To explore the physiological functions of endothelin-2 (ET-2), we generated gene-targeted mouse models. Global
Inik Chang, Alexa N. Bramall, Amy Greenstein Baynash, Amir Rattner, Dinesh Rakheja, Martin Post, Stephen Joza, Colin McKerlie, Duncan J. Stewart, Roderick R. McInnes, Masashi Yanagisawa
Type II deiodinase (D2) activates thyroid hormone by converting thyroxine (T4) to 3,5,3′-triiodothyronine (T3). This allows plasma T4 to signal a negative feedback loop that inhibits production of thyrotropin-releasing hormone (TRH) in the mediobasal hypothalamus (MBH) and thyroid-stimulating hormone (TSH) in the pituitary. To determine the relative contributions of these D2 pathways in the feedback loop, we developed 2 mouse strains with pituitary- and astrocyte-specific
Tatiana L. Fonseca, Mayrin Correa-Medina, Maira P.O. Campos, Gabor Wittmann, Joao P. Werneck-de-Castro, Rafael Arrojo e Drigo, Magda Mora-Garzon, Cintia Bagne Ueta, Alejandro Caicedo, Csaba Fekete, Balazs Gereben, Ronald M. Lechan, Antonio C. Bianco
Type 2 diabetes (T2D) has emerged as a major threat to human health in most parts of the world. Therapeutic strategies aimed at improving pancreatic β cell function are predicted to prove beneficial for the treatment of T2D. In the present study, we demonstrate that drug-mediated, chronic, and selective activation of β cell Gq signaling greatly improve β cell function and glucose homeostasis in mice. These beneficial metabolic effects were accompanied by the enhanced expression of many genes critical for β cell function, maintenance, and differentiation. By employing a combination of in vivo and in vitro approaches, we identified a novel β cell pathway through which receptor-activated Gq leads to the sequential activation of ERK1/2 and IRS2 signaling, thus triggering a series of events that greatly improve β cell function. Importantly, we found that chronic stimulation of a designer Gq-coupled receptor selectively expressed in β cells prevented both streptozotocin-induced diabetes and the metabolic deficits associated with the consumption of a high-fat diet in mice. Since β cells are endowed with numerous receptors that mediate their cellular effects via activation of Gq-type G proteins, our findings provide a rational basis for the development of novel antidiabetic drugs targeting this class of receptors.
Shalini Jain, Inigo Ruiz de Azua, Huiyan Lu, Morris F. White, Jean-Marc Guettier, Jürgen Wess
Insulin-secreting β cells and glucagon-secreting α cells maintain physiological blood glucose levels, and their malfunction drives diabetes development. Using ChIP sequencing and RNA sequencing analysis, we determined the epigenetic and transcriptional landscape of human pancreatic α, β, and exocrine cells. We found that, compared with exocrine and β cells, differentiated α cells exhibited many more genes bivalently marked by the activating H3K4me3 and repressing H3K27me3 histone modifications. This was particularly true for β cell signature genes involved in transcriptional regulation. Remarkably, thousands of these genes were in a monovalent state in β cells, carrying only the activating or repressing mark. Our epigenomic findings suggested that α to β cell reprogramming could be promoted by manipulating the histone methylation signature of human pancreatic islets. Indeed, we show that treatment of cultured pancreatic islets with a histone methyltransferase inhibitor leads to colocalization of both glucagon and insulin and glucagon and insulin promoter factor 1 (PDX1) in human islets and colocalization of both glucagon and insulin in mouse islets. Thus, mammalian pancreatic islet cells display cell-type–specific epigenomic plasticity, suggesting that epigenomic manipulation could provide a path to cell reprogramming and novel cell replacement-based therapies for diabetes.
