In vitro formation and expansion of cysts derived from human renal cortex epithelial cells

In vitro formation and expansion of cysts derived from human renal cortex epithelial cells. Acquired renal cysts derive from terminally differentiated tubular epithelium in adults as a consequence of increased epithelial cell proliferation, fluid accumulation and extracellular matrix remodelling. To understand better how human epithelial cysts may be initiated and progressively expand, cells from primary cultures of normal human adult renal cortex were dispersed in polymerized type I collagen. The transparent matrix permitted repeated observation by light microscopy of cyst formation from individual renal cells. The cyst cells reacted strongly with distal nephron histochemical markers (cytokeratin antibodies AE1/AE3, epithelial membrane antigen, and Arachis hypogaea lectin) but inconsistently or not at all to markers of proximal tubules ( Tetragonolobus purpureas lectin and Phaseolus vulgaris erthroagglutinin lectin). The number of spherical, fluid-filled epithelial cysts that developed in a standardized microscope field quantified cyst initiation. Cyst progression was determined from the increase in the diameter (surface area) of cysts and represents a hyperplastic event. EGF or TGF α , were required in serum-free defined medium to cause cysts to develop from individual epithelial cells dispersed in the matrix; insulin was required as a co-factor. The EC 50 for EGF was approximately 0.1 ng/ml, and for insulin 1µg/ml. Early cultures of normal cortex formed cysts more efficiently when dispersed in collagen matrix than cells passaged several times before suspension in the gel. Agonists of adenylate cyclase (PGE 1 , AVP, VIP, PTH, forskolin, cholera toxin), methylisobutylxanthine, and 8-Br-cAMP, though incapable of causing cyst formation alone in defined medium, enhanced cyst initiation and progression in the presence of EGF and insulin. Angiotensin II, TNF α , β-estradiol, and pertussis toxin had no effect in the absence or presence of EGF and insulin. Pertussis toxin inhibited cyst initiation and expansion caused by EGF and forskolin but potentiated cyst initiation and expansion caused by EGF and PGE 1 . Cyst formation and expansion were inhibited by TGF β1 , and 2-chloroadenosine. Polarized monolayers of human renal cortical cells grown on permeable membranes were used to independently quantify the effects of agonists on the net secretion of solute and water from the basolateral to the apical surface of the cells. PGE 1 , forskolin, and 8-Br-cAMP stimulated net fluid secretion that was sustained for several days; EGF enhanced forskolin-stimulated fluid secretion. We conclude that the formation and expansion of in vitro cysts derived from solitary human cortex cells depends on the coordinated interplay between cellular proliferation and fluid secretion. The initiation of cyst formation from solitary epithelial cells is determined primarily by EGF or TGF α (cyclic AMP has a secondary role), whereas the rate of fluid accumulation is controlled by cyclic AMP (EGF or TGF α have secondary roles). These experiments support the view that renal cyst formation and growth may be regulated by endocrine, autocrine and paracrine factors.