The role of FKBPL in diabetes and associated cardiovascular health

Abstract

Diabetes is becoming an epidemic disease of global proportions with an estimated 422 million people living with the condition. Cardiovascular diseases (CVD) are the leading cause of death globally with the incidence three-fold higher in people with diabetes. Furthermore, cardiovascular complication of pregnancy, pre-eclampsia, is also associated with up to four-fold increased risk in women with diabetes. Pre-eclampsia is also the leading cause of death in pregnancy and is associated with increased incidence of CVD later in life. Although underlying mechanisms linking diabetes with CVD both in pregnancy and beyond are not very well understood, aberrant angiogenesis and endothelial dysfunction have been closely implicated. FKBPL is a novel antiangiogenic protein which has a critical role in physiological and pathological angiogenesis. While FKBPL homozygous knockout (Fkbpl-/-) mice showed embryonic lethality, FKBPL knockdown (Fkbpl+/-) mice were viable and developed normally but showed signs of vascular dysfunction and leakage. The role of FKBPL in regulating angiogenesis has been demonstrated in other diseases such as cancer, however its role in diabetes and CVD is unknown. Therefore, the main aims of this thesis were to: 1) investigate the role of FKBPL on endothelial function in the presence of diabetes in vitro, 2) elucidate the metabolic and vascular function of FKBPL in experimental model of diabetes in vivo, and 3) investigate the role of placental FKBPL in pregnancies complicated by diabetes or pre-eclampsia. Our in vitro data demonstrated that FKBPL knockdown in endothelial cells under baseline conditions was associated with abnormal expression of proteins which have important roles in endothelial function, such as ICAM-1, VE-cadherin and eNOS. Functional assays showed that low FKBPL levels are associated with impaired endothelial barrier formation, response to stress and increased angiogenesis, whilst the opposite effect was demonstrated with FKBPL overexpression. Furthermore, FKBPL overexpression in hypoxia (1%) reduced angiogenesis to normoxic levels. Moreover, FKBPL overexpression in normal glucose conditions was found to induce several miRNAs which regulate pro-inflammatory pathways. Conversely, overexpression of FKBPL in high glucose conditions downregulated miRNAs which were reported to reduce inflammation. Subsequently, FKBPL transgenic mice with superimposed diabetes via streptozocin (STZ) injection were used to assess the effects of low FKBPL levels on metabolic, cardiac and vascular function. Low FKBPL levels at baseline led to significant weight gain in association with signs of left ventricular hypertrophy, vascular dysfunction and increased inflammation. In diabetes, although glucose metabolism was impaired in association with low FKBPL levels, markers of vascular function were improved as well as reduction in cardiac inflammation. In terms of high-risk pregnancies, placental FKBPL expression was increased in pregnant women who developed pre-eclampsia in association with reduced levels of other pro-angiogenic factors which are essential for placenta development. On the other hand, FKBPL was downregulated in ACH-3P trophoblast (foetal) cells, important for placental development, under low oxygen concentration (2.5%) and by high glucose (25 mM), but only under low oxygen conditions (6.5% and 2.5%). Furthermore, placental FKBPL expression was reduced in pregnant women with pre-existing diabetes or gestational diabetes in association with increased levels of pro-angiogenic factors. In summary, the data presented in this thesis provide convincing evidence that FKBPL plays an important role in regulating body weight, glucose metabolism, endothelial function, angiogenesis, inflammation and cardiac function in both the non-diabetic and diabetic setting. Moreover, FKBPL is implicated in dysregulated angiogenesis associated with placental development in the presence of pre-eclampsia or diabetes during pregnancy. This suggests that FKBPL could be explored as a novel target for prevention and/or treatment of cardiovascular disease. Thesis embargoed until 31st December 2024