Structural and cellular changes in fetal renal papilla during development

The mature renal papilla is characterized by medullary collecting ducts, Henle’s loops, vasa recta and the interstitium. Cortical and medullary stromal cells are essential for the regulation of urine concentration and other specialized kidney functions. Mechanisms that direct the renal papilla development are not clearly understood. In recent years, the renal papilla has been identified as a niche for renal stem/progenitor cells in the adult mouse. Studies on experimental animals evidenced a probably common interstitial progenitor for the medullary and cortical stromal cells, characterized by the Foxd1+/PAX2- phenotype. Moreover, Hox10 and Hox11 expression is required for differentiation and patterning of the multiple subtypes of developing medullary interstitial cells. Given the scarcity of morphological and molecular studies on the human renal papilla, this work aimed to evidence morphological changes during human gestation, both in the architecture of the medullary interstitium and in cell types differentiating between the collecting tubules and the Henle’s loops. Future immunohistochemical studies are needed to better identify different interstitial cell types giving rise to the mature interstitium of the renal papilla