Description
Cystatin C or cystatin 3 (other names: gamma trace, post-gamma-globulin or neuroendocrine basic polypeptide) is a protein encoded by the CST3 gene and is synthesized in various levels by different cell-types and appears in most body fluids.
Cystatins belong to a superfamily of cysteine proteases inhibitors such as papain and Cathepsins B, H, K, L, and S. They have been found in both plants and animals.
Cystatin C, with molecular weight of 13 260 Da and composed of 120 amino acids, lacks carbohydrate and contains two disulfide bridges located near the carboxyl terminus. Cysteine proteases play an important role in protein degradation (e.g. of photoreceptor outer segments in the retinal pigment epithelium) and the balance between these proteases and their specific inhibitors is therefore of great interest.
Cystatin C level is increased in patients with malignant diseases, rheumatic diseases and related to the insufficiency of renal function. This protein appears to be a better marker than creatine. It may be especially useful in those cases where the creatinine measurement is not appropriate: for instance in liver cirrhosis, in obese, in malnourished or in patients with reduced muscle mass, too. Cystatin C measurement may be useful in the early detection of kidney disease when other parameters might still be normal. In addition to kidney dysfunction; it has been associated with an increased risk of cardiovascular disease and heart failure in older adults.
Low levels of cystatin C indicate the breakdown of the elastic laminae and, subsequently, the atherosclerosis and abdominal aortic aneurysm. The blood level of cystatin C predicts survival after one type of heart attack. On the other hand, a high level of cystatin C in the blood after a heart attack is an ominous sign because it reflects the failure of kidney to clear cystatin C from the blood into the urine. Moreover cystatin C levels are correlating with levels of triglycerides, LDL-cholesterol, BMI and the age.
Cystatin C was identified, quantitated, and localized in mouse, rat, and human retinas. In the normal adult rat retina cystatin C is present at high concentrations as it is throughout its postnatal development. Its concentration increases to a peak at the time when rat pups open their eyes and remains at a high level. It is mainly localized to the pigment epithelium, but also to some few neurons of varying types in the inner retina. Cystatin C is similarly expressed in normal mouse and human retinas