Dicer ablation in Kiss1 neurons impairs puberty and fertility preferentially in female mice

Central lipid sensing pathways contribute to the control of puberty and its alterations in conditions of obesity

Childhood obesity, especially in girls, often correlates with advanced puberty and long-term comorbidities. Among the central circuits controlling energy homeostasis, hypothalamic lipid sensing pathways, involving free fatty-acid receptors (FFARs), peroxisome proliferator-activated receptors (PPARs), and the bile-acid (BA) receptor, Takeda G protein-coupled receptor 5 (TGR5), have been recognized as major players, with putative pathogenic roles in obesity and its complications. However, their contribution to pubertal regulation and obesity-induced pubertal alterations remains largely unexplored. We describe herein changes in the hypothalamic profiles of specific lipid species, including certain fatty-acyls, BA derivatives, and several glycerolphospholipids, during the juvenile-pubertal transition and conditions of overweight linked to precocious puberty in female rats. Hypothalamic expression of the FFAR, Gpr84, as well as Ppar-γ and Tgr5 gradually increased during the infantile-prepubertal transition, whereas early overfeeding increased hypothalamic mRNA levels of the FFARs, Gpr43, and Gpr84. Expression of Gpr84, Ppar-α, and Tgr5 was documented in FACS-isolated Kiss1 neurons from juvenile and pubertal female mice. Central pharmacological gain- and loss-of-function manipulations of GPR84-, PPAR-, or TGR5-signaling in prepubertal lean and early overfed female rats resulted in specific changes in pubertal timing. In lean rats, central blockade of PPAR-γ/α delayed puberty onset, whereas in early overfed rats, central stimulation of TGR5 signaling partially prevented obesity-induced advanced puberty; effects that were also marginally observed after GPR84 inhibition. Our results disclose the role of brain lipid-sensing pathways in the control of puberty, with a variable contribution of central FFAR-, PPAR-, and TGR5-signaling depending on the maturational and nutritional status.NEW & NOTEWORTHY Puberty is highly sensitive to body energy status, and child obesity is often linked to perturbed puberty. However, whether this comes from excessive energy stores or specific nutrient signals altered in obesity remains largely unexplored. Using suitable preclinical models of early obesity and accelerated puberty, we disclose herein conclusive evidence for altered hypothalamic lipid profiles and the roles of specific lipid-sensing pathways in pubertal control, with a variable contribution depending on the maturational and nutritional status.

Intranasal kisspeptin administration rapidly stimulates gonadotropin release in humans

BACKGROUND

Kisspeptin administration by intravenous or subcutaneous routes activates hypothalamic gonadotropin-releasing hormone (GnRH) neurons and is being developed to treat reproductive disorders. However, these invasive routes markedly limit patient acceptability and clinical use. Recent rodent data has identified a large GnRH population within the olfactory system communicating directly with hypothalamic GnRH neurons. Intranasal kisspeptin administration may be able to capitalise on this novel pathway and thus offer a potential non-invasive approach to stimulate reproductive hormones. Herein, we examine intranasal kisspeptin using human, pharmaceutical, and rodent studies.

METHODS

Reproductive hormone profiles were measured after intranasal kisspeptin administration in healthy volunteers and patients with reproductive disorders as part of a randomised, double-blinded, crossover, placebo-controlled clinical study. Pharmaceutical testing evaluated the chemical stability and nasal kisspeptin delivery, and rodent studies provided mechanistic insight.

