In vitro muscle model studies

Abstract

Studies of soft tissues under mechanical loading have shown that skeletal muscle tissue is highly susceptible to sustained compression, eventually leading to tissue breakdown in the form of deep pressure ulcers [1, 21. This breakdown starts at the cellular level with disintegration of contractile proteins and damage to the cell membrane and nucleus, followed by inflammatory reactions. Although it is clear that both the duration and magnitude of compression affect muscle cell damage, the aetiological pathways whereby tissue compression leads to cell damage are not completely understood. To date, theories have mainly focussed on the impairment of metabolite and oxygen transport through the tissue [24j, whereas the direct damaging effects of cell deformation due to compressive straining have only recently been identified as a cause of deep pressure ulcer development [5j. Most probably the aetiology is multifactorial in nature and both processes play a role. Tissue compression may (partially) occlude blood vessels and the smaller capillaries, which then no longer provide enough oxygen to the tissue, resulting in local ischaemia. Due to the impaired tissue perfusion, transport of nutrients and waste products to and from the metabolically active muscle cells is affected, while closure of the lymphatic system may result in additional transport problems, as waste products, excess fluids and proteins are no longer properly removed from the tissue. The restoration of transport during tissue reperfusion can be extremely harmful because of reactive oxygen species accumulating in the tissue upon load removal. Cell deformation, on the other hand, triggers a variety of effects such as altered membrane stresses, volume changes and cytoskeletal reorganisation, which may be involved in early cell damage. It has been shown that the response of muscle cells to deformation during tensile or shear straining is crucial to cellular degeneration or adaptation [6, 7j, and a comparable response might be expected for compressive straining. As it is impossible to study the effects of reduced transport and cell deformation independently of each other and other predisposing factors in human studies, these aspects should be studied using model systems. Ideally, a hierarchy of model systems ranging from single-cell in-vitro models to animal models (Chap. 12) and human studies should provide informa tion about the relative contribution of, for example, cell deformation, local ischaemia, and reperfusion in the aetiology of pressure ulcers. This chapter reviews the use of in-vitro models of muscle cells and muscle tissue to study the aetiology of deep pressure ulcers. In general, in-vitro models offer better experimental control and fewer ethical considerations than in-vivo (animal) studies. Literally, in vitro means in glass and these model systems are defined as cells or tissues cultured in the laboratory under artificial conditions, outside the human body. One of the benefits of in-vitro cell culture is the fact that the same cell clone or cell line can be used in different studies and in different laboratories to improve reproducibility of results. Moreover, the same cell line can be used when creating muscle models using the concept of tissue engineering.