Proximal Tubular Development Is Impaired with Downregulation of MAPK/ERK Signaling, HIF-1α, and Catalase by Hyperoxia Exposure in Neonatal Rats

Abstract

Supplemental oxygen therapy (hyperoxia) is a widely used treatment for alveolar hypoxia in preterm infants. Despite being closely monitored, hyperoxia exposure is believed to undermine neonatal nephrogenesis and renal function caused by elevated oxidative stress. Previous studies have mostly focused on the hyperoxia-induced impairment of glomerular development, while the long-term impact of neonatal hyperoxia on tubular development and the regulatory component involved in this process remain to be clarified. Here, we examined tubular histology and apoptosis, along with the expression profile of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling, hypoxia-inducible factor 1α (HIF-1α), and catalase, following hyperoxia exposure in neonatal rats. Hematoxylin and eosin (H&E) staining revealed the early disappearance of the nephrogenic zone, as well as dilated lumens and reduced epithelial cells, of mature proximal tubules following neonatal hyperoxia. A robust increase in tubular cell apoptosis caused by neonatal hyperoxia was found using a TUNEL assay. Moreover, neonatal hyperoxia altered renal MAPK/ERK signaling activity and downregulated the expression of HIF-1α and catalase in the proximal tubules throughout nephrogenesis from S-shaped bodies to mature proximal tubules. Cell apoptosis in the proximal tubules was positively correlated with HIF-1α expression on the 14th postnatal day. Our data indicates that proximal tubular development is impaired by neonatal hyperoxia, which is accompanied by altered MAPK/ERK signaling as well as downregulated HIF-1α and catalase. Therapeutic management that targets MAPK/ERK signaling, HIF-1α, or catalase may serve as a protective agent against hyperoxia-induced oxidative damage to neonatal proximal tubules.

TUNEL Assay: A Powerful Tool for Kidney Injury Evaluation

“…Mixed acute-and-chronic injury, where toxic exposures, disease states, and/or assessments were both acute (i.e., hours, days) and chronic (i.e., weeks, months, years) in the same study, were observed in human transplant rejection (biopsy 1 week to 3 years post-transplant) [ 88 ], swine hepatitis E virus infection (7 and 14 days post-inoculation) [ 52 ], CO 2 pneumoperitoneum-induced stress in hydronephrotic kidneys (2 weeks hydronephrosis, 2 days post-pneumoperitoneum) [ 53 ], mesangial proliferative glomerulonephritis induced by snake venom (1 to 14 days post-injection) [ 99 ], unilateral ureteral obstruction (1 to 14 days of obstruction) [ 100 ], uranyl acetate exposure (1 to 28 days of exposure) [ 101 ], aristocholic acid nephropathy (5 and 30-day daily exposure) [ 102 ], and neonatal hyperoxia (tested 1 to 60 postnatal days, exposed to hyperoxia first 14 days) [ 103 ]. Fourteen days after impact is a very common assessment time point for these kinds of kidney injuries [ 52 , 53 , 99 , 101 , 103 ]. In the majority of cases, TUNEL-positive cells were localized in tubules and collective ducts.…”

“…Inflammation was identified by IHC of tumor necrosis factor alpha (TNFα) [ 134 ]; tumor growth factors TGFβ [ 66 ] and TGF-β1 [ 135 ]; serine/threonine kinase 1 (SGK1) [ 135 ]; electron-transfer flavoprotein, beta-subunit (ETFβ) [ 136 ]; Janus kinase-2 (JAK2) [ 137 ]; signal transducer and activator of transcription 3 (STAT3) [ 137 ]; nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) [ 137 ] and its inhibitor protein IκB [ 137 ]. For kidney injury assessment, kidney injury molecule-1 (KIM-1) [ 24 ], aquaporin-1 channel (AQP-1) [ 45 ], hypoxia-inducible factor 1-alpha transcription factor (HIF-1α) [ 103 ], Asc-type amino acid transporter-1 (Asc-1) [ 121 ], mammalian target of rapamycin (mTOR) [ 131 ] kinase, and transglutaminase II [ 89 ] were used. Oxidative kidney injury was studied using markers such as 8-hydroxyguanosine (8OHdG) [ 102 ], neutrophil gelatinase-associated lipocalin (NGAL) [ 102 ], NAD-dependent deacetylase sirtuin-1 (SIRT1) [ 138 ], and heme oxygenase 1 (HO-1) [ 90 ].…”

Association of Nuclear Receptor Coactivators with Hypoxia-Inducible Factor-1α in the Serum of Patients with Chronic Kidney Disease

“…However, currently, the effects of HIF and vascular endothelial growth factor (VEGF) are not well known. Some studies on renal diseases found that HIF-1α played a protective role [13][14][15], but others reported that it was a risk factor [16][17][18]. Current evidence indicated that HIF-1α could be regulated by some NR [19][20][21]; however, there was no report showing the relationship between NCOAs and HIF-1α.…”

Neonatal Hyperoxia Downregulates Claudin-4, Occludin, and ZO-1 Expression in Rat Kidney Accompanied by Impaired Proximal Tubular Development

“…Supplemental oxygen therapy (hyperoxia) is commonly administered in the management of premature infants with respiratory disorders [ 1 , 2 ]. Nonetheless, increasing evidence from various clinical and experimental observations suggests that neonatal hyperoxia may cause oxidative damage and adversely affects glomerular and tubular maturity [ 3 , 4 ]. These adverse effects are manifested by enlarged renal corpuscles, renal tubular injuries, and interstitial inflammation during the perinatal period, which might extend into adulthood and influence renal function [ 5 , 6 ].…”