FINDINGS

Intranasal kisspeptin-54 rapidly stimulates gonadotropin release in healthy men and women, and in patients with a common reproductive disorder (hypothalamic amenorrhoea), without any side effects or adverse events encountered. Specifically, intranasal kisspeptin (at 12.8 nmol/kg) induced clinically-significant mean maximal increases above baseline in serum luteinising hormone in all study groups: 4.4 ± 0.6 IU/L (mean difference = 3.1 IU/L [95% CI, 1.2-4.9], P = 0.002 vs. placebo) in healthy men; 1.4 ± 0.3 IU/L (mean difference = 1.0 IU/L [95% CI, 0.4-1.7], P = 0.004 vs. placebo) in healthy women; 4.4 ± 0.2 IU/L (mean difference = 4.3 IU/L [95% CI, 2.7-6.0], P < 0.001 vs. placebo) in patients with hypothalamic amenorrhoea. Kisspeptin-54 was delivered effectively via nasal spray and was stable for up to 60 days at 4 °C. Mirroring the human effects, intranasal kisspeptin-54 in adult C57BL/6J male mice stimulates luteinising hormone release. Further mechanistic insights reveal the accumulation of fluorescently-tagged kisspeptin in the olfactory epithelium, as well as the presence of kisspeptin receptors in olfactory bulb GnRH neurons, implicating the involvement of these extra-hypothalamic GnRH neurons in the pathway mediating intranasal kisspeptin's effects on reproductive hormones.

INTERPRETATION

We demonstrate the clinical potential for intranasal kisspeptin delivery as the first non-invasive method to robustly and safely stimulate gonadotropins with kisspeptin and potentially transform the management of reproductive disorders.

FUNDING

National Institute for Health and Care Research (NIHR)/NIHR Imperial Biomedical Research Centre/Medical Research Council (MRC).

Kisspeptin and neurokinin B: roles in reproductive health

Kisspeptin and neurokinin B (NKB) play a key role in several physiological processes including in puberty, adult reproductive function including the menstrual cycle, as well as mediating the symptoms of menopause. Infundibular kisspeptin neurons, which coexpress NKB, regulate the activity of gonadotropin-releasing hormone (GnRH) neurons and thus the physiological pulsatile secretion of GnRH from the hypothalamus. Outside of their hypothalamic reproductive roles, these peptides are implicated in several physiological functions including sexual behavior and attraction, placental function, and bone health. Over the last two decades, research findings have considerably enhanced our understanding of the physiological regulation of the hypothalamic-pituitary-gonadal (HPG) axis and identified potential therapeutic applications. For example, recognition of the role of kisspeptin as the natural inductor of ovulation has led to research investigating its use as a safer, more physiological trigger of oocyte maturation in in vitro fertilization (IVF) treatment. Moreover, the key role of NKB in the pathophysiology of menopausal hot flashes has led to the development of pharmacological antagonism of this pathway. Indeed, fezolinetant, a neurokinin 3 receptor antagonist, has recently received Food and Drug Administration (FDA) approval for clinical use to treat menopausal vasomotor symptoms. Here, we discuss the roles of kisspeptin and NKB in human physiology, including in the regulation of puberty, menstrual cyclicity, reproductive behavior, pregnancy, menopause, and bone homeostasis. We describe how perturbations of these key physiological processes can result in disease states and consider how kisspeptin and NKB could be exploited diagnostically as well as therapeutically to treat reproductive disorders.

GnRH and Cognition

GnRH is traditionally recognized as the central regulator of reproduction through its pulsatile secretion, which governs the hypothalamic-pituitary-gonadal axis. However, recent evidence has highlighted its broader role in brain development and function, including in cognitive and higher intellectual processes. GnRH production follows distinct phases, from its early activation during minipuberty-the first postnatal activation of GnRH neurons during the infantile period-, its reactivation and stabilization starting at puberty, and its eventual decline with age and the loss of gonadal steroid feedback. This evolution depends on the establishment, maturation and activation of GnRH neurons, a complex process regulated by the cellular and molecular environment of these neurons, including multiple neuronal and glial types as well as a minipubertal "switch" in gene expression, the perturbation of which may have long-term or delayed consequences for both reproductive and cognitive function. The cognitive role of GnRH may be related to its recently revealed involvement in maintaining myelination and synaptic plasticity, whereas disruptions in its finely tuned rhythmic secretion, either age-related or pathological, are associated with cognitive decline and neurodegenerative disorders. Restoring physiological GnRH levels and pulsatility can reverse age-related cognitive decline and improve sensory functions even in adulthood, suggesting a mobilization of the "cognitive reserve" in both animal models and human patients. This review highlights recent advances in our understanding of the GnRH system and the therapeutic potential of pulsatile GnRH therapy to mitigate age-related cognitive decline and neurodegenerative processes.

