Sirt2‐BubR1 acetylation pathway mediates the effects of advanced maternal age on oocyte quality

Abstract

SummaryThe level of Sirt2 protein is reduced in oocytes from aged mice, while exogenous expression of Sirt2 could ameliorate the maternal age‐associated meiotic defects. To date, the underlying mechanism remains unclear. Here, we confirmed that specific depletion of Sirt2 disrupts maturational progression and spindle/chromosome organization in mouse oocytes, with compromised kinetochore–microtubule attachments. Candidate screening revealed that acetylation state of lysine 243 on BubR1 (BubR1‐K243, an integral part of the spindle assembly checkpoint complex) functions during oocyte meiosis, and acetylation‐mimetic mutant BubR1‐K243Q results in the very similar phenotypes as Sirt2‐knockdown oocytes. Furthermore, we found that nonacetylatable‐mimetic mutant BubR1‐K243R partly prevents the meiotic deficits in oocytes depleted of Sirt2. Importantly, BubR1‐K243R overexpression in oocytes derived from aged mice markedly suppresses spindle/chromosome anomalies and thereupon lowers the incidence of aneuploid eggs. In sum, our data suggest that Sirt2‐dependent BubR1 deacetylation involves in the regulation of meiotic apparatus in normal oocytes and mediates the effects of advanced maternal age on oocyte quality.

NAD+repletion rescues female fertility during reproductive ageing

“…Consequently, in oocytes from Sirt2 Tg/+ overexpressing animals, increases in kinetochore – microtubule stability likely contributed to augmented chromosome alignment and improved fertility. These observations are corroborated by separate in vitro studies where morpholino-mediated Sirt2 knockdown or chemical inhibition of SIRT2 in oocytes resulted in severe spindle defects and chromosome disorganization (29, 38). These results are supported by the apparent lower rates of aneuploidy in oocytes from aged Sirt2 Tg/+ animals in the present study.…”

“…4i), indicating that at a younger age where NAD is replete, SIRT2 is not essential for accurate spindle assembly, or that there is redundancy in the role of SIRT2 with other yet to be identified factors. These in vivo results from Sirt2 knockout animals are in contrast to studies of in vitro morpholino knockdown of Sirt2 (28) or chemical inhibition of SIRT2 in oocytes (38), where depletion or inhibition results in spindle assembly defects and aneuploidy (28, 29). The discrepancy between these results may be due to the compensatory, upregulation of other factors in constitutive knockout animals, versus the acute depletion of SIRT2 in oocytes during in vitro maturation.…”

“…The benefits of in vivo NMN treatment could largely be recapitulated by transgenic overexpression of Sirt2 in aged animals, although its constitutive deletion had no adverse impact on oocyte integrity, at least in the younger animals studied here. SIRT2 plays a role in the maintenance of microtubule-kinetochore attachments through its deacylation and stabilisation of BubR1 (26, 29), a process that ensures fidelity in chromosome separation through ensuring the bipolar orientation of chromosomes to the spindle. Consequently, in oocytes from Sirt2 Tg/+ overexpressing animals, increases in kinetochore – microtubule stability likely contributed to augmented chromosome alignment and improved fertility.…”

NAD+ Repletion Rescues Female Fertility during Reproductive Aging

“…Oocytes from whole-body Sirt2 À/À knockout mice at the age of 5-6 months displayed normal spindle assembly and maturation ( Figure 3I), indicating that at a younger age at which NAD + is replete, SIRT2 is not essential for accurate spindle assembly or that redundancy exists in the role of SIRT2 with other yet-to-be-identified factors. These in vivo results from Sirt2 knockout animals are in contrast to in vitro studies (Qiu et al, 2018;Riepsamen et al, 2015;Zhang et al, 2014). Altogether, (D and E) Aged (12-to 14-month-old) transgenic mice overexpressing NMNAT1 have increased oocyte yield (*p = 0.0416, two-tailed t-test, n = 8-10 per group) (D) in comparison to transgenics overexpressing NMNAT3 (n = 7-11) (E).…”

“…One candidate that we hypothesized for this role is the NAD + -dependent deacylase SIRT2. We previously showed that SIRT2 stabilizes the SAC protein BubR1 (North et al, 2014), which is critical for meiotic progression (Homer et al, 2009), kinetochore attachment, and chromosome segregation in oocytes (Qiu et al, 2018;Touati et al, 2015;Zhang et al, 2014). Levels of BubR1 decline in mouse reproductive tissue (North et al, 2014) and human oocytes with advancing age (Riris et al, 2014).…”