Fig 1.
Effects of eight-week treatment with NRG1 on serum glucose and insulin levels during OGTT in db/db mice.
Male db/db mice were treated with vehicle (0.9% NaCl; n = 8) or with NRG1 (50 μg.kg-1; n = 8) 3 days/week, for eight weeks. Then, mice fasted for six hours were subjected to glucose tolerance test (GTT) by oral gavage of glucose (2.0 g.kg-1 of body weight). Blood was sampled at 0 (baseline), 30, 60, 90 and 120 minutes for glucose and insulin measurements. A) Changes in serum glucose level during the GTT relative to basal glycemia. B) The net area under the curve (AUC) was calculated for the data presented in A by using the trapezoidal rule. C) Changes in serum insulin concentration during the GTT relative to basal insulinemia. D) The net AUC was calculated for the data presented in C using the trapezoidal rule. Values are the mean ± SEM. VHL: vehicle; NRG1: neuregulin 1; **: p<0.01 compared to VHL.
Fig 2.
A single NRG1 injection lowers serum glucose in db/db mice.
A) Male db/db mice fasted for six hours received an i.p. injection of vehicle (0.9% NaCl; n = 8) or NRG1 (50 μg.kg-1; n = 8) and blood was sampled at different time-points. B) Changes in serum glucose concentration following NRG1 or vehicle injection relative to basal glycemia. C) Net AUC calculated for the data presented in B by using the trapezoidal rule. D) Changes in serum insulin concentration following NRG1 or vehicle injection relative to basal insulinemia. E) Net AUC calculated for the data presented in C using the trapezoidal rule. Values are the mean ± SEM. VHL: vehicle; NRG1: neuregulin 1; **: p<0.01 compared to VHL.
Fig 3.
A single NRG1 injection lowers the serum glucose and insulin responses to OGTT.
A) Six hour-fasted male db/db mice received an i.p. injection of vehicle (0.9% NaCl; n = 8) or NRG1 (50 μg.kg-1; n = 8) fifteen minutes before a glucose load (2.0 g.kg-1 of body weight). Blood was sampled at the time of the NRG1 injection (0; baseline) and then at 15, 45, 75, 105 and 135 minutes post-injection. B) Changes in serum glucose concentration during the oral glucose tolerance test (GTT) relative to basal glycemia. C) Net AUC calculated for the data presented in B using the trapezoidal rule. D) Changes in serum insulin concentration changes at each point of the GTT relative to basal insulinemia. E) Net AUC for the data presented in C calculated using the trapezoidal rule. Values are the mean ± SEM. VHL: vehicle; NRG1: neuregulin 1;*: p<0.05; **: p<0.01 compared to VHL.
Fig 4.
A single NRG1 injection lowers glucose and increases lactatemia during a pyruvate tolerance test.
A) Six hour-fasted male db/db mice received vehicle (0.9% NaCl; n = 8) or NRG1 (50 μg.kg-1; n = 8/group; NRG1) by i.p. injection fifteen minutes before i.p. injection of 1.0g.kg-1 body weight pyruvate. Blood was sampled at the time of the NRG1 injection (0) and then at 15, 45, 75, 105 and 135 minutes post-injection. B) Changes in serum glucose concentration during the pyruvate tolerance test (PTT) relative to basal glycemia. C) Net AUC calculated for the data presented in B using the trapezoidal rule. D) Changes in blood lactate concentration during the PTT relative to basal lactatemia. E) Net AUC calculated for the data presented in D using the trapezoidal rule. Values are the mean ± SEM. VHL: vehicle; NRG1: neuregulin 1;*: p<0.05; **: p<0.01 compared to VHL.
Fig 5.
NRG1 injection activates ERBB3 in the liver but not in the gastrocnemius, WAT and hypothalamus of db/db mice.
Six hour-fasted male db/db mice received an i.p. injection of vehicle (0.9% NaCl; n = 8) or NRG1 (50 μg.kg-1; n = 8) and were euthanized 30 minutes later. A) Western blot analysis using antibodies against total and phosphorylated (p) ERBB3 and ERBB4. ERBB3 and ERBB4 phosphorylation ratios (the ratio between phosphorylated form and total ERBB expression) in B) liver, C) skeletal muscle, D) WAT and E) hypothalamus (relative to controls, VHL). Values are the mean ± SEM. VHL: vehicle; NRG1: neuregulin 1; ***: p<0.001 compared to the VHL group.
Fig 6.
NRG1-induced activation of the AKT and FOXO1 pathways in liver of db/db mice.
Six hour-fasted male db/db mice were treated with vehicle (0.9% NaCl; n = 8) or NRG1 (50 μg.kg-1; n = 8) by i.p. injection and were euthanized 30 minutes later. A) Western blot analysis using antibodies against AKT (total and phosphorylated on Ser473) and FOXO1 (total and phosphorylated on Ser256). Ratios of B) phosphorylated AKT (on Ser473) to total ATK and C) phosphorylated FOXO1 (on Ser256) to total FOXO1. Values shown are mean ± SEM. VHL: vehicle; NRG1: neuregulin 1; ***: p<0.001 compared to the VHL group.