title: Articular cartilage chondrocytes express aromatase and use enzymes involved in estrogen metabolism.
abstract: BACKGROUND
  Sex hormones, especially estrogens, have been implicated in articular cartilage metabolism and the pathogenesis of postmenopausal osteoarthritis. The conversion by aromatase (CYP19A1) of androstenedione into estrone (E1) and of testosterone into 17β-estradiol (E2) plays a key role in the endogenous synthesis of estrogens in tissue.
  
  
  METHODS
  We analyzed the expression of aromatase (CYP19A1) in immortalized C-28/I2 and T/C-28a2 chondrocytes, as well as in cultured primary human articular chondrocytes and human articular cartilage tissue, by means of RT-PCR, Western blotting and immunohistochemistry. By means of quantitative RT-PCR and enzyme-linked immunosorbent assay, we also determined whether the aromatase inhibitor letrozole influences estrogen metabolism of cultured chondrocytes in immortalized C-28/I2 chondrocytes.
  
  
  RESULTS
  Aromatase mRNA was detected in both immortalized chondrocyte cell lines, in cultured primary human chondrocytes, and in human articular cartilage tissue. By means of Western blot analysis, aromatase was detected at the protein level in articular cartilage taken from various patients of both sexes and different ages. Cultured primary human articular chondrocytes, C-28/I2 and T/C-28a2, and human articular cartilage tissue reacted with antibodies for aromatase. Incubation of C-28/I2 chondrocytes with 10⁻¹¹ M to 10⁻⁷M letrozole as an aromatase inhibitor revealed significantly increased amounts of the mRNAs of the enzyme cytochrome P4501A1 (CYP1A1), which is involved in the catagen estrogen metabolism, and of the estrogen receptors ER-α and ER-β. Concomitantly, synthesis of estrone (E1) was significantly downregulated after incubation with letrozole.
  
