Disease expression in cultured pigment epithelium. Feline mucopolysaccharidosis VI

Primary cultures of retinal pigment epithelial (RPE) cells from cats with mucopolysaccharidosis VI (MPS VI) have been initiated from mixed populations of cells (ie, derived from the entire eyecup and represented by both pigmented and nonpigmented RPE cells). The cells were enzymatically dissociated from the eyecup and seeded at 6 X 10(4) cells/cm2. Cells from normal and affected cats formed confluent monolayers of polygonal cells between 5-10 days in culture and maintained most of their in vivo morphologic characteristics. The only abnormality observed in the MPS VI-affected cultures was the accumulation of vacuolated intracytoplasmic inclusions; when numerous, these vacuoles caused cellular hypertrophy. Hypertrophy was present only in cells devoid of pigment. Pigmented cells adjacent to or near the hypertrophied cells exhibited little or no accumulation of vacuoles. The inclusions were indistinguishable from those observed in vivo in terms of size, distribution, and appearance. The MPS VI-affected RPE exhibited deficient arylsulfatase B (ASB) activity (RPE-ASB activity: normal = 506 nmol/hr/mg protein; affected = 22 nmol/hr/mg protein), whereas the activities of two other lysosomal enzymes, arylsulfatase A and alpha-L-iduronidase, were normal. A method was developed to initiate primary cultures of RPE cells from defined regions of normal and MPS VI-affected eyes. Studies indicated that cultures initiated from superior-equatorial regions (RPE nonpigmented) contained more vacuolated cytoplasmic inclusion than those initiated from inferior-equatorial regions (RPE pigmented). These findings indicated that the spatial distribution characteristic of the disease in vivo was maintained in culture and that disease expression was inversely correlated with pigmentation.