Neonatal uterine and vaginal cell proliferation and adenogenesis are independent of estrogen receptor 1 (ESR1) in the mouse.

Neonatal uterus and vagina express estrogen receptor 1 (ESR1) and respond mitogenically to exogenous estrogens. However, neonatal ovariectomy does not inhibit preweaning uterine cell proliferation, indicating that this process is estrogen independent. Extensive literature suggests that ESR1 can be activated by growth factors in a ligand-independent manner and drive uterine cell proliferation. Alternatively, neonatal uterine cell proliferation could be ESR1 independent despite its obligatory role in adult luminal epithelial proliferation. To determine ESR1's role in uterine and vaginal development, we analyzed cell proliferation, apoptosis, and uterine gland development (adenogenesis) in wild-type (WT) and Esr1 knockout (Esr1KO) mice from Postnatal Day 2 to Postnatal Day 60. Uterine and vaginal cell proliferation, apoptosis, and uterine adenogenesis were comparable in WT and Esr1KO mice before weaning. By Days 29-60, glands had regressed, and uterine cell proliferation was reduced in Esr1KO mice in contrast to continued adenogenesis and proliferation in WT. Apoptosis in Esr1KO uterine epithelium was not increased compared to WT at any age, indicating that differences in cell proliferation, rather than apoptosis, cause divergence of uterine size in these two groups at puberty. Similarly, vaginal epithelial proliferation was reduced, and the epithelium became atrophic in Esr1KO mice by 29 days of age and later in Esr1KO mice. These results indicate that preweaning uterine and vaginal development is ESR1 independent but becomes dependent on ESR1 by Day 29 on. It is not yet clear what mechanisms drive preweaning vaginal and uterine development, but ligand-independent activation of ESR1 is not involved.

Differences in memory development among C57BL/6NCrl, 129S2/SvPasCrl, and FVB/NCrl mice after delay and trace fear conditioning.

Fear-conditioning testing paradigms have been used to study differences in memory formation between inbred mouse strains, including numerous mouse models of human diseases. In this study, we characterized the conditioned fear memory of 3 inbred strains: C57BL/6NCrl, 129S2/SvPasCrl, and FVB/NCrl, obtained from Charles River Laboratories. We used 2 training paradigms: delay conditioning, in which an unconditional stimulus coterminates with the presentation of a conditional stimulus, and trace conditioning, in which the conditional and unconditional stimuli are separated by a trace interval. In each paradigm, we evaluated the recent (3 d) and remote (25 d) memory of the mice by using a longitudinal design. Our results showed that both C57BL/6NCrl and 129S2/SvPasCrl mice developed strong and long-lasting context and tone memories in both paradigms, but FVB/NCrl mice showed a weaker but nevertheless consistent tone memory after delay training. Tone memory in the FVB strain was stronger in male than female mice. The remote tone memory of 129S2/SvPasCrl mice diminished after delay training but was stable and stronger than that of C57BL/6NCrl mice after trace training. In conclusion, both C57BL/6NCrl and 129S2/SvPasCrl mice showed reliable and long-lasting fear memory after delay or trace training, with 129 mice showing particularly strong tone memory after trace conditioning. The FVB/NCrl strain, especially male mice, showed reliable tone fear memory after delay training. Our findings confirm that both C57BL/6NCrl and 129S2/SvPasCrl mice develop strong context and tone memory in delay and trace fear-conditioning paradigms.

Normal cognition in transgenic BRI2-Aß mice.

BACKGROUND: Recent research in Alzheimer's disease (AD) field has been focused on the potential role of the amyloid-ß protein that is derived from the transmembrane amyloid precursor protein (APP) in directly mediating cognitive impairment in AD. Transgenic mouse models overexpressing APP develop robust AD-like amyloid pathology in the brain and show various levels of cognitive decline. In the present study, we examined the cognition of the BRI2-Aß transgenic mouse model in which secreted extracellular Aß1-40, Aß1-42 or both Aß1-40/Aß1-42 peptides are generated from the BRI-Aß fusion proteins encoded by the transgenes. BRI2-Aß mice produce high levels of Aß peptides and BRI2-Aß1-42 mice develop amyloid pathology that is similar to the pathology observed in mutant human APP transgenic models. RESULTS: Using established behavioral tests that reveal deficits in APP transgenic models, BRI2-Aß1-42 mice showed completely intact cognitive performance at ages both pre and post amyloid plaque formation. BRI2-Aß mice producing Aß1-40 or both peptides were also cognitively intact. CONCLUSIONS: These data indicate that high levels of Aß1-40 or Aß1-42, or both produced in the absence of APP overexpression do not reproduce memory deficits observed in APP transgenic mouse models. This outcome is supportive of recent data suggesting that APP processing derivatives or the overexpression of full length APP may contribute to cognitive decline in APP transgenic mouse models. Alternatively, Aß aggregates may impact cognition by a mechanism that is not fully recapitulated in these BRI2-Aß mouse models.

Reduction of beta-amyloid pathology by celastrol in a transgenic mouse model of Alzheimer's disease.

BACKGROUND: Abeta deposits represent a neuropathological hallmark of Alzheimer's disease (AD). Both soluble and insoluble Abeta species are considered to be responsible for initiating the pathological cascade that eventually leads to AD. Therefore, the identification of therapeutic approaches that can lower Abeta production or accumulation remains a priority. NFkappaB has been shown to regulate BACE-1 expression level, the rate limiting enzyme responsible for the production of Abeta. We therefore explored whether the known NFkappaB inhibitor celastrol could represent a suitable compound for decreasing Abeta production and accumulation in vivo. METHODS: The effect of celastrol on amyloid precursor protein (APP) processing, Abeta production and NFkappaB activation was investigated by western blotting and ELISAs using a cell line overexpressing APP. The impact of celastrol on brain Abeta accumulation was tested in a transgenic mouse model of AD overexpressing the human APP695sw mutation and the presenilin-1 mutation M146L (Tg PS1/APPsw) by immunostaining and ELISAs. An acute treatment with celastrol was investigated by administering celastrol intraperitoneally at a dosage of 1 mg/Kg in 35 week-old Tg PS1/APPsw for 4 consecutive days. In addition, a chronic treatment (32 days) with celastrol was tested using a matrix-driven delivery pellet system implanted subcutaneously in 5 month-old Tg PS1/APPsw to ensure a continuous daily release of 2.5 mg/Kg of celastrol. RESULTS: In vitro, celastrol dose dependently prevented NFkappaB activation and inhibited BACE-1 expression. Celastrol potently inhibited Abeta1-40 and Abeta1-42 production by reducing the beta-cleavage of APP, leading to decreased levels of APP-CTFbeta and APPsbeta. In vivo, celastrol appeared to reduce the levels of both soluble and insoluble Abeta1-38, Abeta1-40 and Abeta1-42. In addition, a reduction in Abeta plaque burden and microglial activation was observed in the brains of Tg PS1/APPsw following a chronic administration of celastrol. CONCLUSIONS: Overall our data suggest that celastrol is a potent Abeta lowering compound that acts as an indirect BACE-1 inhibitor possibly by regulating BACE-1 expression level via an NFkappaB dependent mechanism. Additional work is required to determine whether chronic administration of celastrol can be safely achieved with cognitive benefits in a transgenic mouse model of AD.