Small leucine-rich proteoglycans orchestrate receptor crosstalk during inflammation

Inflammation is not only a defensive mechanism against microbial invasion, but also frequently represents a critical response to tissue injury under sterile conditions. It is now well established that tissue injury leads to the release of endogenous molecules of intra- and extracellular origin acting as damage-associated molecular patterns (DAMPs). The small leucine-rich proteoglycans (SLRPs) can act as powerful DAMPs following their proteolytical release from the extracellular matrix. Recent investigations of SLRP signaling networks revealed new levels of complexity, showing that SLRPs can cluster different types of receptors and orchestrate a host of downstream signaling events. This review will summarize the evidence for the multifunctional proinflammatory signaling properties of the two archetypal SLRPs, biglycan and decorin. These secreted proteoglycans link the innate to the adaptive immune response and operate in a broad biological context, encompassing microbial defense, tumor growth and autoimmunity.