Date of Award
Doctor of Philosophy in Pharmaceutical Sciences
Biomedical and Pharmaceutical Sciences
Preterm birth (PTB) is the major determinant of perinatal morbidity and mortality, and accounts for the second most common cause of neonatal death across the world. Approximately, one in every ten newborns is born prematurely (before 37 completed weeks of gestation) amounting to an estimated global 15 million premature births every year. Preterm neonates are vulnerable to a wide range of short and long term metabolic, infectious, neurological, and respiratory morbidities. PTB is characterized by different complex multifactorial process manifested by diverse pathogenetic mechanisms. Despite many efforts to understand the timing of parturition, the molecular mechanisms through which PTB is triggered are not fully understood.
Pregnant women with different hepatic dysfunctions like nonalcoholic fatty liver disease, acute fatty liver of pregnancy, intrahepatic cholestasis of pregnancy (ICP), hepatitis B virus, hepatitis C virus, jaundice, and drugs induced liver injuries are at increased risk of PTB. Amongst these liver disorders, ICP is the most common pregnancy-specific liver disease and typically develops in the late second trimester or early third trimester of pregnancy. In manuscript 1, the purpose of the study was to investigate whether dysregulation of bile acid (BA) increases the risk for PTB, and to identify whether it is the liver injury itself or the elevated serum BA which directly induces PTB. Bile acids (BAs) are considered as signaling molecules involved in the regulation of various metabolic and cellular activities. Dysregulation of BAs has been identified as a causative factor for the induction of various diseases. But so far it has not been directly linked to the etiology of PTB. In this study, we successfully induced PTB in mice with liver injuries and dysregulated BAs. In addition, BA administration induced PTB in mice without causing liver toxicities, and serum BA levels directly correlated with the rates of PTB. Of importance, we also identified that it was the elevated BA not the liver injury by itself that induced PTB. Furthermore, the rates of PTB and survival of newborns were markedly improved by restoring BA homeostasis through farnesoid X receptor (FXR) activation. The findings thus establish a direct etiological link between BA and PTB in pregnant subjects with liver dysfunctions and holds a great promise to develop therapies to either prevent or delay PTB in pregnant women vulnerable to PTB.
In manuscript 2, we present a novel potential mechanism by which BA induce PTB through Takeda G-protein receptor-5 (TGR5) regulated C5a/C5aR1 signaling pathway. Although, the association between elevated maternal serum total bile acid (sTBA) and PTB has been previously established, but the underlying mechanism how BA trigger PTB is lacking. The best characterized receptors amongst the bile acid activated receptor (BAR) are FXR and TGR5. Although FXR (-/-) mice gave birth in the normal range of gestation, the G.Ds were significantly reduced compared to WT mice, a PTB-like phenotype. Such PTB-like phenotype is consistent with elevated sTBA levels in FXR (-/-) mice. The results thus indicate that it is unlikely that BA induce PTB through FXR. On the other hand, TGR5 antagonist SBI-115 induced PTB, indicating that BA induces PTB via TGR5. Moreover, incubation of human and mouse myometrium with C5a has been demonstrated previously, that C5a is a uterotonic agent. In addition, C5aR1(-/-) mice were protected against LPS-induced miscarriage. However, the role of C5a/C5aR1 signaling pathway in BA induced PTB is unknown. In this study, we investigated the effect of cholic acid (CA) on TGR5 and C5aR1 expression in vivo in mice and in vitro in myometrial and endometrial cells. We found that CA had minimal effects on the overall expression of TGR5 both in vivo and in vitro. On the other hand, CA significantly increased the mRNA and protein expression levels of C5aR1 both in vivo and in vitro. Similarly, the serum and amniotic fluid (A.F) concentrations of C5a, and serum concentration of IL-6 were markedly increased in CA treated mice. In addition, CA and SBI-115 treatments increased the mRNA and proteins expressions of C5aR1 and cAMP concentrations in vitro. On the contrary, treatment with TGR5 agonist CCDC in vitro decreased the mRNA and proteins expressions of C5aR1 and cAMP concentrations. Taken together, it was concluded that elevated BA concentration induced PTB via TGR5 regulated C5a/C5aR1 signaling pathway which in response induced inflammatory responses via IL-6. Modulating C5a/C5aR1 signaling pathway may represent a new approach to develop therapies to prevent or delay PTB in pregnant women with liver disorders.
Hashmi, Syed Fayaz Ul Haq, "THE MECHANISTIC AND ETIOLOGICAL LINK BETWEEN BILE ACID DYSREGULATION AND PRETERM BIRTH" (2022). Open Access Dissertations. Paper 1449.