Cell Adhesion Strength is Reduced by the Presence of Pericellular Matrix Patches

We present a detailed characterization of the organization of hyaluronan and bottlebrush proteoglycans in the pericellular matrix (PCM) of rat chondrocyte cells (RCJ-P) and PC3 prostrate cancer cells, and then use that insight to understand how the PCM impacts the transport of nanoparticles and charged molecules to the cell surface, and the cell's adhesion to substrates. Our studies reveal that the PCM strongly impacts the flux of nanoparticles to the cell surface in a size-dependent fashion. Further, the concentration of bottlebrushes (e.g. aggrecan, versican) in the PCM determines a maximal particle size that can reach the cell surface, ∼400nm for both cell lines but only ∼200nm when the PCM is saturated with proteoglycans. These observations have direct implications for studies of drug delivery vehicles and exosomes, whose particle sizes fall in this range. Our studies also provide evidence that negatively-charged chondroitin sulfates in the bottlebrush proteoglycans are available for binding to positively-charged molecules (e.g. growth factors), sequestering and concentrating molecules near the cell surface, as well as protecting them from enzymatic degradation. Super-resolution imaging of PCM at the cell-substrate interface reveals patches of PCM in co-existence with vinculin-rich adhesions. In order to address whether the PCM acts as a repulsive cushion, we quantify the cell adhesion strength versus enzymatic degradation of the PCM using a spinning disk apparatus. The studies show that the adhesion strength increases by ∼24% for RCJP cells enzymatically-treated with hyaluronidase and by a factor of ∼39% for PC3 cells. A similar increase in adhesion occurs with chondroitinase-ABC treatment. Together, these quantitative measurements of the pericellular matrix indicate that this common but neglected in vitro and in vivo structure deserves further attention to understand how it regulates cells’ interactions with their surroundings. Funding: NSF CAREER-DMR-0848797.