Non-invasive single-cell biomechanical analysis using live-imaging datasets

May the Force Be with You (Or Not): The Immune System under Microgravity

All terrestrial organisms have evolved and adapted to thrive under Earth's gravitational force. Due to the increase of crewed space flights in recent years, it is vital to understand how the lack of gravitational forces affects organisms. It is known that astronauts who have been exposed to microgravity suffer from an array of pathological conditions including an impaired immune system, which is one of the most negatively affected by microgravity. However, at the cellular level a gap in knowledge exists, limiting our ability to understand immune impairment in space. This review highlights the most significant work done over the past 10 years detailing the effects of microgravity on cellular aspects of the immune system.

Characterization of heterogeneous primary human cartilage-derived cell population using non-invasive live-cell phase-contrast time-lapse imaging

Reliable and reproducible cell therapy strategies to treat osteoarthritis demand an improved characterization of the cell and heterogeneous cell population resident in native cartilage tissue. Using live-cell phase-contrast time-lapse imaging (PC-TLI), this study investigates the morphological attributes and biological performance of the three primary biological objects enzymatically isolated from primary human cartilage: connective tissue progenitors (CTPs), non-progenitors (NPs) and multi-cellular structures (MCSs). The authors' results demonstrated that CTPs were smaller in size in comparison to NPs (P < 0.001). NPs remained part of the adhered cell population throughout the cell culture period. Both NPs and CTP progeny on day 8 increased in size and decreased in circularity in comparison to their counterparts on day 1, although the percent change was considerably less in CTP progeny (P < 0.001). PC-TLI analyses indicated three colony types: single-CTP-derived (29%), multiple-CTP-derived (26%) and MCS-derived (45%), with large heterogeneity with respect to cell morphology, proliferation rate and cell density. On average, clonal (CL) (P = 0.009) and MCS (P = 0.001) colonies exhibited higher cell density (cells per colony area) than multi-clonal (MC) colonies; however, it is interesting to note that the behavior of CL (less cells per colony and less colony area) and MCS (high cells per colony and high colony area) colonies was quite different. Overall effective proliferation rate (EPR) of the CTPs that formed CL colonies was higher than the EPR of CTPs that formed MC colonies (P = 0.02), most likely due to CTPs with varying EPR that formed the MC colonies. Finally, the authors demonstrated that lag time before first cell division of a CTP (early attribute) could potentially help predict its proliferation rate long-term. Quantitative morphological characterization using non-invasive PC-TLI serves as a reliable and reproducible technique to understand cell heterogeneity. Size and circularity parameters can be used to distinguish CTP from NP populations. Morphological cell and colony features can also be used to reliably and reproducibly identify CTP subpopulations with preferred proliferation and differentiation potentials in an effort to improve cell manufacturing and therapeutic outcomes.

Deconstructing Immune Microenvironments of Lymphoid Tissues for Reverse Engineering

The immune microenvironment presents a diverse panel of cues that impacts immune cell migration, organization, differentiation, and the immune response. Uniquely, both the liquid and solid phases of every specific immune niche within the body play an important role in defining cellular functions in immunity at that particular location. The in vivo immune microenvironment consists of biomechanical and biochemical signals including their gradients, surface topography, dimensionality, modes of ligand presentation, and cell-cell interactions, and the ability to recreate these immune biointerfaces in vitro can provide valuable insights into the immune system. This manuscript reviews the critical roles played by different immune cells and surveys the current progress of model systems for reverse engineering of immune microenvironments with a focus on lymphoid tissues.

In Vitro Immune Organs-on-Chip for Drug Development: A Review

The current drug development practice lacks reliable and sensitive techniques to evaluate the immunotoxicity of drug candidates, i.e., their effect on the human immune system. This, in part, has resulted in a high attrition rate for novel drugs candidates. Organ-on-chip devices have emerged as key tools that permit the study of human physiology in controlled in vivo simulating environments. Furthermore, there has been a growing interest in developing the so called "body-on-chip" devices to better predict the systemic effects of drug candidates. This review describes existing biomimetic immune organs-on-chip, highlights their physiological relevance to drug development and discovery and emphasizes the need for developing comprehensive immune system-on-chip models. Such immune models can enhance the performance of novel drug candidates during clinical trials and contribute to reducing the high attrition rate as well as the high cost associated with drug development.

Quantification of sterol-specific response in human macrophages using automated imaged-based analysis

BACKGROUND

The transformation of normal macrophage cells into lipid-laden foam cells is an important step in the progression of atherosclerosis. One major contributor to foam cell formation in vivo is the intracellular accumulation of cholesterol.

METHODS

Here, we report the effects of various combinations of low-density lipoprotein, sterols, lipids and other factors on human macrophages, using an automated image analysis program to quantitatively compare single cell properties, such as cell size and lipid content, in different conditions.

RESULTS

We observed that the addition of cholesterol caused an increase in average cell lipid content across a range of conditions. All of the sterol-lipid mixtures examined were capable of inducing increases in average cell lipid content, with variations in the distribution of the response, in cytotoxicity and in how the sterol-lipid combination interacted with other activating factors. For example, cholesterol and lipopolysaccharide acted synergistically to increase cell lipid content while also increasing cell survival compared with the addition of lipopolysaccharide alone. Additionally, ergosterol and cholesteryl hemisuccinate caused similar increases in lipid content but also exhibited considerably greater cytotoxicity than cholesterol.

CONCLUSIONS

The use of automated image analysis enables us to assess not only changes in average cell size and content, but also to rapidly and automatically compare population distributions based on simple fluorescence images. Our observations add to increasing understanding of the complex and multifactorial nature of foam-cell formation and provide a novel approach to assessing the heterogeneity of macrophage response to a variety of factors.

Nanotopographic Regulation of Human Mesenchymal Stem Cell Osteogenesis

Mesenchymal stem cell (MSC) differentiation can be manipulated by nanotopographic interface providing a unique strategy to engineering stem cell therapy and circumventing complex cellular reprogramming. However, our understanding of the nanotopographic-mechanosensitive properties of MSCs and the underlying biophysical linkage of the nanotopography-engineered stem cell to directed commitment remains elusive. Here, we show that osteogenic differentiation of human MSCs (hMSCs) can be largely promoted using our nanoengineered topographic glass substrates in the absence of dexamethasone, a key exogenous factor for osteogenesis induction. We demonstrate that hMSCs sense and respond to surface nanotopography, through modulation of adhesion, cytoskeleton tension, and nuclear activation of TAZ (transcriptional coactivator with PDZ-binding motif), a transcriptional modulator of hMSCs. Our findings demonstrate the potential of nanotopographic surfaces as noninvasive tools to advance cell-based therapies for bone engineering and highlight the origin of biophysical response of hMSC to nanotopography.