Distinct niches within the extracellular matrix dictate fibroblast function in (cell free) 3D lung tissue cultures

Cues from the extracellular matrix (ECM) and their functional interplay with cells play pivotal roles for development, tissue repair, and disease. However, the precise nature of this interplay remains elusive. We used an innovative 3D cell culture ECM model by decellularizing 300-µm-thick ex vivo lung tissue scaffolds (d3D-LTCs) derived from diseased and healthy mouse lungs, which widely mimics the native (patho)physiological in vivo ECM microenvironment. We successfully repopulated all d3D-LTCs with primary human and murine fibroblasts, and moreover, we demonstrated that the cells also populated the innermost core regions of the d3D-LTCs in a real 3D fashion. The engrafted fibroblasts revealed a striking functional plasticity, depending on their localization in distinct ECM niches of the d3D-LTCs, affecting the cells' tissue engraftment, cellular migration rates, cell morphologies, and protein expression and phosphorylation levels. Surprisingly, we also observed fibroblasts that were homing to the lung scaffold's interstitium as well as fibroblasts that were invading fibrotic areas. To date, the functional nature and even the existence of 3D cell matrix adhesions in vivo as well as in 3D culture models is still unclear and controversial. Here, we show that attachment of fibroblasts to the d3D-LTCs evidently occurred via focal adhesions, thus advocating for a relevant functional role in vivo. Furthermore, we found that protein levels of talin, paxillin, and zyxin and phosphorylation levels of paxillin Y118, as well as the migration-relevant small GTPases RhoA, Rac, and CDC42, were significantly reduced compared with their attachment to 2D plastic dishes. In summary, our results strikingly indicate that inherent physical or compositional characteristics of the ECM act as instructive cues altering the functional behavior of engrafted cells. Thus, d3D-LTCs might aid to obtain more realistic data in vitro, with a high relevance for drug discovery and mechanistic studies alike.