Nuria C. Bramswig, Logan J. Everett, Jonathan Schug, Craig Dorrell, Chengyang Liu, Yanping Luo, Philip R. Streeter, Ali Naji, Markus Grompe, Klaus H. Kaestner
Klotho is a potent regulator of 1,25-hydroxyvitamin D3 [1,25(OH)2D3] formation and calcium-phosphate metabolism. Klotho-hypomorphic mice (
Jakob Voelkl, Ioana Alesutan, Christina B. Leibrock, Leticia Quintanilla-Martinez, Volker Kuhn, Martina Feger, Sobuj Mia, Mohamed S.E. Ahmed, Kevin P. Rosenblatt, Makoto Kuro-o, Florian Lang
Thyroid hormone is well known for its profound direct effects on cardiovascular function and metabolism. Recent evidence, however, suggests that the hormone also regulates these systems indirectly through the central nervous system. While some of the molecular mechanisms underlying the hormone’s central control of metabolism have been identified, its actions in the central cardiovascular control have remained enigmatic. Here, we describe a previously unknown population of parvalbuminergic neurons in the anterior hypothalamus that requires thyroid hormone receptor signaling for proper development. Specific stereotaxic ablation of these cells in the mouse resulted in hypertension and temperature-dependent tachycardia, indicating a role in the central autonomic control of blood pressure and heart rate. Moreover, the neurons exhibited intrinsic temperature sensitivity in patch-clamping experiments, providing a new connection between cardiovascular function and core temperature. Thus, the data identify what we believe to be a novel hypothalamic cell population potentially important for understanding hypertension and indicate developmental hypothyroidism as an epigenetic risk factor for cardiovascular disorders. Furthermore, the findings may be beneficial for treatment of the recently identified patients that have a mutation in thyroid hormone receptor α1.
Jens Mittag, David J. Lyons, Johan Sällström, Milica Vujovic, Susi Dudazy-Gralla, Amy Warner, Karin Wallis, Anneke Alkemade, Kristina Nordström, Hannah Monyer, Christian Broberger, Anders Arner, Björn Vennström
The FGF23 coreceptor αKlotho (αKL) is expressed as a membrane-bound protein (mKL) that forms heteromeric complexes with FGF receptors (FGFRs) to initiate intracellular signaling. It also circulates as an endoproteolytic cleavage product of mKL (cKL). Previously, a patient with increased plasma cKL as the result of a translocation [t(9;13)] in the αKLOTHO (KL) gene presented with rickets and a complex endocrine profile, including paradoxically elevated plasma FGF23, despite hypophosphatemia. The goal of this study was to test whether cKL regulates phosphate handling through control of FGF23 expression. To increase cKL levels, mice were treated with an adeno-associated virus producing cKL. The treated groups exhibited dose-dependent hypophosphatemia and hypocalcemia, with markedly elevated FGF23 (38 to 456 fold). The animals also manifested fractures, reduced bone mineral content, expanded growth plates, and severe osteomalacia, with highly increased bone Fgf23 mRNA (>150 fold). cKL activity in vitro was specific for interactions with FGF23 and was FGFR dependent. These results demonstrate that cKL potently stimulates FGF23 production in vivo, which phenocopies the KL translocation patient and metabolic bone syndromes associated with elevated FGF23. These findings have important implications for the regulation of αKL and FGF23 in disorders of phosphate handling and biomineralization.
Rosamund C. Smith, Linda M. O’Bryan, Emily G. Farrow, Lelia J. Summers, Erica L. Clinkenbeard, Jessica L. Roberts, Taryn A. Cass, Joy Saha, Carol Broderick, Y. Linda Ma, Qing Qiang Zeng, Alexei Kharitonenkov, Jonathan M. Wilson, Qianxu Guo, Haijun Sun, Matthew R. Allen, David B. Burr, Matthew D. Breyer, Kenneth E. White
Hyperprolactinemia is the most common cause of hypogonadotropic anovulation and is one of the leading causes of infertility in women aged 25–34. Hyperprolactinemia has been proposed to block ovulation through inhibition of GnRH release. Kisspeptin neurons, which express prolactin receptors, were recently identified as major regulators of GnRH neurons. To mimic the human pathology of anovulation, we continuously infused female mice with prolactin. Our studies demonstrated that hyperprolactinemia in mice induced anovulation, reduced GnRH and gonadotropin secretion, and diminished kisspeptin expression. Kisspeptin administration restored gonadotropin secretion and ovarian cyclicity, suggesting that kisspeptin neurons play a major role in hyperprolactinemic anovulation. Our studies indicate that administration of kisspeptin may serve as an alternative therapeutic approach to restore the fertility of hyperprolactinemic women who are resistant or intolerant to dopamine agonists.
