Plasticity of mesangial cells: a basis for understanding pathological alterations.

In the last two decades, the ability of mesangial cells to respond to various stimuli or injurious agents by altering their phenotype and function has become recognized. The plasticity of these mesangial cells has been linked to the morphological and functional alterations responsible for the pathologic findings. Many of the glomerular disorders target the mesangium as the primary and/or initial site of injury. Understanding how mesangial cells are altered in the various conditions provides a platform for conceptualizing pathologic mechanisms and defining key steps amenable to therapeutic intervention. The present paper reviews the normal and altered mesangium with an emphasis on mechanisms involved in alterations of mesangial homeostasis. Mesangial cells and matrix are very important in maintaining normal glomerular structure, and function and the plasticity of these cells is responsible for pathological manifestations, repair, and scarring. Our more sophisticated understanding of mesangial cell behavior and matrix biology provides very useful information to help design new therapeutic approaches to the treatment of renal diseases. The potential for bone marrow-derived cells to differentiate into mesangial cells and repopulate damaged mesangium, thus "healing" what is today considered to be irreversible damage represents an exciting new area of research.