Medin aggregation causes cerebrovascular dysfunction in aging wild-type mice.

Medin is the most common amyloid known in humans, as it can be found in blood vessels of the upper body in virtually everybody over 50 years of age. However, it remains unknown whether deposition of Medin plays a causal role in age-related vascular dysfunction. We now report that aggregates of Medin also develop in the aorta and brain vasculature of wild-type mice in an age-dependent manner. Strikingly, genetic deficiency of the Medin precursor protein, MFG-E8, eliminates not only vascular aggregates but also prevents age-associated decline of cerebrovascular function in mice. Given the prevalence of Medin aggregates in the general population and its role in vascular dysfunction with aging, targeting Medin may become a novel approach to sustain healthy aging.

Ovulation is triggered by a cyclical modulation of gonadotropes into a hyperexcitable state.

Gonadotropes in the anterior pituitary gland are essential for fertility and provide a functional link between the brain and the gonads. To trigger ovulation, gonadotrope cells release massive amounts of luteinizing hormone (LH). The mechanism underlying this remains unclear. Here, we utilize a mouse model expressing a genetically encoded Ca2+ indicator exclusively in gonadotropes to dissect this mechanism in intact pituitaries. We demonstrate that female gonadotropes exclusively exhibit a state of hyperexcitability during the LH surge, resulting in spontaneous [Ca2+]i transients in these cells, which persist in the absence of any in vivo hormonal signals. L-type Ca2+ channels and transient receptor potential channel A1 (TRPA1) together with intracellular reactive oxygen species (ROS) levels ensure this state of hyperexcitability. Consistent with this, virus-assisted triple knockout of Trpa1 and L-type Ca2+ subunits in gonadotropes leads to vaginal closure in cycling females. Our data provide insight into molecular mechanisms required for ovulation and reproductive success in mammals.

Hypothalamic neuroglial plasticity is regulated by anti-Müllerian hormone and disrupted in polycystic ovary syndrome.

BACKGROUND: Polycystic ovary syndrome (PCOS) is the most common reproductive-endocrine disorder affecting between 5 and 18% of women worldwide. An elevated frequency of pulsatile luteinizing hormone (LH) secretion and higher serum levels of anti-Müllerian hormone (AMH) are frequently observed in women with PCOS. The origin of these abnormalities is, however, not well understood. METHODS: We studied brain structure and function in women with and without PCOS using proton magnetic resonance spectroscopy (MRS) and diffusion tensor imaging combined with fiber tractography. Then, using a mouse model of PCOS, we investigated by electron microscopy whether AMH played a role on the regulation of hypothalamic structural plasticity. FINDINGS: Increased AMH serum levels are associated with increased hypothalamic activity/axonal-glial signalling in PCOS patients. Furthermore, we demonstrate that AMH promotes profound micro-structural changes in the murine hypothalamic median eminence (ME), creating a permissive environment for GnRH secretion. These include the retraction of the processes of specialized AMH-sensitive ependymo-glial cells called tanycytes, allowing more GnRH neuron terminals to approach ME blood capillaries both during the run-up to ovulation and in a mouse model of PCOS. INTERPRETATION: We uncovered a central function for AMH in the regulation of fertility by remodeling GnRH terminals and their tanycytic sheaths, and provided insights into the pivotal role of the brain in the establishment and maintenance of neuroendocrine dysfunction in PCOS. FUNDING: INSERM (U1172), European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement n° 725149), CHU de Lille, France (Bonus H).

Intra-pituitary follicle-stimulating hormone signaling regulates hepatic lipid metabolism in mice.

Inter-organ communication is a major hallmark of health and is often orchestrated by hormones released by the anterior pituitary gland. Pituitary gonadotropes secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH) to regulate gonadal function and control fertility. Whether FSH and LH also act on organs other than the gonads is debated. Here, we find that gonadotrope depletion in adult female mice triggers profound hypogonadism, obesity, glucose intolerance, fatty liver, and bone loss. The absence of sex steroids precipitates these phenotypes, with the notable exception of fatty liver, which results from ovary-independent actions of FSH. We uncover paracrine FSH action on pituitary corticotropes as a mechanism to restrain the production of corticosterone and prevent hepatic steatosis. Our data demonstrate that functional communication of two distinct hormone-secreting cell populations in the pituitary regulates hepatic lipid metabolism.

GnRH replacement rescues cognition in Down syndrome.

At the present time, no viable treatment exists for cognitive and olfactory deficits in Down syndrome (DS). We show in a DS model (Ts65Dn mice) that these progressive nonreproductive neurological symptoms closely parallel a postpubertal decrease in hypothalamic as well as extrahypothalamic expression of a master molecule that controls reproduction-gonadotropin-releasing hormone (GnRH)-and appear related to an imbalance in a microRNA-gene network known to regulate GnRH neuron maturation together with altered hippocampal synaptic transmission. Epigenetic, cellular, chemogenetic, and pharmacological interventions that restore physiological GnRH levels abolish olfactory and cognitive defects in Ts65Dn mice, whereas pulsatile GnRH therapy improves cognition and brain connectivity in adult DS patients. GnRH thus plays a crucial role in olfaction and cognition, and pulsatile GnRH therapy holds promise to improve cognitive deficits in DS.

