Differentiated Mouse Adipocytes in Primary Culture: A Model of Insulin Resistance

Insulin resistance is a reduced effect of insulin on its target cells, usually derived from decreased insulin receptor signaling. Insulin resistance ...

Universidad Nacional Autónoma de México (UNAM)

The levels of the hormone prolactin (PRL) are reduced in the circulation of patients with Type 2 diabetes and in obese children, and lower systemic PRL levels correlate with an increased prevalence of diabetes and a higher risk of metabolic syndrome. The secretion of anterior pituitary (AP) PRL in metabolic diseases may be influenced by the interplay between transforming growth factor β (TGF-β) and tumor necrosis factor α (TNF-α), which inhibit and can stimulate AP PRL synthesis, respectively, and are known contributors to insulin resistance and metabolic complications. Here, we show that TGF-β and TNF-α antagonize the effect of each other on the expression and release of PRL by the GH4C1 lactotrope cell line. The levels of AP mRNA and circulating PRL decrease in high-fat diet-induced obese rats in parallel with increased and reduced AP levels of TGF-β and TNF-α mRNA, respectively. Likewise, AP expression and circulating levels of PRL are reduced in streptozotocin-induced diabetic rats and are associated with higher AP expression and protein levels of TGF-β and TNF-α. The opposing effects of the two cytokines on cultured AP cells, together with their altered expression in the AP of obese and diabetic rats suggest they are linked to the reduced PRL production and secretion characteristics of metabolic diseases.

Prolactin anterior pituitary expression and circulating levels are reduced in obese and diabetic rats: role of TGF-β and TNF-α.

The identification of pathways necessary for retinal pigment epithelium (RPE) function is fundamental to uncover therapies for blindness. Prolactin (PRL) receptors are expressed in the retina, but nothing is known about the role of PRL in RPE. Using the adult RPE 19 (ARPE-19) human cell line and mouse RPE, we identified the presence of PRL receptors and demonstrated that PRL is necessary for RPE cell survival via anti-apoptotic and antioxidant actions. PRL promotes the antioxidant capacity of ARPE-19 cells by reducing glutathione. It also blocks the hydrogen peroxide-induced increase in deacetylase sirtuin 2 (SIRT2) expression, which inhibits the TRPM2-mediated intracellular Ca(2+) rise associated with reduced survival under oxidant conditions. RPE from PRL receptor-null (prlr(-/-)) mice showed increased levels of oxidative stress, Sirt2 expression and apoptosis, effects that were exacerbated in animals with advancing age. These observations identify PRL as a regulator of RPE homeostasis.

Prolactin protects retinal pigment epithelium by inhibiting sirtuin 2-dependent cell death.

Excessive accumulation of body fat triggers insulin resistance and features of the metabolic syndrome. Recently, evidence has accumulated that obesity, type 2 diabetes, and metabolic syndrome are associated with reduced levels of serum prolactin (PRL) in humans and rodents, raising the question of whether low PRL levels contribute to metabolic dysfunction. Here, we have addressed this question by investigating the role of PRL in insulin sensitivity and adipose tissue fitness in obese rodents and humans. In diet-induced obese rats, treatment with PRL delivered via osmotic mini-pumps, improved insulin sensitivity, prevented adipocyte hypertrophy, and reduced inflammatory cytokine expression in visceral fat. PRL also induced increased expression of Pparg and Xbp1s in visceral adipose tissue and elevated circulating adiponectin levels. Conversely, PRL receptor null mice challenged with a high-fat diet developed greater insulin resistance, glucose intolerance, and increased adipocyte hypertrophy compared with wild-type mice. In humans, serum PRL values correlated positively with systemic adiponectin levels and were reduced in insulin-resistant patients. Furthermore, PRL circulating levels and PRL produced by adipose tissue correlated directly with the expression of PPARG, ADIPOQ, and GLUT4 in human visceral and sc adipose tissue. Thus, PRL, acting through its cognate receptors, promotes healthy adipose tissue function and systemic insulin sensitivity. Increasing the levels of PRL in the circulation may have therapeutic potential against obesity-induced metabolic diseases.

Prolactin Promotes Adipose Tissue Fitness and Insulin Sensitivity in Obese Males.