Diversity of Molecular Functions of RNA-Binding Ubiquitin Ligases from the MKRN Protein Family

Makorin RING finger protein family includes four members (MKRN1, MKRN2, MKRN3, and MKRN4) that belong to E3 ubiquitin ligases and play a key role in various biological processes, such as cell survival, cell differentiation, and innate and adaptive immunity. MKRN1 contributes to the tumor growth suppression, energy metabolism, anti-pathogen defense, and apoptosis and has a broad variety of targets, including hTERT, APC, FADD, p21, and various viral proteins. MKRN2 regulates cell proliferation, inflammatory response; its targets are p65, PKM2, STAT1, and other proteins. MKRN3 is a master regulator of puberty timing; it controls the levels of gonadotropin-releasing hormone in the arcuate nucleus neurons. MKRN4 is the least studied member of the MKRN protein family, however, it is known to contribute to the T cell activation by ubiquitination of serine/threonine kinase MAP4K3. Proteins of the MKRN family are associated with the development of numerous diseases, for example, systemic lupus erythematosus, central precocious puberty, Prader-Willi syndrome, degenerative lumbar spinal stenosis, inflammation, and cancer. In this review, we discuss the functional roles of all members of the MKRN protein family and their involvement in the development of diseases.

The evolutionary conserved miR-137/325 tandem mediates obesity-induced hypogonadism and metabolic comorbidities by repressing hypothalamic kisspeptin

BACKGROUND

Obesity-induced hypogonadism (OIH) is a prevalent, but often neglected condition in men, which aggravates the metabolic complications of overweight. While hypothalamic suppression of Kiss1-encoded kisspeptin has been suggested to contribute to OIH, the molecular mechanisms for such repression in obesity, and the therapeutic implications thereof, remain unknown.

METHODS

A combination of bioinformatic, expression and functional analyses was implemented, assessing the role of the evolutionary-conserved miRNAs, miR-137 and miR-325, in mediating obesity-induced suppression of hypothalamic kisspeptin, as putative mechanism of central hypogonadism and metabolic comorbidities. The implications of such miR-137/325-kisspeptin interplay for therapeutic intervention in obesity were also explored using preclinical OIH models.

RESULTS

MiR-137/325 repressed human KISS1 3'-UTR in-vitro and inhibited hypothalamic kisspeptin content in male rats, while miR-137/325 expression was up-regulated, and Kiss1/kisspeptin decreased, in the medio-basal hypothalamus of obese rats. Selective over-expression of miR-137 in Kiss1 neurons reduced Kiss1/ kisspeptin and partially replicated reproductive and metabolic alterations of OIH in lean mice. Conversely, interference of the repressive actions of miR-137/325 selectively on Kiss1 3'-UTR in vivo, using target-site blockers (TSB), enhanced kisspeptin content and reversed central hypogonadism in obese rats, together with improvement of glucose intolerance, insulin resistance and cardiovascular and inflammatory markers, despite persistent exposure to obesogenic diet. Reversal of OIH by TSB miR-137/325 was more effective than chronic kisspeptin or testosterone treatments in obese rats.

CONCLUSIONS

Our data disclose that the miR-137/325-Kisspeptin repressive interaction is a major player in the pathogenesis of obesity-induced hypogonadism and a putative druggable target for improved management of this condition and its metabolic comorbidities in men suffering obesity.

SIGNIFICANCE STATEMENT

Up to half of the men suffering obesity display also central hypogonadism, an often neglected complication of overweight that can aggravate the clinical course of obesity and its complications. The mechanisms for such obesity-induced hypogonadism remain poorly defined. We show here that the evolutionary conserved miR137/miR325 tandem centrally mediates obesity-induced hypogonadism via repression of the reproductive-stimulatory signal, kisspeptin; this may represent an amenable druggable target for improved management of hypogonadism and other metabolic complications of obesity.

