Kidney Cyst Epithelia in Tuberous Sclerosis Complex (TSC) Exhibit Propagation and Expansion of A-Intercalated, but Loss of B-Intercalated and Principal Cells: The Role of FOXI1, FOXP1, and DMRT2 Transcription Factors.

Kidney cystic epithelium primarily comprises proliferating A-intercalated (A-IC) cells in humans and mouse models of TSC. These studies explored the expression of transcription factors (TF) that drive the development of A-IC cells and the downregulation of B-intercalated (B-IC) cells, as well as the status and localization of Tsc1 and Tsc2 in epithelial cells lining the cysts. Transcriptome studies indicated enhanced expression of the following TFs: DMRT2, FOXI1, and FOXP1 in young TSC mice, and DMRT2 and FOXI1 in aged mice. The expression of Hmx2 decreased in TSC mice of all ages. Our studies further demonstrated: (1) distinct and predominant DMRT2 and FOXP1 localization in the cystic epithelium of in TSC mouse models; and (2) expression of Foxi1, Tsc1, and Tsc2 in epithelial cells lining the kidney cysts. Expression of DMRT2, FOXI1, and FOXP1 is enhanced in the A-IC cells lining the kidney cysts of TSC mouse models. In the same models, the expression of Hmx2 mRNA is decreased and is accompanied by the loss of B-IC cells in cyst epithelia. Both DMRT2 and FOXP1 localized to the nucleus of A-IC cells of the renal cysts, suggesting that TSC kidney cystogenesis is driven by factors that exclusively promote A-IC expansion.