Mechanisms of recovery from mechanical injury of cultured rat hepatocytes

Mechanical force and tensile strain activated hepatic stellate cells and inhibited retinol metabolism

OBJECTIVES

Hepatic stellate cells (HSCs), the principal producers of extracellular matrix proteins, play a major role in the development of liver fibrosis which is accompanied with elevated sinusoidal pressure and portal hypertension. We have isolated primary rat HSCs and investigated the effect of mechanical pressure and tensile strain on retinol metabolism in the cells.

RESULTS

Mechanical force and tensile strain significantly increased the expression of α-smooth muscle actin (α-SMA) and collagen I, and notably inhibited the expression of cellular retinol-binding protein I (CRBP-I), lecithin-retinol acyltransferase (LRAT), retinyl ester hydrolase (REH), retinoic acid receptor-β (RAR-β) and retinoid X receptor-α (RXR-α). Such effects were partially reversed by the retinoid X receptor antagonist, HX531, and the retinoic acid receptor antagonist, LE135.

CONCLUSION

Mechanical force and tensile strain significantly activate HSCs by regulating the retinoid metabolic pathway. Activation of HSCs can therefore be manipulated through mechanical force and tensile strain in vitro.

Module-based multiscale simulation of angiogenesis in skeletal muscle

Background

Mathematical modeling of angiogenesis has been gaining momentum as a means to shed new light on the biological complexity underlying blood vessel growth. A variety of computational models have been developed, each focusing on different aspects of the angiogenesis process and occurring at different biological scales, ranging from the molecular to the tissue levels. Integration of models at different scales is a challenging and currently unsolved problem.

Results

We present an object-oriented module-based computational integration strategy to build a multiscale model of angiogenesis that links currently available models. As an example case, we use this approach to integrate modules representing microvascular blood flow, oxygen transport, vascular endothelial growth factor transport and endothelial cell behavior (sensing, migration and proliferation). Modeling methodologies in these modules include algebraic equations, partial differential equations and agent-based models with complex logical rules. We apply this integrated model to simulate exercise-induced angiogenesis in skeletal muscle. The simulation results compare capillary growth patterns between different exercise conditions for a single bout of exercise. Results demonstrate how the computational infrastructure can effectively integrate multiple modules by coordinating their connectivity and data exchange. Model parameterization offers simulation flexibility and a platform for performing sensitivity analysis.

Conclusions

This systems biology strategy can be applied to larger scale integration of computational models of angiogenesis in skeletal muscle, or other complex processes in other tissues under physiological and pathological conditions.

Insulin, not leptin, promotes in vitro cell migration to heal monolayer wounds in human corneal epithelium

PURPOSE

To investigate the effects of insulin and leptin on in vitro wound healing of transformed human corneal epithelial cell monolayers and to identify cellular (migration versus proliferation) and intracellular signaling mechanisms.

METHODS

Scratch wounds were created in monolayers of an immortalized human corneal epithelial cell (HCEC) line. The wounded monolayers were exposed to insulin and leptin. Wound areas were measured every hour after wounding for up to 8 hours. Phosphoinositide 3-kinase (PI3-kinase) and mitogen-activated protein (MAP)-kinase signaling was analyzed with Western blot. The actions of insulin were also examined after incubation with inhibitors to extracellular signal regulated kinase (ERK 1/2) and PI3-kinase.

RESULTS

The presence of insulin, but not leptin facilitated closure of wounds created in corneal epithelial cell monolayers. Phosphorylation of ERK 1/2 and Akt was stimulated after exposure of the monolayers to insulin. Inhibitors of PI3-kinase and ERK 1/2 prevented or reduced insulin-induced corneal wound healing, respectively.

CONCLUSIONS

Exposure of corneal epithelium to insulin facilitated closure of in vitro small wounds through enhanced cell migration instead of proliferation, which depended on ERK 1/2 and PI3-kinase signaling. These data suggest a mechanism by which insulin may influence corneal wound healing in vitro. In vivo, disruptions to the insulin signaling pathway observed in diseases such as diabetes might account for the delayed wound healing and corneal defects.

Modeling of Oxygen Diffusion from the Blood Vessels to Intracellular Organelles

We describe recent models of oxygen transport in tissue along the pathway from the hemoglobin molecule to the mitochondria and illustrate their applications. Microvasculature is the major site of exchange between blood and parenchymal cells for gases (O2, CO2, CO, NO), nutrients, metabolic products, and drugs. These exchange processes are affected by the architecture of the microvessels and the surrounding cells; distribution of blood flow; transport characteristics of blood, cells, and interstitial space; and rates of various chemical reactions associated with the transport processes. These processes operate at multiple levels of biological organization, from the molecular to the organ levels. Quantitative understanding of molecular transport in cells and tissues, specifically of oxygen transport, is the prerequisite for understanding the mechanisms of many diseases and for designing effective therapies. Mathematical and computational models provide a powerful set of tools for studies of these complex phenomena.