The liver grows during the early postnatal period first at slower and then at faster rates than the body to achieve the adult liver-to-body weight ratio (LBW), a constant reflecting liver health. The hormone prolactin (PRL) stimulates adult liver growth and regeneration, and its levels are high in the circulation of newborn infants, but whether PRL plays a role in neonatal liver growth is unknown. Here, we show that the liver produces PRL and upregulates the PRL receptor in mice during the first 2 wk after birth, when liver growth lags behind body growth. At postnatal week 4, the production of PRL by the liver ceases coinciding with the elevation of circulating PRL and the faster liver growth that catches up with body growth. PRL receptor null mice ( Prlr-/-) show a significant decrease in the LBW at 1, 4, 6, and 10 postnatal weeks and reduced liver expression of proliferation [cyclin D1 ( Ccnd1)] and angiogenesis [platelet/endothelial cell adhesion molecule 1 ( Pecam1)] markers relative to Prlr+/+ mice. However, the LBW increases in Prlr-/- mice at postnatal week 2 concurring with the enhanced liver expression of Igf-1 and the liver upregulation and downregulation of suppressor of cytokine signaling 2 ( Socs2) and Socs3, respectively. These findings indicate that PRL acts locally and systemically to restrict and stimulate postnatal liver growth. PRL inhibits liver and body growth by attenuating growth hormone-induced Igf-1 liver expression via Socs2 and Socs3-related mechanisms.

Prolactin regulates liver growth during postnatal development in mice.

Vasoinhibin, a protein derived from prolactin, regulates various vascular functions including endothelial cell survival. Of note, vasoinhibin is present in the central nervous system, where it triggers neuroendocrine and behavioral responses to stress. Moreover, vasoinhibin compromises nerve growth factor (NGF)-induced neurite outgrowth in primary sensory neurons of the peripheral nervous system. Nonetheless, information on the functions of vasoinhibin in developing neurons remains limited. The present study explored whether vasoinhibin affects the neurotrophic actions of NGF by measuring the cell differentiation and survival of PC12 pheochromocytoma cells.

Vasoinhibin Suppresses Nerve Growth Factor-Induced Differentiation and Survival of PC12 Pheochromocytoma Cells.

Low prolactin (PRL) serum levels are associated with glucose intolerance and type 2 diabetes in adults, and with metabolic syndrome and obesity in children. In obese rodents, PRL treatment promotes insulin sensitivity by maintaining adipose tissue fitness, and lack of PRL signaling exacerbates obesity-derived metabolic alterations. Since adipose tissue dysfunction is a key factor triggering metabolic alterations, we evaluated whether PRL serum levels are associated with adipocyte hypertrophy (a marker of adipose tissue dysfunction), insulin resistance, and metabolic syndrome in lean, overweight, and obese adult men and women.

Low prolactin levels are associated with visceral adipocyte hypertrophy and insulin resistance in humans.

Prolactin (PRL) levels are reduced in the circulation of rats with diabetes or obesity, and lower circulating levels of PRL correlate with increased prevalence of diabetes and a higher risk of metabolic alterations in the clinic. Furthermore, PRL stimulates β-cell proliferation, survival, and insulin production and pregnant mice lacking PRL receptors in β-cells develop gestational diabetes. To investigate the protective effect of endogenous PRL against diabetes outside pregnancy, we compared the number of cases and severity of streptozotocin (STZ)-induced hyperglycemia between C57BL/6 mice null for the PRL receptor gene ( ) and wild-type mice ( ). STZ-treated diabetic  mice showed a higher number of cases and later recovery from hyperglycemia, exacerbated glucose levels, and glucose intolerance compared to the  mice counterparts. Consistent with the worsening of hyperglycemia, pancreatic islet density, β-cell number, proliferation, and survival, as well as circulating insulin levels were reduced, whereas α-cell number and pancreatic inflammation were increased in the absence of PRL signaling. Deletion of the PRL receptor did not alter the metabolic parameters in vehicle-treated animals. We conclude that PRL protects whole body glucose homeostasis by reducing β-cell loss and pancreatic inflammation in STZ-induced diabetes. Medications elevating PRL circulating levels may prove to be beneficial in diabetes.

Global Deletion of the Prolactin Receptor Aggravates Streptozotocin-Induced Diabetes in Mice.

