title: The role of long-term label-retaining cells in the regeneration of adult mouse kidney after ischemia/reperfusion injury.
abstract: BACKGROUND
  Label-retaining cells (LRCs) have been recognized as rare stem and progenitor-like cells, but their complex biological features in renal repair at the cellular level have never been reported. This study was conducted to evaluate whether LRCs in kidney are indeed renal stem/progenitor cells and to delineate their potential role in kidney regeneration.
  
  
  METHODS
  We utilized a long-term pulse chase of 5-bromo-2'-deoxyuridine (BrdU)-labeled cells in C57BL/6J mice to identify renal LRCs. We tracked the precise morphological characteristics and locations of BrdU(+)LRCs by both immunohistochemistry and immunofluorescence. To examine whether these BrdU(+)LRCs contribute to the repair of acute kidney injury, we analyzed biological characteristics of BrdU(+)LRCs in mice after ischemia/reperfusion (I/R) injury.
  
  
  RESULTS
  The findings revealed that the nuclei of BrdU(+) LRCs exhibited different morphological characteristics in normal adult kidneys, including nuclei in pairs or scattered, fragmented or intact, strongly or weakly positive. Only 24.3 ± 1.5 % of BrdU(+) LRCs co-expressed with Ki67 and 9.1 ± 1.4 % of BrdU(+) LRCs were positive for TUNEL following renal I/R injury. Interestingly, we found that newly regenerated cells formed a niche-like structure and LRCs in pairs tended to locate in this structure, but the number of those LRCs was very low. We found a few scattered LRCs co-expressed Lotus tetragonolobus agglutinin (LTA) in the early phase of injury, suggesting differentiation of those LRCs in mouse kidney.
  
  
  CONCLUSIONS
  Our findings suggest that LRCs are not a simple type of slow-cycling cells in adult kidneys, indicating a limited role of these cells in the regeneration of I/R injured kidney. Thus, LRCs cannot reliably be considered stem/progenitor cells in the regeneration of adult mouse kidney. When researchers use this technique to study the cellular basis of renal repair, these complex features of renal LRCs and the purity of real stem cells among renal LRCs should be considered.
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Xiangchun
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China. haiyingl@sdu.edu.cn.
authors.forename: Haiying
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Lina
authors.initials: L
authors.lastname: Sun
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Zhixin
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Huibin
authors.initials: H
authors.lastname: Nie
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Aili
authors.initials: A
authors.lastname: Sun
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China.
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Nephrology, The Second Hospital of Shandong University,Shandong University, Jinan, PR. China. guanguangju@163.com.
authors.forename: Guangju
authors.initials: G
authors.lastname: Guan
mesh_terms: D000818:Animals; D017209:Apoptosis; D001973:Bromodeoxyuridine; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure*; D049109:Cell Proliferation; D002470:Cell Survival; D058948:Cell Tracking; D004847:Epithelial Cells / Q000166:cytology* / Q000378:metabolism; D015870:Gene Expression; D020287:In Situ Nick-End Labeling; D019394:Ki-67 Antigen / Q000235:genetics / Q000378:metabolism; D007668:Kidney; D037102:Lectins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012038:Regeneration / Q000502:physiology*; D015427:Reperfusion Injury / Q000235:genetics / Q000378:metabolism / Q000473:pathology*
chemical_list: D019394:Ki-67 Antigen; D037102:Lectins; C498355:Mki67 protein, mouse; C027112:fucose-binding lectin; D001973:Bromodeoxyuridine
keywords: AKI; Ischemia/reperfusion injury; Kidney regeneration; Label-retaining cells; Renal progenitor cells; Renal stem cells