  
  CONCLUSIONS
  We demonstrate that human articular cartilage expresses aromatase at the mRNA and protein levels. Blocking of estrone synthesis by the aromatase inhibitor letrozole is counteracted by an increase in ER-α and ER-β. In addition, CYP1A1, an enzyme involved in catabolic estrogen metabolism, is upregulated. This suggests that articular chondrocytes use ERs functionally. The role of endogenous synthesized estrogens in articular cartilage health remains to be elucidated.
authors.forename: Martin
authors.initials: M
authors.lastname: Schicht
authors.forename: Jana
authors.initials: J
authors.lastname: Ernst
authors.forename: Andrea
authors.initials: A
authors.lastname: Nielitz
authors.forename: Lars
authors.initials: L
authors.lastname: Fester
authors.forename: Michael
authors.initials: M
authors.lastname: Tsokos
authors.forename: Saskia S
authors.initials: SS
authors.lastname: Guddat
authors.forename: Lars
authors.initials: L
authors.lastname: Bräuer
authors.forename: Judith
authors.initials: J
authors.lastname: Bechmann
authors.forename: Karl-Stefan
authors.initials: KS
authors.lastname: Delank
authors.forename: David
authors.initials: D
authors.lastname: Wohlrab
authors.forename: Friedrich
authors.initials: F
authors.lastname: Paulsen
authors.forename: Horst
authors.initials: H
authors.lastname: Claassen
mesh_terms: D000328:Adult; D000368:Aged; D001141:Aromatase / Q000096:biosynthesis*; D015153:Blotting, Western; D002358:Cartilage, Articular / Q000378:metabolism*; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D004967:Estrogens; D001141:Aromatase
references.citation: Anticancer Res. 2011 Dec;31(12):4369-86
references.pmid: 22199302
references.citation: Maturitas. 2010 Sep;67(1):29-33
references.pmid: 20537472
references.citation: Am J Physiol Endocrinol Metab. 2012 Jun 1;302(11):E1381-9
references.pmid: 22414805
references.citation: J Mol Endocrinol. 2001 Oct;27(2):249-53
references.pmid: 11564607
references.citation: Med Hypotheses. 2009 Jun;72(6):720-2
references.pmid: 19249162
references.citation: Calcif Tissue Int. 2012 Jul;91(1):59-68
references.pmid: 22644322
references.citation: J Clin Invest. 1994 Dec;94(6):2307-16
references.pmid: 7989586
references.citation: Methods Mol Med. 2004;100:23-36
references.pmid: 15280585
references.citation: Menopause. 2013 May;20(5):578-86
references.pmid: 23615651
references.citation: Life Sci. 1992;50(23):1737-44
references.pmid: 1598063
references.citation: Maturitas. 2000 Jun 30;35(3):183-99
references.pmid: 10936736
references.citation: Scand J Rheumatol. 1992;21(4):196-200
references.pmid: 1529287
references.citation: J Steroid Biochem Mol Biol. 2003 Sep;86(3-5):225-30
references.pmid: 14623515
references.citation: J Endocrinol. 2004 Jul;182(1):165-72
references.pmid: 15225141
references.citation: J Mammary Gland Biol Neoplasia. 2000 Jul;5(3):251-8
references.pmid: 14973387
references.citation: Clin Rheumatol. 1991 Sep;10(3):316-9
references.pmid: 1838722
references.citation: Pak J Pharm Sci. 2011 Apr;24(2):217-9
references.pmid: 21454173
references.citation: Arthritis Rheum. 2003 Dec;48(12):3395-403
references.pmid: 14673991
references.citation: J Endocrinol. 2006 Feb;188(2):193-203
references.pmid: 16461546
references.citation: Osteoporos Int. 2011 May;22(5):1573-9
references.pmid: 20652228
references.citation: J Steroid Biochem Mol Biol. 2013 Mar;134:15-22
references.pmid: 23085002
references.citation: Horm Res. 2009 Apr;71 Suppl 2:41-7
references.pmid: 19407496
references.citation: J Bone Miner Res. 1997 Sep;12(9):1416-23
references.pmid: 9286757
references.citation: Acta Paediatr. 2007 Sep;96(9):1275-9
references.pmid: 17718780
references.citation: Am J Physiol Endocrinol Metab. 2007 Jul;293(1):E410-5
references.pmid: 17473054
references.citation: Ann Rheum Dis. 1989 Jun;48(6):523-7
references.pmid: 2662920
references.citation: Mol Cell Endocrinol. 2006 Jul 25;254-255:207-16
references.pmid: 16766117
references.citation: J Clin Endocrinol Metab. 2005 Dec;90(12):6396-402
references.pmid: 16189252
references.citation: Ann Rheum Dis. 1997 Jul;56(7):432-4
references.pmid: 9486006
references.citation: J Endocrinol Invest. 2010 Oct;33(9):644-9
references.pmid: 20339312
references.citation: Ann Anat. 2011 Feb 20;193(1):23-9
references.pmid: 20971625
references.citation: Ann Anat. 2001 May;183(3):223-7
references.pmid: 11396791
references.citation: J Orofac Pain. 2006 Spring;20(2):156-65
references.pmid: 16708833
references.citation: Arthritis Rheum. 2008 Jun;58(6):1696-700
references.pmid: 18512790
references.citation: J Bone Miner Res. 2005 Feb;20(2):232-9
references.pmid: 15647817
references.citation: J Cell Physiol. 2010 Mar;222(3):695-702
references.pmid: 20020445
references.citation: Bone. 2008 Sep;43(3):628-35
references.pmid: 18590994
references.citation: Prog Histochem Cytochem. 2011 Feb;45(4):239-93
references.pmid: 21251699
references.citation: Arthritis Res Ther. 2009;11(5):241
references.pmid: 19804619
references.citation: J Orthop Res. 2011 Oct;29(10):1563-71
references.pmid: 21469181
references.citation: Steroids. 1992 Oct;57(10):507-10
references.pmid: 1455459