Excessive vasopermeability and angiogenesis compromise vision in diabetic macular oedema (DME) and diabetic retinopathy (DR). Vasoinhibin is a fragment of the hormone prolactin (PRL) that inhibits diabetes-induced retinal hypervasopermeability and ischaemia-induced retinal angiogenesis in rodents. Hyperprolactinaemia generated by the dopamine D2 receptor antagonist, levosulpiride, is associated with higher levels of vasoinhibin in the vitreous of patients with DR, implying a beneficial outcome due to vasoinhibin-mediated inhibition of retinal vascular alterations. Here, we tested whether hyperprolactinaemia induced by racemic sulpiride increases intraocular vasoinhibin levels and inhibits retinal hypervasopermeability in diabetic rats. Diabetes was generated with streptozotocin and, 4 weeks later, rats were treated for 2 weeks with sulpiride or osmotic minipumps delivering PRL. ELISA, Western blot, and Evans blue assay were used to evaluate serum PRL, retinal vasoinhibin, and retinal vasopermeability, respectively. Hyperprolactinaemia in response to sulpiride or exogenous PRL was associated with increased levels of vasoinhibin in the retina and reduced retinal hypervasopermeability. Furthermore, sulpiride decreased retinal haemorrhages in response to the intravitreal administration of vascular endothelial growth factor (VEGF). Neither sulpiride nor exogenous PRL modified blood glucose levels or bodyweight. We conclude that sulpiride-induced hyperprolactinaemia inhibits the diabetes- and VEGF-mediated increase in retinal vasopermeability by promoting the intraocular conversion of endogenous PRL to vasoinhibin. These findings support the therapeutic potential of sulpiride and its levorotatory enantiomer, levosulpiride, against DME and DR.

Sulpiride-induced hyperprolactinaemia increases retinal vasoinhibin and protects against diabetic retinopathy in rats.

The role of prolactin (PRL) favoring metabolic homeostasis is supported by multiple preclinical and clinical studies. PRL levels are key to explaining the direction of its actions. In contrast with the negative outcomes associated with very high (>100 μg/L) and very low (<7 μg/L) PRL levels, moderately high PRL levels, both within but also above the classically considered physiological range are beneficial for metabolism and have been defined as HomeoFIT-PRL. In animal models, HomeoFIT-PRL levels counteract insulin resistance, glucose intolerance, adipose tissue hypertrophy and fatty liver; and in humans associate with reduced prevalence of insulin resistance, fatty liver, glucose intolerance, metabolic syndrome, reduced adipocyte hypertrophy, and protection from type 2 diabetes development. The beneficial actions of PRL can be explained by its positive effects on main metabolic organs including the pancreas, liver, adipose tissue, and hypothalamus. Here, we briefly review work supporting PRL as a promoter of metabolic homeostasis in rodents and humans, the PRL levels associated with metabolic protection, and the proposed mechanisms involved. Finally, we discuss the possibility of using drugs elevating PRL for the treatment of metabolic diseases.

The beneficial metabolic actions of prolactin.

Obesity is a modern pandemic with negative consequences in women's reproductive health. Women with overweight and obesity can develop mammary gland alterations that unable exclusive breastfeeding. Obesity associates with a disturbed lactating mammary gland endocrine environment including a decreased action of the hormone prolactin (PRL), the master regulator of lactation. The PRL receptor and the action of PRL are reduced in the mammary gland of lactating rodents fed an obesogenic diet and are contributing factors to impaired lactation in obesity. Also, treatment with PRL improves milk yield in women with lactation insufficiency. This review focuses on the impact of diet-induced obesity in the lactating mammary gland and how obesity impairs the lactogenic action of PRL. Although obesity alters lactation performance in humans and rodents, the responsible mechanisms have been mainly addressed in rodents.

Xarubet Ruiz-Herrera

Instituto de Neurobiología

Universidad Nacional Autónoma de México (UNAM)

Differentiated Mouse Adipocytes in Primary Culture: A Model of Insulin Resistance

Xarubet Ruiz-Herrera

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Instituto de Neurobiología

Universidad Nacional Autónoma de México (UNAM)

Differentiated Mouse Adipocytes in Primary Culture: A Model of Insulin Resistance

Instituto de Neurobiología