Claudins 6, 9, and 13 are developmentally expressed renal tight junction proteins.
The adult proximal tubule is a low-resistance epithelium where there are high rates of both active transcellular and passive paracellular NaCl transport. We have previously demonstrated that the neonatal rabbit and rat proximal tubule have substantively different passive paracellular transport properties than the adult proximal tubule, which results in a maturational change in the paracellular passive flux of ions. Neonatal proximal tubules have a higher P(Na)/P(Cl) ratio and lower chloride and bicarbonate permeabilities than adult proximal tubules. Claudins are a large family of proteins which are the gate keepers of the paracellular pathway, and claudin isoform expression determines the permeability characteristics of the paracellular pathway. Previous studies have shown that claudins 1, 2, 3, 4, 5, 7, 8, 10, 11, 12, 15, and 16 are expressed in the adult mouse kidney. To determine whether there are developmental claudin isoforms, we compared the claudin isoforms present in the neonatal and adult kidney using RT-PCR to detect mRNA of claudin isoforms. Claudin 6, claudin 9, and claudin 13 were either not expressed or barely detectable in the adult mouse kidney using traditional PCR, but were expressed in the neonatal mouse kidney. Using real-time RT-PCR, we were able to detect a low level of claudin 6 mRNA expression in the adult kidney compared with the neonate, but claudin 9 and claudin 13 were only detected in the neonatal kidney. There was the same maturational decrease in these claudin proteins with Western blot analysis. Immunohistochemistry showed high levels of expression of claudin 6 in neonatal proximal tubules, thick ascending limb, distal convoluted tubules, and collecting ducts in a paracellular distribution but there was no expression of claudin 6 in the adult kidney. Using real-time RT-PCR claudin 6 and 9 mRNA were present in 1-day-old proximal convoluted tubules and were virtually undetectable in proximal convoluted tubules from adults. Claudin 13 was not detectable in neonatal or adult proximal convoluted tubules. In summary, we have identified developmentally expressed claudin isoforms, claudin 6, claudin 9, and claudin 13. These paracellular proteins may play a role in the maturational changes in paracellular permeability.
Abuazza
Ghazala
G
Deptartment of Pediatrics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-9063, USA.
Becker
Amy
A
Williams
Scott S
SS
Chakravarty
Sumana
S
Truong
Hoang-Trang
HT
Lin
Fangming
F
Baum
Michel
M
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D057167:Claudins; D005260:Female; D018507:Gene Expression Regulation, Developmental; D007536:Isomerism; D007668:Kidney / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000502:physiology; D007686:Kidney Tubules, Distal / Q000502:physiology; D007687:Kidney Tubules, Proximal / Q000502:physiology; D008138:Loop of Henle / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D011247:Pregnancy; D012333:RNA, Messenger / Q000378:metabolism; D019108:Tight Junctions / Q000502:physiology*
D057167:Claudins; C515809:Cldn13 protein, mouse; C515808:Cldn9 protein, mouse; D008565:Membrane Proteins; D012333:RNA, Messenger; C122101:claudin 6