HYALURONAN IS THE ORGANIZATIONAL SCAFFOLD OF THE INTERPHOTORECEPTOR MATRIX OF THE RETINA

Abstract

We have established the distribution of hyaluronan (HA) in the interphotoreceptor matrix (IPM) of the retina, and demonstrated its interaction with novel molecules present in this compartment. HA localization was defined with biotinylated hyaluronan binding complex, (bHABC). SPACR, a sialoglycoprotein, and SPACRCAN, a proteoglycan, are novel molecules localized in the 1PM with polyclonal antibodies prepared against their human antigens. SPACR-HA and SPACRCAN-HA interactions were documented in precipitation experiments on BPM extracts using cetylpyridinium chloride (CPC) in conjunction with Streptomyces hyaluronidase digestion. In tissue sections of human retina, bHABC heavily decorates HA in the matrix surrounding rods, with lighter binding of the cone associated matrix. SPACR and SPACRCAN immunoreactivity is prominent surrounding rods and cones. HA, SPACR and SPACRCAN are isolated as an aqueous insoluble IPM complex. CPC co-precipitates SPACR, SPACRCAN and HA from an undigested extract of IPM, but neither SPACR nor SPACRCAN precipitate with CPC when the extract is first digested with Streptomyces hyaluronidase. The deduced AA-sequence of SPACR and SPACRCAN contain HA binding motifs of the RHAMM type. The precipitation studies suggest that these HA binding motifs are functional. The implication from these studies is that HA serves as the primary scaffold to which SPACR, SPACRCAN and other IPM molecules form associative interactions in the DPM.