Mesangial homeostasis and pathobiology: their role in health and disease.

Mesangial homeostasis is an integral component of normal glomerular function. Alterations in mesangial homeostasis occur frequently, not only in primary glomerular disorders, but also in association with primary tubular interstitial and vascular pathology, although generally the disturbances are not as marked in the latter situations. Mesangial changes could be transitory and reversible or permanent and irreversible, depending on the type and degree of damage inflicted and the reparative ability of the mesangium at a given time. Understanding mesangial pathobiology is crucial for comprehending the reactive and pathological processes that occur in glomeruli. The mesangium is usually the first to react to injurious glomerular events and is often the last to return to normal after the pathological insult has ceased and repair mechanisms have been activated. This is obvious in renal biopsy specimens where mesangial hypercellularity and/or matrix expansion are very common findings in primary glomerular disorders and, as a reactive phenomenon, in primary interstitial and vascular diseases. Repairing mesangial damage represents a fundamental process needed for restoring glomerular function. Since a component of the mesangial damage frequently includes the loss of mesangial cells, a way to revamp mesangial cellularity is essential for restoring mesangial homeostasis. This fact should be taken into account when designing therapies aimed at restoring mesangial integrity and homeostasis.