Microglia Phenotypes Converge in Aging and Neurodegenerative Disease.

Microglia, the primary immune cells of the central nervous system, hold a multitude of tasks in order to ensure brain homeostasis and are one of the best predictors of biological age on a cellular level. We and others have shown that these long-lived cells undergo an aging process that impedes their ability to perform some of the most vital homeostatic functions such as immune surveillance, acute injury response, and clearance of debris. Microglia have been described as gradually transitioning from a homeostatic state to an activated state in response to various insults, as well as aging. However, microglia show diverse responses to presented stimuli in the form of acute injury or chronic disease. This complexity is potentially further compounded by the distinct alterations that globally occur in the aging process. In this review, we discuss factors that may contribute to microglial aging, as well as transcriptional microglia alterations that occur in old age. We then compare these distinct phenotypic changes with microglial phenotype in neurodegenerative disease.

Female sexual behavior in mice is controlled by kisspeptin neurons.

Sexual behavior is essential for the survival of many species. In female rodents, mate preference and copulatory behavior depend on pheromones and are synchronized with ovulation to ensure reproductive success. The neural circuits driving this orchestration in the brain have, however, remained elusive. Here, we demonstrate that neurons controlling ovulation in the mammalian brain are at the core of a branching neural circuit governing both mate preference and copulatory behavior. We show that male odors detected in the vomeronasal organ activate kisspeptin neurons in female mice. Classical kisspeptin/Kiss1R signaling subsequently triggers olfactory-driven mate preference. In contrast, copulatory behavior is elicited by kisspeptin neurons in a parallel circuit independent of Kiss1R involving nitric oxide signaling. Consistent with this, we find that kisspeptin neurons impinge onto nitric oxide-synthesizing neurons in the ventromedial hypothalamus. Our data establish kisspeptin neurons as a central regulatory hub orchestrating sexual behavior in the female mouse brain.

Genetic strategies to analyze primary TRP channel-expressing cells in mice.

Transient receptor potential (TRP) ion channels regulate fundamental biological processes throughout the body. TRP channel dysfunction has been causally linked to a number of disease states and thus establishes these channels as promising therapeutic targets. In order to dissect the physiological role of individual TRP channels in specific tissues, a detailed understanding of the expression pattern of the different TRP channels throughout the organism is essential. We provide an overview of recent efforts to generate novel TRP channel reporter mouse strains for all 28 TRP channels encoded in the mouse genome to understand expression of these channels with a single-cell resolution in an organism-wide manner. The reporter mice will enable both the visualization and manipulation of all primary TRP channel-expressing cells allowing an unprecedented wealth in variety to investigate TRP channel function in vivo. As proof of principle, we provide preliminary results documenting TRPM5 expression throughout the entire body of juvenile and adult mice.

Gene Targeting in Neuroendocrinology.

Research in neuroendocrinology faces particular challenges due to the complex interactions between cells in the hypothalamus, in the pituitary gland and in peripheral tissues. Within the hypothalamus alone, attempting to target a specific neuronal cell type can be problematic due to the heterogeneous nature and level of cellular diversity of hypothalamic nuclei. Because of the inherent complexity of the reproductive axis, the use of animal models and in vivo experiments are often a prerequisite in reproductive neuroendocrinology. The advent of targeted genetic modifications, particularly in mice, has opened new avenues of neuroendocrine research. Within this review, we evaluate various mouse models used in reproductive neuroendocrinology and discuss the different approaches to generate genetically modified mice, along with their inherent advantages and disadvantages. We also discuss a variety of versatile genetic tools with a focus on their potential use in reproductive neuroendocrinology.

Specialized subpopulations of kisspeptin neurons communicate with GnRH neurons in female mice.

The neuropeptide kisspeptin is a potent stimulator of GnRH neurons and has been implicated as a major regulator of the hypothalamus-pituitary-gonadal axis. There are mainly two anatomically segregated populations of neurons that express kisspeptin in the female hypothalamus: one in the anteroventral periventricular nucleus (AVPV) and the other in the arcuate nucleus (ARC). Distinct roles have been proposed for AVPV and ARC kisspeptin neurons during reproductive maturation and in mediating estrogen feedback on the hypothalamus-pituitary-gonadal axis in adults. Despite their pivotal role in the regulation of reproductive physiology, little is known about kisspeptin neuron connectivity. Although previous data suggest heterogeneity within the AVPV and ARC kisspeptin neuron populations, how many and which of these potential kisspeptin neuron subpopulations are actually communicating with GnRH neurons is not known. Here we used a combinatorial genetic transsynaptic tracing strategy to start to analyze the connectivity of individual kisspeptin neurons with the GnRH neuron population in female mice with a single-cell resolution. We find that only subsets of AVPV and ARC kisspeptin neurons are synaptically connected with GnRH neurons. We demonstrate that the majority of kisspeptin neurons within the AVPV and ARC does not communicate with GnRH neurons. Furthermore, we show that all kisspeptin neurons within the AVPV connected to GnRH neurons are estrogen sensitive and that most of these express tyrosine hydroxylase. Our data demonstrate functional specialization within the two kisspeptin neuron populations.