Human Nephrogenesis can Persist Beyond 40 Postnatal Days in Preterm Infants.

Human nephrogenesis is typically completed by 36 weeks gestation; however, it is impacted by preterm birth. Early studies suggested that nephrogenesis persisted for ≤40 postnatal days in preterm infants. However, the postmenstrual age (PMA) of the preterm infants who survived >40 days was uncertain. In this study, we sought to reexamine postnatal kidney development in preterm infants surviving >40 days. Human kidney samples were obtained from an institutional biobank. Samples were considered controls if survival was ≤4 days after birth with PMA of 30 to ≤36 weeks. Kidneys from preterm neonates with postnatal survival >40 days and PMA of 30 to ≤36 weeks were compared to controls. We counted glomerular generations, measured nephrogenic zone widths (NZW), and performed immunofluorescence (IF) with SIX1 and RET. We compared kidney weights and quantified the cross-sectional area of proximal (lotus tetragonolobus lectin [LTL], SL22A2), distal (SLC12A3, KCNJ10), and glomerular (nephrin) markers using IF. Seven preterm infants surviving >40 days and 8 controls were analyzed. Four of 7 preterm infants had histologic and molecular evidence of nephrogenesis. Cessation of nephrogenesis in preterm infants occurred 2 weeks earlier than PMA-matched controls with attenuated expression of both SIX1 and RET. We found increased kidney weight-to-body weight ratio, increased distal tubular cross-sectional staining in the superficial nephrons, and distal tubular hypertrophy and hyperplasia in the preterm infant kidneys. Our study supports that nephrogenesis in preterm infants persists longer than previously thought with evidence of early nephron stress, placing importance on the neonatal environment.