Charlotte Sonigo, Justine Bouilly, Nadège Carré, Virginie Tolle, Alain Caraty, Javier Tello, Fabian-Jesus Simony-Conesa, Robert Millar, Jacques Young, Nadine Binart
Botulinum neurotoxins (BoNTs) are zinc endopeptidases that block release of the neurotransmitter acetylcholine in neuromuscular synapses through cleavage of soluble N-ethylmaleimide-sensitive fusion (NSF) attachment protein receptor (SNARE) proteins, which promote fusion of synaptic vesicles to the plasma membrane. We designed and tested a BoNT-derived targeted secretion inhibitor (TSI) targeting pituitary somatotroph cells to suppress growth hormone (GH) secretion and treat acromegaly. This recombinant protein, called SXN101742, contains a modified GH-releasing hormone (GHRH) domain and the endopeptidase domain of botulinum toxin serotype D (GHRH-LHN/D, where HN/D indicates endopeptidase and translocation domain type D). In vitro, SXN101742 targeted the GHRH receptor and depleted a SNARE protein involved in GH exocytosis, vesicle-associated membrane protein 2 (VAMP2). In vivo, administering SXN101742 to growing rats produced a dose-dependent inhibition of GH synthesis, storage, and secretion. Consequently, hepatic IGF1 production and resultant circulating IGF1 levels were reduced. Accordingly, body weight, body length, organ weight, and bone mass acquisition were all decreased, reflecting the biological impact of SXN101742 on the GH/IGF1 axis. An inactivating 2–amino acid substitution within the zinc coordination site of the endopeptidase domain completely abolished SXN101742 inhibitory actions on GH and IGF1. Thus, genetically reengineered BoNTs can be targeted to nonneural cells to selectively inhibit hormone secretion, representing a new approach to treating hormonal excess.
Emmanuel Somm, Nicolas Bonnet, Alberto Martinez, Philip M.H. Marks, Verity A. Cadd, Mark Elliott, Audrey Toulotte, Serge L. Ferrari, René Rizzoli, Petra S. Hüppi, Elaine Harper, Shlomo Melmed, Richard Jones, Michel L. Aubert
Chronic kidney disease–mineral and bone disorder (CKD-MBD) is associated with secondary hyperparathyroidism (HPT) and serum elevations in the phosphaturic hormone FGF23, which may be maladaptive and lead to increased morbidity and mortality. To determine the role of FGF23 in the pathogenesis of CKD-MBD and development of secondary HPT, we developed a monoclonal FGF23 antibody to evaluate the impact of chronic FGF23 neutralization on CKD-MBD, secondary HPT, and associated comorbidities in a rat model of CKD-MBD. CKD-MBD rats fed a high-phosphate diet were treated with low or high doses of FGF23-Ab or an isotype control antibody. Neutralization of FGF23 led to sustained reductions in secondary HPT, including decreased parathyroid hormone, increased vitamin D, increased serum calcium, and normalization of bone markers such as cancellous bone volume, trabecular number, osteoblast surface, osteoid surface, and bone-formation rate. In addition, we observed dose-dependent increases in serum phosphate and aortic calcification associated with increased risk of mortality in CKD-MBD rats treated with FGF23-Ab. Thus, mineral disturbances caused by neutralization of FGF23 limited the efficacy of FGF23-Ab and likely contributed to the increased mortality observed in this CKD-MBD rat model.
Victoria Shalhoub, Edward M. Shatzen, Sabrina C. Ward, James Davis, Jennitte Stevens, Vivian Bi, Lisa Renshaw, Nessa Hawkins, Wei Wang, Ching Chen, Mei-Mei Tsai, Russell C. Cattley, Thomas J. Wronski, Xuechen Xia, Xiaodong Li, Charles Henley, Michael Eschenberg, William G. Richards