Micromanaging the neuroendocrine system - A review on miR-7 and the other physiologically relevant miRNAs in the hypothalamic-pituitary axis

The hypothalamic-pituitary axis is central to the functioning of the neuroendocrine system and essential for regulating physiological and behavioral homeostasis and coordinating fundamental body functions. The expanding line of evidence shows the indispensable role of the microRNA pathway in regulating the gene expression profile in the developing and adult hypothalamus and pituitary gland. Experiments provoking a depletion of miRNA maturation in the context of the hypothalamic-pituitary axis brought into focus a prominent involvement of miRNAs in neuroendocrine functions. There are also a few individual miRNAs and miRNA families that have been studied in depth revealing their crucial role in mediating the regulation of fundamental processes such as temporal precision of puberty timing, hormone production, fertility and reproduction capacity, and energy balance. Among these miRNAs, miR-7 was shown to be hypothalamus-enriched and the top one highly expressed in the pituitary gland, where it has a profound impact on gene expression regulation. Here, we review miRNA profiles, knockout phenotypes, and miRNA interaction (targets) in the hypothalamic-pituitary axis that advance our understanding of the roles of miRNAs in mammalian neurosecretion and related physiology.

Endocrine Disruptors and Metabolic Changes: Impact on Puberty Control

OBJECTIVE

This study aims to explore the significant impact of environmental chemicals on disease development, focusing on their role in developing metabolic and endocrine diseases. The objective is to understand how these chemicals contribute to the increasing prevalence of precocious puberty, considering various factors, including epigenetic changes, lifestyle, and emotional disturbances.

METHODS

The study employs a comprehensive review of descriptive observational studies in both human and animal models to identify a degree of causality between exposure to environmental chemicals and disease development, specifically focusing on endocrine disruption. Due to ethical constraints, direct causation studies in human subjects are not feasible; therefore, the research relies on accumulated observational data.

RESULTS

Puberty is a crucial life period with marked physiological and psychological changes. The age at which sexual characteristics develop is changing in many regions. The findings indicate a correlation between exposure to endocrine-disrupting chemicals and the early onset of puberty. These chemicals have been shown to interfere with normal hormonal processes, particularly during critical developmental stages such as adolescence. The research also highlights the interaction of these chemical exposures with other factors, including nutritional history, social and lifestyle changes, and emotional stress, which together contribute to the prevalence of precocious puberty.

CONCLUSION

Environmental chemicals significantly contribute to the development of certain metabolic and endocrine diseases, particularly in the rising incidence of precocious puberty. Although the evidence is mainly observational, it adequately justifies regulatory actions to reduce exposure risks. Furthermore, these findings highlight the urgent need for more research on the epigenetic effects of these chemicals and their wider impact on human health, especially during vital developmental periods.

Maternal oral exposure to low-dose BPA accelerates the onset of puberty by promoting prepubertal Kiss1 expression in the AVPV nucleus of female offspring

As the incidence of precocious puberty has risen in recent years and the age at puberty onset is younger, children may be at increased risk for health consequences associated with the early onset of puberty. Bisphenol A (BPA) is recognized as an endocrine disruptor chemical that is reported to induce precocious puberty. The effect of BPA exposure modes, times, and doses (especially low dose) were controversial. In the present study, we evaluated the potential effects of maternal exposure to low-dose BPA on the hypothalamus, particularly on the arcuate (ARC) nucleus and anteroventral periventricular (AVPV) nucleus during peri-puberty in offspring of BPA-treated rats. Pregnant rats were exposed to corn oil vehicle, 0.05 mg·kg-1·day-1 BPA, or 5 mg·kg-1·day-1 from gestation day 1 (GD1) to postnatal day 21 (PND21) by daily gavage. Body weight (BW), vaginal opening (VO), ovarian follicular luteinization, and relevant hormone concentrations were measured; hypothalamic Kiss1 and GnRH1 levels by western immunoblot analysis were also assessed as indices of puberty onset. During or after exposure, low-dose BPA restricted BW after birth (at PND1 and PND5), and subsequently accelerated puberty onset by promoting the expression of prepubertal Kiss1 and GnRH1 in the AVPV nucleus on PND30, leading to advanced VO, an elevation in LH and FSH concentrations (on PND30). We also noted increased BW on PND30 and PND35. Maternal oral exposure to low-dose BPA altered the BW curve during the neonatal and peripubertal periods, and subsequently accelerated puberty onset by promoting prepubertal Kiss1 expression in the AVPV nucleus.

