Matrix metalloproteinase inhibition influences aspects of photoperiod stimulated ovarian recrudescence in Siberian hamsters

Transcriptome analysis during photostimulated recrudescence reveals distinct patterns of gene regulation in Siberian hamster ovaries†

In Siberian hamsters, exposure to short days (SDs, 8 h light:16 h dark) reduces reproductive function centrally by decreasing gonadotropin secretion, whereas subsequent transfer of photoinhibited hamsters to stimulatory long days (LDs, 16 L:8 D) promotes follicle stimulating hormone (FSH) release inducing ovarian recrudescence. Although differences between SD and LD ovaries have been investigated, a systematic investigation of the ovarian transcriptome across photoperiod groups to identify potentially novel factors that contribute to photostimulated restoration of ovarian function had not been conducted. Hamsters were assigned to one of four photoperiod groups: LD to maintain ovarian cyclicity, SD to induce ovarian regression, or post transfer (PT), where females housed in SD for 14-weeks were transferred to LD for 2-days or 1-week to reflect photostimulated ovaries prior to (PTd2) and following (PTw1) the return of systemic FSH. Ovarian RNA was extracted to create RNA-sequencing libraries and short-read sequencing Illumina assays that mapped and quantified the ovarian transcriptomes (n = 4/group). Ovarian and uterine masses, plasma FSH, and numbers of antral follicles and corpora lutea decreased in SD as compared to LD ovaries (P < 0.05). When reads were aligned to the mouse genome, 18 548 genes were sufficiently quantified. Most of the differentially expressed genes noted between functional LD ovaries and regressed SD ovaries; however, five main expression patterns were identified across photoperiod groups. These results, generally corroborated by select protein immunostaining, provide a map of photoregulated ovary function and identify novel genes that may contribute to the photostimulated resumption of ovarian activity.

Lipotoxicity, neuroinflammation, glial cells and oestrogenic compounds

The high concentrations of free fatty acids as a consequence of obesity and being overweight have become risk factors for the development of different diseases, including neurodegenerative ailments. Free fatty acids are strongly related to inflammatory events, causing cellular and tissue alterations in the brain, including cell death, deficits in neurogenesis and gliogenesis, and cognitive decline. It has been reported that people with a high body mass index have a higher risk of suffering from Alzheimer's disease. Hormones such as oestradiol not only have beneficial effects on brain tissue, but also exert some adverse effects on peripheral tissues, including the ovary and breast. For this reason, some studies have evaluated the protective effect of oestrogen receptor (ER) agonists with more specific tissue activities, such as the neuroactive steroid tibolone. Activation of ERs positively affects the expression of pro-survival factors and cell signalling pathways, thus promoting cell survival. This review aims to discuss the relationship between lipotoxicity and the development of neurodegenerative diseases. We also elaborate on the cellular and molecular mechanisms involved in neuroprotection induced by oestrogens.

Assessing recrudescence of photoregressed Siberian hamster ovaries using in vitro whole ovary culture

In vitro culture has been used to study different aspects of ovarian function; however, this technique has not been applied to study recrudescence, or the return of ovarian function in seasonally breeding species. In Siberian hamsters, exposure to inhibitory photoperiods induces declines in ovarian function, which are restored with photostimulation. Because these changes are mediated by changes in systemic gonadotropin (GT) secretion, we hypothesized that culturing photoregressed ovaries with GT would restore aspects of function and induce expression of key folliculogenic factors. Adult female Siberian hamsters were exposed to either long-day (LD; 16L:8D) or short-day (SD; 8L:16D) photoperiods for 14 weeks to maintain in vivo cyclicity or induce gonadal regression, respectively. Isolated ovaries were then cultured for 10 days with or without GT. Ovarian mass and messenger RNA (mRNA) expression of mitotic marker Pcna were increased in cultured SD ovaries (cSD) ovaries with GT as compared to without GT, with no changes noted among cultured LD (cLD) ovaries. Media estradiol and progesterone concentrations increased in both cLD and cSD ovaries cultured with GT as compared to without GT. No differences in follicle numbers or incidence of apoptosis were noted across groups. In addition, differential mRNA expression of folliculogenic growth factors ( Bmp-4, Ntf-3, Inh-α, Gdf-9, Igf-1, Has-2, and Cox-2) was observed in cSD treated with or without GT. Together, these results suggest that this in vitro model could be a useful tool to (a) study the return of function in photoregressed ovaries, and (b) to identify the specific roles folliculogenic factors play in ovarian recrudescence.

Folliculogenic factors in photoregressed ovaries: Differences in mRNA expression in early compared to late follicle development

The early stages of ovarian folliculogenesis generally progress independent of gonadotropins, whereas later stages require signaling initiated by FSH. In Siberian hamsters, cycles of folliculogenesis are mediated by changes in photoperiod which depress the hypothalamic pituitary gonadal axis. Reduced gonadotropins lead to decreases in mature follicle development and ovulation; however, early stages of folliculogenesis have not been explored in regressed ovaries. We hypothesized that intraovarian factors that contribute predominantly to later stages of folliculogenesis would react to changes in photoperiod, whereas factors contributing to earlier stages would not change. To probe if the early stages of folliculogenesis continue in the photoinhibited ovary while late stages decline, we measured the mRNA abundance of factors that interact with FSH signaling (Fshr, Igf1, Cox2) and factors that can function independently of FSH (c-Kit, Kitl, Foxo3, Figla, Nobox, Sohlh1, Lhx8). While plasma FSH, antral follicles, and corpora lutea numbers declined with exposure to inhibitory photoperiod, the numbers of primordial, primary, and secondary follicles did not change. Expression of factors that interact with FSH signaling changed with changes in photoperiod; however, expression of factors that do not interact with FSH were not significantly altered. These results suggest that the photoinhibited ovary is not completely quiescent, as factors important for follicle selection and early follicle growth are still expressed in regressed ovaries. Instead, the lack of gonadotropin support that characterizes the non-breeding season appears to inhibit only final stages of folliculogenesis in Siberian hamsters.

Photoperiodic Regulation of Cerebral Blood Flow in White-Footed Mice (Peromyscus leucopus)

Individuals living outside the tropics need to adjust their behavioral and physiological repertoires throughout the year to adapt to the changing seasons. White-footed mice (Peromyscus leucopus) reduce hippocampal volumes, hippocampal-dependent memory function, long-term potentiation, and alter neurogenesis in response to short (winter-like) day lengths (photoperiods). During winter, these mice putatively shunt energy away from the brain to maximize peripheral thermogenesis, immune function, and survival. We hypothesized that these changes in brain function are accompanied by alterations in brain vasculature. We maintained white-footed mice in short (8 h light/16 h dark) or long (16 h light/8 h dark) photoperiods for 8–9 weeks. Mice were then perfused with fluorescein isothiocyanate (FITC)-conjugated tomato (Lycopersicon esculentum) lectin to visualize the perfused cerebrovasculature. Short-day mice reduced hippocampal and cortical capillary density (FITC⁺ area); vessels isolated from short day-exposed mice expressed higher mRNA levels of the gelatinase matrix metalloproteinase 2 (MMP2). Additionally, short-day mice reduced cerebral blood flow ∼15% compared with their long-day counterparts, as assessed by laser speckle flowmetry. Immunohistochemistry revealed higher levels of MMP2 in the hippocampus of mice maintained in short days compared with long days, potentially contributing to the observed vascular remodeling. These data demonstrate that a discrete environmental signal (i.e., day length) can substantially alter cerebral blood flow in adult mammals.