Science signaling podcast: 21 July 2015

© 2015 American Association for the Advancement of Science. All rights Reserved. This Podcast features an interview with Cristina Murga and Rocio Vila-Bedmar, authors of a Research Article that appears in the 21 July 2015 issue of Science Signaling, about how deleting the kinase GRK2 can counteract some of the metabolic effects of a bad diet. Obesity affects many of the body's normal functions, most notably metabolism. Obesity is associated with insulin resistance and reduced glucose tolerance, which can lead to type 2 diabetes. It also promotes hepatic steatosis, the accumulation of fat in the liver. Vila-Bedmar et al. show that deleting GRK2 can prevent further weight gain and hepatic steatosis and improve glucose sensitivity in obese mice. Deleting GRK2 improved these metabolic consequences of high-fat diet-induced obesity even if the kinase was deleted after the mice had already become obese and resistant to insulin.Peer Reviewe

Downregulation of G protein-coupled receptor kinase 2 levels enhances cardiac insulin sensitivity and switches on cardioprotective gene expression patterns

© 2014 Elsevier B.V. G protein-coupled receptor kinase 2 (GRK2) has recently emerged as a negative modulator of insulin signaling. GRK2 downregulation improves insulin sensitivity and prevents systemic insulin resistance. Cardiac GRK2 levels are increased in human heart failure, while genetically inhibiting GRK2 leads to cardioprotection in mice. However, the molecular basis underlying the deleterious effects of GRK2 up-regulation and the beneficial effects of its inhibition in the heart are not fully understood. Therefore, we have explored the interconnections among a systemic insulin resistant status, GRK2 dosage and cardiac insulin sensitivity in adult (9month-old) animals. GRK2+/- mice display enhanced cardiac insulin sensitivity and mild heart hypertrophy with preserved systolic function. Cardiac gene expression is reprogrammed in these animals, with increased expression of genes related to physiological hypertrophy, while the expression of genes related to pathological hypertrophy or to diabetes/obesity co-morbidities is repressed. Notably, we find that cardiac GRK2 levels increase in situations where insulin resistance develops, such as in ob/ob mice or after high fat diet feeding. Our data suggest that GRK2 downregulation/inhibition can help maintain cardiac function in the face of co-morbidities such as insulin resistance, diabetes or obesity by sustaining insulin sensitivity and promoting a gene expression reprogramming that confers cardioprotection.Ministerio de Educación y Ciencia (SAF2011-23800), Fundación para la Investigación Médica Aplicada (FIMA) and UTE project CIMA, The Cardiovascular Network of Ministerio Sanidad y Consumo-Instituto Carlos III (RD06-0014/0037 and RD12/0042/0012), Comunidad de Madrid (S2010/BMD-2332) and EFSD-Novo Nordisk to F.M and UAM2Grupo Santander to C.M and Wood-Whelan Research Fellowship from IUBMB to E.L. We also acknowledge institutional support from Fundación Ramón Areces.Peer Reviewe

Molecular physiopathology of obesity-related diseases: multi-organ integration by GRK2

Obesity is a worldwide problem that has reached epidemic proportions both in developed and developing countries. The excessive accumulation of fat poses a risk to health since it favours the development of metabolic alterations including insulin resistance and tissue inflammation, which further contribute to the progress of the complex pathological scenario observed in the obese. In this review we put together the different outcomes of fat accumulation and insulin resistance in the main insulin-responsive tissues, and discuss the role of some of the key molecular routes that control disease progression both in an organ-specific and also in a more systemic manner. Particularly, we focus on the importance of studying the integrated regulation of different organs and pathways that contribute to the global pathophysiology of this condition with a specific emphasis on the role of emerging key molecular nodes such as the G protein-coupled receptor kinase 2 (GRK2) signalling hubMinisterio Sanidad y Consumo-Instituto de Salud Carlos III, Spain; Grants SAF2014-55511-R and SAF2012-36400 from Ministerio de Economia y Competitividad (MINECO), Spain (to FM-CM and MS); S2010/BMD-2332 (INDISNET) from Comunidad de Madrid, Spain (to FM); an EFSDNovo Nordisk Grant (to FM) and Fundacion Ramon Areces (to CM and AMB)Peer Reviewe

GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo

© The Author(s).[Background]: Insulin secretion from the pancreatic β-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed. [Results]: Using GRK2 hemizygous mice, isolated pancreatic islets, and model β-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/− mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/− mice. Using nanoBRET in β-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent β-arrestin recruitment. [Conclusions]: Overall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor β-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.We acknowledge support by Ministerio de Economía y Competitividad (MINECO/FEDER), Spain (grant SAF2017-84125-R to FM and CM and BFU2017-89336-R to MV); CIBER de Enfermedades Cardiovasculares (CIBERCV). Instituto de Salud Carlos III, Spain (grant CB16/11/00278 to F.M., co-funded with European FEDER contribution); CIBER de Diabetes y Enfermedades Metabólicas Asociadas (Ciberdem), Instituto de Salud Carlos III (CB07/08/0029 to MV); and Programa de Actividades en Biomedicina de la Comunidad de Madrid-B2017/BMD-3671-INFLAMUNE to FM; Medical Research Council to AT and BJ

G Protein–Coupled Receptor Kinase 2 Plays a Relevant Role in Insulin Resistance and Obesity

OBJECTIVE: Insulin resistance is associated with the pathogenesis of metabolic disorders as type 2 diabetes and obesity. Given the emerging role of signal transduction in these syndromes, we set out to explore the possible role that G protein-coupled receptor kinase 2 (GRK2), first identified as a G protein-coupled receptor regulator, could have as a modulator of insulin responses. RESEARCH DESIGN AND METHODS: We analyzed the influence of GRK2 levels in insulin signaling in myoblasts and adipocytes with experimentally increased or silenced levels of GRK2, as well as in GRK2 hemizygous animals expressing 50% lower levels of this kinase in three different models of insulin resistance: tumor necrosis factor-α (TNF-α) infusion, aging, and high-fat diet (HFD). Glucose transport, whole-body glucose and insulin tolerance, the activation status of insulin pathway components, and the circulating levels of important mediators were measured. The development of obesity and adipocyte size with age and HFD was analyzed. RESULTS: Altering GRK2 levels markedly modifies insulin-mediated signaling in cultured adipocytes and myocytes. GRK2 levels are increased by ∼2-fold in muscle and adipose tissue in the animal models tested, as well as in lymphocytes from metabolic syndrome patients. In contrast, hemizygous GRK2 mice show enhanced insulin sensitivity and do not develop insulin resistance by TNF-α, aging, or HFD. Furthermore, reduced GRK2 levels induce a lean phenotype and decrease age-related adiposity. CONCLUSIONS: Overall, our data identify GRK2 as an important negative regulator of insulin effects, key to the etiopathogenesis of insulin resistance and obesity, which uncovers this protein as a potential therapeutic target in the treatment of these disorders

Cell-Type Specific GRK2 Interactomes: Pathophysiological Implications

G protein-coupled receptor kinase 2 (GRK2) is emerging as a key hub in cell signaling cascades. In addition to modulating activated G protein-coupled receptors, GRK2 can phosphorylate and/or functionally interact with a complex network of cellular proteins in a cell-type and physiological context-dependent way. A combination of such canonical and noncanonical interactions underlies the participation of this kinase in the control of cell migration, proliferation or metabolism and in integrated processes at the tissue or whole organism levels, such as angiogenesis, cardiovascular function, or insulin resistance, among others. Its role as a signaling node and the fact that altered levels of GRK2 are detected in a variety of pathological conditions put forward this protein as a potentially relevant diagnostic and therapeutic targe

