Michelle Van Sinderen

Publications (3)8.89 Total impact

• Article: Estrogen deficiency reversibly induces telomere shortening in mouse granulosa cells and ovarian aging in vivo.

  Sharyn Bayne, He Li, Margaret E E Jones, Alex R Pinto, Michelle van Sinderen, Ann Drummond, Evan R Simpson, Jun-Ping Liu
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  ABSTRACT: Estrogen is implicated as playing an important role in aging and tumorigenesis of estrogen responsive tissues; however the mechanisms underlying the mitogenic actions of estrogen are not fully understood. Here we report that estrogen deficiency in mice caused by targeted disruption of the aromatase gene results in a significant inhibition of telomerase maintenance of telomeres in mouse ovaries in a tissue-specific manner. The inhibition entails a significant shortening of telomeres and compromised proliferation in the follicular granulosa cell compartment of ovary. Gene expression analysis showed decreased levels of proto-oncogene c-Myc and the telomerase catalytic subunit, telomerase reverse transcriptase (TERT), in response to estrogen deficiency. Estrogen replacement therapy led to increases in TERT gene expression, telomerase activity, telomere length and ovarian tissue growth, thereby reinstating ovary development to normal in four weeks. Our data demonstrate for the first time that telomere maintenance is the primary mechanism mediating the mitogenic effect of estrogen on ovarian granulosa cell proliferation by upregulating the genes of c-Myc and TERT in vivo. Estrogen deficiency or over-activity may cause ovarian tissue aging or tumorigenesis, respectively, through estrogen regulation of telomere remodeling.
  Protein & Cell 04/2011; 2(4):333-46.
• Source

  Available from: Maarten van den Buuse

  Article: Differential effect of amphetamine on c-fos expression in female aromatase knockout (ArKO) mice compared to wildtype controls.

  Carolina Chavez, Andrea Gogos, Rachel Hill, Michelle Van Sinderen, Evan Simpson, Wah Chin Boon, Maarten van den Buuse
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  ABSTRACT: Estrogen may be involved in psychosis by an interaction with central dopaminergic activity. Aromatase knockout mice are unable to produce estrogen and have been shown to display altered behavioural responses and effects of the dopamine releaser, amphetamine. This study investigates the effect of gonadal status on amphetamine-induced c-fos expression in the brains of female aromatase knockout and wildtype mice. Six groups of mice were treated intraperitoneally with saline or 5mg/kg amphetamine. Fos immunoreactivity was assessed in the cingulate cortex, caudate putamen and nucleus accumbens. Aromatase knockout mice showed markedly reduced amphetamine-induced Fos immunoreactivity compared to wildtype mice. However, the amphetamine response was restored in aromatase-knockout mice after ovariectomy, which reduced this effect in wildtype controls. Estrogen supplementation reversed the effect of ovariectomy in wildtype mice but had no additional significant effect in aromatase-knockout mice. These results indicate that mechanisms involved in amphetamine-induced c-fos expression are altered in aromatase knockout mice and that the primary hormone involved in this effect is not estrogen, but may be another factor released from the ovaries, such as an androgen. These results provide new insight into the effect of gonadal hormones on amphetamine induced c-fos expression in this mouse model of estrogen deficiency. These results could be important for our understanding of the role of sex steroid hormones in psychosis.
  Psychoneuroendocrinology 11/2010; 36(5):761-8. · 5.81 Impact Factor
• Article: The estrogenic component of tibolone reduces adiposity in female aromatase knockout mice.

  Michelle L Van Sinderen, Wah Chin Boon, Antwan G H Ederveen, Helenius J Kloosterboer, Evan R Simpson, Margaret E E Jones
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  ABSTRACT: To explore the effects of tibolone on adiposity in the absence of aromatase and determine which of the hormonal properties of tibolone are exerting these effects. In this study, vehicle; tibolone; estrogenic (ethinyl estradiol [EE]), progestogenic (ORG2058), or androgenic (dihydrotestosterone) compounds; or a combination of ORG2058 + EE was administered to 6-month-old ovariectomized aromatase knockout (ArKO) mice for a period of 6 weeks. In response to tibolone or EE-alone treatments, omental adipose tissue and infrarenal adipose tissue weights were significantly reduced (P = 0.004 and P = 0.01; P = 0.009 and P = 0.014, respectively) compared with those in ovariectomized and vehicle-treated ArKO mice. In contrast, adipose tissue weight tended to increase after ORG2058-alone treatment. Furthermore, EE in the presence of ORG2058 (ORG2058 + EE group) results in little effect on adiposity when compared with that in ovariectomized and vehicle-treated ArKO mice, showing that ORG2058 can negate the effect of EE. Dihydrotestosterone treatment did not have an impact on adipose tissue mass. Adipocyte volume and numbers followed the same treatment trends. In summary, our study in the ArKO mouse has confirmed the efficacy of tibolone as a hormone therapy to reduce adipose tissue accumulation after menopause and also shows that aromatization of tibolone is not required to elicit these estrogenic effects.
  Menopause (New York, N.Y.) 02/2009; 16(3):582-8. · 3.08 Impact Factor