The effect of AKT in extracellular matrix stiffness induced osteogenic differentiation of hBMSCs

The physiological effect of polystyrene nanoplastic particles on fish and human fibroblasts

Numerous studies have identified the detrimental effects for the biosphere of large plastic debris, the effect of microplastics (MPs) and nanoplastics (NPs) is less clear. The skin is the first point of contact with NPs, and skin fibroblasts have a vital role in maintaining skin structure and function. Here, a comparative approach is taken using three fibroblast cell lines from the zebrafish (SJD.1), human male newborn (BJ-5ta) and female adult (HDF/TERT164) and their response to polystyrene NP (PS-NPs) exposure is characterized. Cells were exposed to environmentally relevant PS-NP sizes (50, 500 and 1000 nm) and concentrations (0.001 to 10 μg/ml) and their uptake (1000 nm), and effect on cell viability, proliferation, migration, reactive oxygen species (ROS) production, apoptosis, alkaline phosphatase (ALP) and acid phosphatase (AP) determined. All fibroblasts took up PS-NPs, and a relationship between PS-NP particle size and concentration and the inhibition of proliferation and cell migration was identified. The inhibitory effect of PS-NPs on proliferation was more pronounced for human skin fibroblasts. The presence of PS-NPs negatively affected fibroblast migration in a time-, size- and concentration-dependent manner with larger PS-NPs at higher concentrations causing a more significant inhibition of cell migration, with human fibroblasts being the most affected. No major changes were detected in ROS production or apoptosis in NP challenged fibroblasts. While the ALP activity was increased in all fibroblast cell lines, only fish fibroblasts showed a significant increase in AP activity. The heterogeneous response of fibroblasts induced by PS-NPs was clearly revealed by the segregation of HDF, BJ.5ta and SJD.1 fibroblasts in principal component analysis. Our results demonstrate that PS-NP exposure adversely affected cellular processes in a cell-type and dose-specific manner in distinct fibroblast cell lines, emphasizing the need for further exploration of NP interactions with different cell types to better understand potential implications for human health.

An engineered lamellar bone mimicking full-scale hierarchical architecture for bone regeneration

Lamellar bone, compactly and ingeniously organized in the hierarchical pattern with 6 ordered scales, is the structural motif of mature bone. Each hierarchical scale exerts an essential role in determining physiological behavior and osteogenic bioactivity of bone. Engineering lamellar bone with full-scale hierarchy remains a longstanding challenge. Herein, using bioskiving and mineralization, we attempt to engineer compact constructs resembling full-scale hierarchy of lamellar bone. Through systematically investigating the effect of mineralization on physicochemical properties and bioactivities of multi-sheeted collagen matrix fabricated by bioskiving, the hierarchical mimicry and hierarchy-property relationship are elucidated. With prolongation of mineralization, hierarchical mimicry and osteogenic bioactivity of constructs are performed in a bidirectional manner, i.e. first rising and then descending, which is supposed to be related with transformation of mineralization mechanism from nonclassical to classical crystallization. Construct mineralized 9 days can accurately mimic each hierarchical scale and efficiently promote osteogenesis. Bioinformatic analysis further reveals that this construct potently activates integrin α5-PI3K/AKT signaling pathway through mechanical and biophysical cues, and thereby repairing critical-sized bone defect. The present study provides a bioinspired strategy for completely resembling complex hierarchy of compact mineralized tissue, and offers a critical research model for in-depth studying the structure-function relationship of bone.

Guideline for design of substrate stiffness for mesenchymal stem cell culture based on heterogeneity of YAP and RUNX2 responses

Mesenchymal stem cells (MSCs) have the potential for self-renewal and multipotency to differentiate into various lineages. Thus, they are of great interest in regenerative medicine as a cell source for tissue engineering. Substrate stiffness is one of the most extensively studied exogenous physical factors; however, consistent results have not always been reported for controlling MSCs. Conventionally used stiff culture substrates, such as tissue-culture polystyrene and glass, enhance nuclear localization of a mechanotransducer YAP and a pre-osteogenic transcription factor RUNX2, and bias MSCs towards the osteogenic lineage, even without osteogenic-inducing soluble factors. The mechanosensitive nature and intrinsic heterogeneity present challenges for obtaining reproducible results. This review summarizes the heterogeneity in human MSC response, specifically, nuclear/cytoplasmic localization changes in the mechanotransducer yes-associated protein (YAP) and the osteogenic transcription factor RUNX2, in response to substrate stiffness. In addition, a perspective on the intracellular factors attributed to response heterogeneity is discussed. The optimal range of stiffness parameters, Young's modulus, for MSC expansion culture to suppress osteogenic differentiation bias through the suppression of YAP and RUNX2 nuclear localization, and cell cycle progression is likely to be surprisingly narrow for a cell population from an identical donor and vary among cell populations from different donors. We believe that characterization of the heterogeneity of MSCs and understanding their biological meaning is an exciting research direction to establish guidelines for the design of culture substrates for the sophisticated control of MSC properties.