Resistencia a insulina en el músculo esquelético: conexión con la obesidad

Insulin resistance is an important contributor to the pathogenesis of type 2 diabetes and obesity is a risk factor for its development, due in part to the fact that adipose tissue secretes proteins called adipokines that may influence insulin sensitivity. Among these molecules, TNFa has been proposed as a link between obesity and insulin resistance because TNFa is overexpressed in adipose tissues of obese animals and humans, and obese mice lacking either TNFa or its receptor show protection for developing insulin resistance. The direct exposure to TNFa induced a state of insulin resistance on glucose uptake in myocytes and brown adipocytes, due to the activation of pro-inflammatory pathways that impair insulin-signaling at the level of the IRS proteins. In this regard the residue Ser307 in IRS-1 has been identified as a site for TNFa-inhibitory effects in myotubes, with being p38MAPK and IKK involved in the phosphorylation of this residue. Conversely, serine phosphorylation of IRS-2 mediated by TNFa activation of MAPKs was the mechanism found in brown adipocytes. The phosphatase PTP1B acts as a physiological negative regulator of insulin signaling by dephosphorylating the phosphotyrosine residues of the insulin receptor and IRS-1, and PTP1B expression is increased in muscle and white adipose tissue of obese and diabetic humans and rodents. Moreover, up-regulation of PTP1B expression has recently been found in cells treated with TNFa. Accordingly, myocytes and primary brown adipocytes deficient on PTP1B are protected against insulin resistance by this cytokine. Furthermore, down-regulation of PTP1B activity is also possible by the use of pharmacological agonists of nuclear receptors that restored insulin sensitivity in the presence of TNFa. In conclusion, the lack of PTP1B in muscle and brown adipocytes increase insulin sensitivity and glucose uptake and could confer protection against insulin resistance induced by adipokines.Key Words: Glucose uptake, LXR, PTP1B, TNFa, IL-6.Entre las complicaciones asociadas a la Obesidad, tiene una especial relevancia el desarrollo de resistencia a la insulina, siendo el primer eslabón de una amplia patología conocida como diabetes tipo 2. La Obesidad se considera como un estado crónico de inflamación de baja intensidad, como indican los niveles circulantes elevados de moléculas proinflamatorias. Se ha propuesto al TNFa como el nexo de unión entre adiposidad y desarrollo de resistencia a insulina ya que la mayoría de los pacientes con diabetes tipo 2 son obesos y tienen aumentada la expresión de TNFa en sus adipocitos, y los animales obesos deleccionados para la función del TNFa o su receptor no desarrollan resistencia a insulina. Las citocinas proinflamatorias producidas por los adipocitos y/o macrófagos activan quinasas de estrés, proinflamatorias y factores de transcripción que actúan sobre los tejidos periféricos (entre ellos el músculo y el propio tejido adiposo) produciendo resistencia a la acción de la insulina, que es un defecto en la señalización a varios niveles. En concreto, el TNFa activa la quinasa p38MAPK que fosforila en residuos de serina a los IRSs, bloqueando su fosforilación en tirosina en respuesta a la insulina, tanto en adipocitos marrones como en miocitos. Muy recientemente hemos observado que la fosfatasa PTP1B también está implicada en la resistencia a insulina por TNFa en ambos modelos. En la clínica se está utilizando actualmente el tratamiento con tiazolidindionas en pacientes con diabetes tipo 2. Otros agonistas de receptores nucleares empiezan a aparecer en la bibliografía como potenciales sensibilizadores a acción de la insulina, entre ellos el LXR, que puede antagonizar la señalización proinflamatoria en los propios adipocitos y/o en el músculo.Palabras clave: Transporte de glucosa, LXR, PTP1B, TNFa, IL-6

