8060 SIRT4 Plays a Role in Mammary Gland Development

Abstract Disclosure: B. deSouza: None. F. Huynh: None. K. Anderson: None. I. Batchvarov: None. B. Capel: None. M. Hirschey: None. Breastfeeding confers a wealth of benefits to both children and mothers. Breastfeeding can be impaired by metabolic diseases such as diabetes and obesity, which are known to interfere with both normal mammary gland development and lactogenesis, although mechanisms remain unclear. Our lab recently discovered a novel connection between metabolic regulation and mammary development in Sirt4 knockout (Sirt4-/-) mice. SIRT4 is an NAD+-dependent mitochondrial enzyme with strong deacylase activity. It is known to regulate several metabolic pathways including those of fatty acids, glutamine, and leucine. Sirt4 knockout mice are resistant to developing high-fat diet-induced obesity but develop early-onset insulin resistance. We observed that Sirt4-/- females are incapable of nursing their offspring due to impaired mammary ductal branching. Transplantation of wild-type mammary epithelia into SIRT4KO mice fails to rescue mammary development; however, mammary epithelia from SIRTKO mice transplanted into wild-type mice develop normally. SIRT4 action is thus required outside the mammary gland, which led us to explore the effect of SIRT4 on steroid hormone signaling. Treatment of pre-pubertal SIRT4KO mice with progesterone and estradiol, but not estradiol alone, rescued mammary ductal branching. Likewise, transplants of wild-type ovaries into SIRT4KO mice partially rescued the ductal branching defect. Given these findings, we hypothesized that SIRT4 expression in the ovary is necessary for sufficient progesterone biosynthesis and subsequent mammary development. In ovaries of adult mice, SIRT4 is most highly expressed in differentiated granulosa cells of the corpus luteum, a temporary endocrine structure responsible for synthesizing peak levels of progesterone during the diestrus phase of the mouse estrous cycle. Future experiments will compare peak circulating progesterone levels in Sirt4-/- vs. wild-type mice. We will characterize progesterone signaling in SIRT4KO mammary glands, including determining the expression of progesterone receptor isoforms. Additionally, we will characterize SIRT4 function in the ovary, including its effects on corpus luteum formation, steroid hormone biosynthesis, and import vs. de novo synthesis of the steroidogenic precursor, cholesterol. This work could offer new insights into the impairment of breastfeeding due to metabolic diseases. Presentation: 6/3/2024