remained intact in response, and mesenchymal markers remained unapparent. As such, pEMT was not evident. When we triggered pEMT and associated cellular migration by exposing the sedentary layer to TGF-{beta}1, metrics of UJT versus pEMT diverged. To account for these striking physical observations a new mathematical model attributes the effects of pEMT mainly to diminished junctional tension but attributes those of UJT mainly to augmented cellular propulsion. Together, these findings establish that UJT is sufficient to account for vigorous epithelial layer migration even in the absence of pEMT. Distinct gateways to cellular migration therefore become apparent - UJT as it might apply to migration of epithelial sheets, and EMT/pEMT as it might apply to migration of mesenchymal cells on a solitary or collective basis, activated during development, remodeling, repair or tumor invasion. Through the actions of UJT and pEMT working independently, sequentially, or interactively, living tissue is therefore seen to comprise an active engineering material whose modules for plasticity, self-repair and regeneration, are far richer than had been previously appreciated.

biophysics↗

bioRxiv2018

The tumor suppressor p53 promotes carcinoma invasion and collective cellular migration

SummaryLoss of function of the tumor suppressor p53 is generally thought to increase cell motility and invasiveness. Using 2-D confluent and 3-D spheroidal cell motility assays with bladder carcinoma cells and colorectal carcinoma cells, we report, to the contrary, that loss of p53 can decrease cell motility and invasion.\n\nAbstractFor migration of the single cell studied in isolation, loss of function of the tumor suppressor p53 is thought to increase cell motility. Here by contrast we used the 2-D confluent cell layer and the 3-D multicellular spheroid to investigate how p53 impacts dissemination and invasion of cellular collectives. We used two human carcinoma cell lines, the bladder carcinoma EJ and the colorectal carcinoma HCT116. We began by replicating single cell invasion in the traditional Boyden chamber assay, and found that the number of invading cells increased with loss of p53, as expected. In the confluent 2-D cell layer, however, for both EJ and HCT, speeds and effective diffusion coefficients for the p53 null types compared to their p53 expressing counterparts were significantly smaller. Compared to p53 expressers, p53 null cells exhibited more organized cortical actin rings together with reduced front-rear cell polarity. Furthermore, loss of p53 caused cells to exert smaller traction forces upon their substrates, and reduced formation of cryptic lamellipodia. In a 3-D collagen matrix, p53 consistently promoted invasion of the multicellular spheroids into surrounding matrix. Together, these results show that p53 expression in these carcinoma model systems increases collective cellular migration and invasion. As such, these studies point to paradoxical contributions of p53 in single cell versus collective cellular migration.

cancer biology↗