Skeletal muscle myogenesis is regulated by G protein-coupled receptor kinase 2

This is a pre-copyedited, author-produced pdf of an article accepted for publication in Journal of Molecular Cell Biology following peer review. The version of record Journal of Molecular Cell Biology 6.4 (2014) is available online at: http://dx.doi.org/10.1093/jmcb/mju025G protein-coupled receptor kinase 2 (GRK2) is an important serine/threonine-kinase regulating different membrane receptors and intracellular proteins. Attenuation of Drosophila Gprk2 in embryos or adult flies induced a defective differentiation of somatic muscles, loss of fibers, and a flightless phenotype. In vertebrates, GRK2 hemizygous mice contained less but more hypertrophied skeletal muscle fibers than wild-type littermates. In C2C12 myoblasts overexpression of a GRK2 kinase-deficient mutant (K220R) caused precocious differentiation of cells into immature myotubes, which were wider in size and contained more fused nuclei, while GRK2 overexpression blunted differentiation. Moreover, p38MAPK and Akt pathways were activated at an earlier stage and to a greater extent in K220R-expressing cells or upon kinase downregulation, while the activation of both kinases was impaired in GRK2- overexpressing cells. The impaired differentiation and fewer fusion events promoted by enhanced GRK2 levels were recapitulated by a p38MAPK mutant, which was able to mimic the inhibitory phosphorylation of p38MAPK by GRK2, whereas the blunted differentiation observed in GRK2-expressing clones was rescued in the presence of a constitutively active upstream stimulator of the p38MAPK pathway. These results suggest that balanced GRK2 function is necessary for a timely and complete myogenic process.This work was supported by Grants BFU2008-04043 (to M.L. and S.F.-V.), SAF2012-3618 (to S.F.-V.), and SAF2011-23800 (to F.M.) from Ministerio de Economía y Competitividad, Spain; S2010/BMD-2332 (INDISNET) from Comunidad de Madrid, Spain (to F.M.); CIBER de Diabetes y Enfermedades Metabólicas Asociadas and The Cardiovascular Network (RD06- 0014/0037 and RD12/0042/0012) from Ministerio Sanidad y Consumo-Instituto Carlos III, Spain (to F.M.); UAM-Banco de Santander (to C.M.); BFU2010-14884 (to M.R.-G.). S.F.-V. is recipient of a ‘Miguel Servet’ tenure track program (CP10/00438) co-financed by the European Regional Development Fund (ERDF). We also acknowledge the support of COST Action BM0602 from the European Commission (to M.L.) and institutional support from Fundación Ramón Arece

Downregulation of G protein-coupled receptor kinase 2 levels enhances cardiac insulin sensitivity and switches on cardioprotective gene expression patterns

G protein-coupled receptor kinase 2 (GRK2) has recently emerged as a negative modulator of insulin signalling. GRK2 downregulation improves insulin sensitivity and prevents systemic insulin resistance (IR). Cardiac GRK2 levels are increased in 5 human heart failure, while genetically inhibiting GRK2 leads to cardioprotection in mice. However, the molecular basis underlying the 6 deleterious effects of GRK2 up-regulation and the beneficial effects of its inhibition in the heart are not fully understood. Therefore, 7 we have explored the interconnections among a systemic IR status, GRK2 dosage and cardiac insulin sensitivity in adult (9 month-old) animals. GRK2+/- mice display enhanced cardiac insulin sensitivity and mild heart hypertrophy with preserved systolic function. Cardiac gene expression is reprogrammed in these animals, with increased expression of genes related to physiological hypertrophy, while the expression of genes related to pathological hypertrophy or to diabetes/obesity co-morbidities is repressed. Notably, we find that cardiac GRK2 levels increase in situations where IR develops, such as in ob/ob mice or after high fat diet feeding. Our data suggest that GRK2 downregulation/inhibition can help maintain cardiac function in the face of co-morbidities such as IR, diabetes or obesity by sustaining insulin sensitivity and promoting a gene expression reprogramming that confers cardioprotection.Grants from Ministerio de Educación y Ciencia (SAF2011-23800), Fundación para la Investigación Médica Aplicada (FIMA) and UTE project CIMA, The Cardiovascular Network of Ministerio Sanidad y Consumo-Instituto Carlos III (RD06-0014/0037 and RD12/0042/0012), Comunidad de Madrid (S2010/BMD-2332) and EFSD-Novo Nordisk to F.M and UAM Grupo Santander to C.M and Wood-Whelan Research Fellowship from IUBMB to E.L. We also acknowledge institutional support from Fundación Ramón Arece