Chronic Stimulation of Arcuate Kiss1 Neurons Decreases Bone Mass in Female Mice

Loss of peripheral estrogen in postmenopausal women is often associated with decreased physical activity and loss of bone mass, leading to an increased risk of metabolic diseases, osteoporosis, and skeletal fragility. While it is well-established that loss of peripheral estrogen signaling results in bone loss, we previously found that eliminating central estrogen signaling paradoxically results in an unexpected massive increase in bone mass only in female mice. Specifically, deletion of estrogen receptor alpha (ERα) signaling in kisspeptin 1 (Kiss1) expressing neurons of the arcuate nucleus (ARC(Kiss1)) increases bone mass at the expense of reproduction in female mice. Currently, the mechanisms and the neurocircuits that modulate these unexpected responses are unknown. Here, to begin addressing these questions, we asked if changing the neuronal output of ARC(Kiss1) neurons using chemogenetic manipulation of ARC(Kiss1) neurons might also alter bone mass and locomotion in female mice. To do this, we delivered stimulatory (AAV2-hM3Dq-mCherry) designer receptors exclusively activated by designer drugs (DREADDs) to the ARC of wild type and Kiss1-Cre+ (Kiss1-Cre(hM3q-DREADDs)) female mice and asked if chronic activation of ARC(Kiss1) neurons might alter bone mass as analyzed by standard ex-vivo µCT imaging. Clozapine N-oxide (CNO) was delivered for 22 days (0.1 mg/mL). We also leveraged the ANY-Maze system to assess home cage activity over an extensive 96-hour period. Acute activation of ARC(Kiss1) tended to decrease home cage activity by nearly 40% in Kiss1-Cre(hM3q-DREADDs) mice during the dark period compared to WT females. Interestingly, chronic activation of ARC(Kiss1) neurons significantly lowered trabecular bone volume by nearly 30%. Current studies are underway to ask if inhibiting ARC(Kiss1) neurons results in increased bone mass. Our findings collectively suggest that the neuronal activity of ARC(Kiss1) neurons is sufficient to shift energy allocation away from locomotion and bone-building to maximize reproductive capacity. We speculate that the widely used SERM in breast cancer treatment, Tamoxifen, might exert its bone sparing effect by silencing ARC(Kiss1) neurons.