Metabolic control of puberty: 60 years in the footsteps of Kennedy and Mitra's seminal work

An individual's nutritional status has a powerful effect on sexual maturation. Puberty onset is delayed in response to chronic energy insufficiency and is advanced under energy abundance. The consequences of altered pubertal timing for human health are profound. Late puberty increases the chances of cardiometabolic, musculoskeletal and neurocognitive disorders, whereas early puberty is associated with increased risks of adult obesity, type 2 diabetes mellitus, cardiovascular diseases and various cancers, such as breast, endometrial and prostate cancer. Kennedy and Mitra's trailblazing studies, published in 1963 and using experimental models, were the first to demonstrate that nutrition is a key factor in puberty onset. Building on this work, the field has advanced substantially in the past decade, which is largely due to the impressive development of molecular tools for experimentation and population genetics. In this Review, we discuss the latest advances in basic and translational sciences underlying the nutritional and metabolic control of pubertal development, with a focus on perspectives and future directions.

Molecular basis of normal and pathological puberty: from basic mechanisms to clinical implications

Puberty is a major maturational event; its mechanisms and timing are driven by genetic determinants, but also controlled by endogenous and environmental cues. Substantial progress towards elucidation of the neuroendocrine networks governing puberty has taken place. However, key aspects of the mechanisms responsible for the precise timing of puberty and its alterations have only recently begun to be deciphered, propelled by epidemiological data suggesting that pubertal timing is changing in humans, via mechanisms that are not yet understood. By integrating basic and clinical data, we provide a comprehensive overview of current advances on the physiological basis of puberty, with a particular focus on the roles of kisspeptins and other central transmitters, the underlying molecular and endocrine mechanisms, and the pathways involved in pubertal modulation by nutritional and metabolic cues. Additionally, we have summarised molecular features of precocious and delayed puberty in both sexes, as revealed by clinical and genetic studies. This Review is a synoptic up-to-date view of how puberty is controlled and of the pathogenesis of major pubertal alterations, from both a clinical and translational perspective. We also highlight unsolved challenges that will seemingly concentrate future research efforts in this active domain of endocrinology.

Overexpression of Brain- and Glial Cell Line-Derived Neurotrophic Factors Is Neuroprotective in an Animal Model of Acute Hypobaric Hypoxia

Currently, the role of the neurotrophic factors BDNF and GDNF in maintaining the brain’s resistance to the damaging effects of hypoxia and functional recovery of neural networks after exposure to damaging factors are actively studied. The assessment of the effect of an increase in the level of these neurotrophic factors in brain tissues using genetic engineering methods on the resistance of laboratory animals to hypoxia may pave the way for the future clinical use of neurotrophic factors BDNF and GDNF in the treatment of hypoxic damage. This study aimed to evaluate the antihypoxic and neuroprotective properties of BDNF and GDNF expression level increase using adeno-associated viral vectors in modeling hypoxia in vivo. To achieve overexpression of neurotrophic factors in the central nervous system’s cells, viral constructs were injected into the brain ventricles of newborn male C57Bl6 (P0) mice. Acute hypobaric hypoxia was modeled on the 30th day after the injection of viral vectors. Survival, cognitive, and mnestic functions in the late post-hypoxic period were tested. Evaluation of growth and weight characteristics and the neurological status of animals showed that the overexpression of neurotrophic factors does not affect the development of mice. It was found that the use of adeno-associated viral vectors increased the survival rate of male mice under hypoxic conditions. The present study indicates that the neurotrophic factors’ overexpression, induced by the specially developed viral constructs carrying the BDNF and GDNF genes, is a prospective neuroprotection method, increasing the survival rate of animals after hypoxic injury.