Effect of Krüppel-like factor 3 on glucose metabolism

Abstract

Type 2diabetes is an adult-onset condition in which the body is not able to tightly regulate the amount of glucose in the blood and it results from a combination of causes including genetic, behavioral and environmental factors. Krüppel-like factor 3 (KLF3) is a zinc finger transcription factor encoded by the klf3 gene. It has three Krüppel-like zinc fingers that bind to DNA. KLF3 inhibits adipogenesis in vitro through its ability to inhibit an adipogenic master regulator, C/EBPα expression (Sue et al., 2008). klf3-/- mice have fewer and smaller fat cells in adipose tissue. Reasons for different phenotype of the klf3-/- mice than the in vitro results could be prevention of expansion of adipocyte progenitors by premature expression of C/EBPα, likelihood of indirect processes influencing fat pad size in vivo (Sue et al., 2008) and less food intake of klf3-/- mice. klf3-/- mice have increased fasting blood glucose level (Unpublished data, Bell-Anderson Lab). This variation in fasting blood glucose level suggests a role for KLF3 in glucose metabolism. Therefore, this study was designed to investigate the mechanism underlying high fasting blood glucose levels observed in klf3-/- mice. Mice were sacrificed at 13 weeks of age at 5pm in a naturally fasted state and 9pm in a fed state. Blood was collected and blood glucose and plasma glucagon levels were measured. Liver and red quadriceps muscles were collected in order to measure glycogen and glucose-6-phosphatase (G6Pase) activity. Body weight of klf3-/- mice was significantly lighter than that of klf3+/+ mice (p=0.003). We observed that klf3-/- mice had significantly higher fasting blood glucose level than klf3+/+ mice (9.8mmol/L ± 0.89 vs 8.7mmol/L ± 0.71 respectively) (p<0.05). klf3+/+ mice had significantly higher liver glycogen level than KLF3 deficient mice in the fed state (233.47µmol/g ± 54.48 vs 189.68µmol/g ± 38.33 respectively) (p=0.027). There was no significant difference in muscle glycogen levels in klf3-/- and klf3+/+ mice in both fed and fasted states. klf3-/- mice had significantly higher G6Pase activity compared to klf3+/+ mice in the fed state (p=0.008). In the fasted state and fed state, klf3-/- mice had more or less similar G6Pase activities which were respectively 14.1 and 14.9 µmol/g/10 minutes. There was no significant difference in plasma glucagon levels of klf3-/- mice and klf3+/+ mice in the fasted state. Insulin levels unchanged in KLF3 knockout and wild type mice in fed state but KLF3 knockout mice had significantly higher insulin level in fasted state (185.6µU/mL ± 57.5 vs 112.4µU/mL ± 35.7) (p=0.004). Food intake data showed that KLF3 knockout mice eat more food in the afternoon in which we considered as a fasted state. Therefore, the higher fasting blood glucose levels observed in klf3-/- mice is not a result of changes in glycogen levels, G6Pase activity, plasma glucagon and could be due to higher food intake and increased insulin level . Results showed that KLF3 could potentially have an impact on glucose metabolism in the fed and fasted state but further analysis on other glucose metabolic pathways like gluconeogenesis should be performed to confirm the underlying mechanisms for increased fasting blood glucose level of klf3-/- mice.