A Study Of Leptin Receptor Levels And Its Correlation With Gestational Diabetes Mellitus

Background:Gestational diabetes mellitus (Gestational Diabetes Mellitus, GDM) is defined as thefirst recognition or onset of carbohydrate intolerance of varying severity during pregnancy,excluding women who exsit diabetes before the pregnancy. GDM has been proved tobe detrimental to the heath of both mother and fetus. While, in addition to insulin, manystudies found that leptin (leptin, Lep) also played an important role in the pathogenesis ofGDM.Leptin can have biological effects through binding with leptin receptor (leptin receptor,LepR). The six subtypes of leptin receptor can be divided into transmembrane leptinreceptors (a, b, c, d, and f) and soluble leptin receptor (e). Transmembrane leptin receptorsare mostly expressed in central and peripheral tissues, primarily involve in the biologicalfunction of leptin. Soluble leptin receptor (sLR), exists in peripheral blood, can regulateleptin biological availability and sensitivity by binding with leptin. Because human sLR isgenerated from the extracellular domain of transmembrane leptin receptors hydrolyzed bymetalloproteinases, so sLR can reflect the expression of transmembrane leptin receptors andthe changes of sLR concentration can be caused by transmembrane leptin receptors.Leptin and transmembrane leptin receptors can be found in the placenta duringpregnancy, and leptin from placenta is the major cause of the increase in maternal serumleptin. The transmembrane leptin receptors of placental can generate sLR by hydrolyzingand cause the increase in seurm sLR along with the pregnancy progress, which can promotebiological activity of leptin and balance the glucose and lipid metabolism during normalpregnancy. But now, the relationship between GDM and the concentration oftransmembrane leptin receptors and/or the sLR is not clear. However, researches ofmetabolic syndrome and type2diabetes show that high leptin concentration, low level ofsLR and obvious leptin resistance exist in obese individuals. And the decrease of serum sLR will increase the risk of type2diabetes. These studies have confirmed that there is amarkedly negative correlation between the level of serum sLR and obesity, leptin resistanceand insulin resistance. Then for GDM mother, whether there is a decrease of serum sLRand/or transmembrane leptin receptors lead to serious leptin resistance or insulin resistanceseriously is not elucidated. Therefore, the purpose of this study is to explore whether thereis a difference between normal and GDM pregnancy from the angle of concentration ofleptin receptors, make a further study of the mechanism of GDM further and providetheoretical basis for the prevention and therapy of GDM.Objective:To find out the characteristics of normal and GDM maternal serum sLR which changesalong with gestational age, then analyze whether there is a relationship between the changesof sLR concentration and the onset of GDM. To study the expression of producer of sLR,-----transmembrane leptin receptors, in placenta and adipose tissue of GDM, thereby revealwhether the anomalies of sLR are associated with GDM and provide a new viewpoint forexploring the pathogenesis of GDM.Methods:1.100cases of normal pregnant women with gestational age of14~19weeks,30~34weeks and full-term before deliver (≧37weeks),20cases of the same gestational ageof GDM pregnant women (excluding other diseases) and20healthy non-pregnant arecollected randomly. The levels of serum sLR in all groups were detected by ELISA(enzyme-linked immunosorbent assay, ELISA). The changes in serum sLR level of normaland GDM pregnant women along with gestational age increasing are analyzed and theserum sLR level of normal pregnancy and GDM in the same gestational age are compared,then we will discuss whether there is a relationship between sLR and GDM.2.We detected the protein and mRNA level of long form of ransmembrane leptinreceptor (OB-Rfl) and short form of transmembrane leptin receptor OB-Rfs) in the placentatissue and adipose tissue of full-term normal and GDM pregnant women by westernblotting and qRT-PCR methods. We may find out whether there is a difference between thetwo groups and speculate that whether transmembrane leptin receptor is associated withGDM, and then go further to confirm the correlation between sLR, which comes fromtransmembrane receptors, with GDM. Results:Experiment Ⅰ:(1)The serum sLR concentrations of normal pregnant women at threedifferent gestational weeks were all notably higher than that of non-pregnant women(P<0.05). And the differences between subgroups are statistically significant (P<0.05),which means the levels of serum sLR are increasing with the progression of pregnancy.(2)The serum sLR levels of GDM were respectively higher than that of non-pregnant women,but the differences were not significant (P>0.05). And within the GDM group, there wereno statistical significant differences among subgroups (P>0.05). But serum sLR levels ofGDM were lower than that of normal in the same gestational week.(3) At four levels ofsLR: a:<4.0ng/ml, b:4.0~7.9ng/ml, c:8.0~11.9ng/ml, d:≧12.0ng/ml, the cases andproportion of GDM were:29(30.53%),20(15.63%),9(13.64%),2(2.82%). Comparedproportion of GDM between every two different sLR concentration, the differences werestatistically significant (P<0.05), except between b and c (P>0.05).The percentage of GDMdecreased with the elevated serum concentration of sLR.Experiment Ⅱ:(1) For both normal and GDM pregnant women, the expression levelsof OB-Rfl and OB-Rfs protein and mRNA in placenta are remarkable higher than that inadipose tissue (P<0.05).(2) Compared with normal pregnancy，the protein and mRNA levelsof OB-Rfl and OB-Rfs were increased markedly in adipose tissue of GDM (P<0.05), whilethe protein and mRNA level of OB-Rfl in placental of GDM were decreased, however, theprotein and mRNA levels of OB-Rfs were increased and there was a significant differencebetween groups (P<0.05).Conclusions:1. The serum sLR concentration of maternal was significantly higher than that ofnon-pregnant women during normal pregnancy, which was increasing along with thepregnancy progress. The serum sLR level of GDM shown no significant difference withthat of non-pregnancy and there was no obviously increase in serum sLR along withgestational age, but it’s significantly lower than normal pregnancy at the same gestationalweeks. There was a strong relationship between the decreasing serum concentration of sLRand the higher morbidity of GDM, which suggested that decrease in sLR may aggravategestational leptin resistance, metabolic disorders and lead to GDM.2. For both full-term normal and GDM pregnant women, the expression of OB-Rfl and OB-Rfs in placenta were significantly higher than that in adipose tissue, which suggestedthat the increased serum sLR might mainly derived from the placental transmembraneleptin receptor. Because of the low concentration of sLR, the GDM pregnant women’sexpression of OB-Rfl and OB-Rfs in adipose tissue was higher than normal pregnantwomen. Particularly, the expression of OB-Rfl was decreased in the placenta of GDMpregnant women, while the expression of OB-Rfs was increased. It confirmed thatdecreasing sLR levels of GDM women was not only related to placental leptin receptorabnormalities, but also related to the activety of metalloproteinase.