title: Glomerular parietal epithelial cells in kidney physiology, pathology, and repair.
abstract: OBJECTIVE
  We have summarized recently published glomerular parietal epithelial cell (PEC) research, focusing on their roles in glomerular development and physiology, and in certain glomerular diseases. The rationale is that PECs have been largely ignored until the recent availability of cell lineage tracing studies, human and murine PEC culture systems, and potential therapeutic interventions of PECs.
  
  
  RESULTS
  Several new paradigms involving PECs have emerged demonstrating their significant contribution to glomerular physiology and numerous glomerular diseases. A subset of PECs serving as podocyte progenitors have been identified in normal human glomeruli. They provide a source for podocytes in adolescent mice, and their numbers increase in states of podocyte depletion. PEC progenitor number is increased by retinoids and angiotensin-converting enzyme inhibition. However, dysregulated growth of PEC progenitors leads to pseudo-crescent and crescent formation. In focal segmental glomerulosclerosis, considered a podocyte disease, activated PECs increase extracellular matrix production, which leads to synechial attachment and, when they move to the glomerular tuft, to segmental glomerulosclerosis. Finally, PECs might be adversely affected in proteinuric states by undergoing apoptosis.
  
  
  CONCLUSIONS
  PECs play a critical role in glomerular repair through their progenitor function, but under certain circumstances paradoxically contribute to deterioration by augmenting scarring and crescent formation.
authors.affiliation: aDivision of Nephrology, University of Washington Medical Center, Seattle, Washington, USA bDivision of Nephrology, Medizinische Klinik und Poliklinik IV, Klinikum der Universität München-Innenstadt, Munich, Germany cExcellence Centre for Research, Transfer and High Education for the Development of De Novo Therapies (DENOTHE), University of Florence, Florence, Italy.
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Shankland
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Anders
authors.forename: Paola
authors.initials: P
authors.lastname: Romagnani
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D019070:Cell Lineage; D049109:Cell Proliferation; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D007674:Kidney Diseases / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D007678:Kidney Glomerulus / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D050199:Podocytes / Q000378:metabolism / Q000473:pathology; D012038:Regeneration; D013234:Stem Cells / Q000378:metabolism / Q000473:pathology*