Thomas Schmid, PhD, was the first scientist to discover lubricin in cartilage. He showed it to be synthesized by only the chondrocytes at the surface of articular cartilage (Schumacher et al., 1994) and not the deep zone chondrocytes, and called the molecule superficial zone protein (SZP). Later in 1999 it was shown by Gregory Jay that SZP is the same as or very closely related to the molecule lubricin. Schmid then showed that the cartilage derived molecule had lubrication properties like those of the synovial fluid-derived lubricin (Schmid et al., 2002). Schmid generated the first antibodies specific for lubricin and then a second generation of monoclonal antibodies specific for human lubricin (Su et al., 2001). He has worked on the structure and function of this interesting glycoprotein for 20 years. He has collaborated with Hari Reddi’s lab to show lubricin synthesis is stimulated by mechanical shear. This increase is due to at least in part to TGFb signaling (Neu et al., 2007). One of the most exciting observations from this collaboration shows cartilage damage in osteoarthritis is directly proportional to increases in the coefficient of friction for different cartilage regions (Neu et al., 2010) with a correlation coefficient of 0.999. Similarly the concentration of SZP extracted from these cartilage regions also correlated with cartilage damage (r2 = 0.82), therefore the measurement of SZP concentrations may have diagnostic or prognostic utility. At the very least lubricin is one of the most important macromolecules to study during the wear of cartilage for two reasons. One, it normally resides on the very surface of the articular cartilage interface. Two, it should be a protective molecule with respect to cartilage wear because it is the major macromolecular lubricant in the joint.
Schmid also has extensive expertise in collagen biochemistry, musculoskeletal cell biology, chondrocyte differentiation markers, chondrocyte hypertrophy and mineralization. The major theme of Schmid’s research has been the identification of molecular markers that help define the chondrocyte phenotype especially with respect to select regions of articular and growth plate cartilage. Schmid’s research has been supported by the NIH and the Arthritis Foundation.
