Impaired miR449a-induced downregulation of Crhr1 expression in low-birth-weight rats.

Low birth weight (LBW) is related to increased incidence of common cardiovascular and metabolic disorders, and psychopathologies later in life. Recent studies have suggested that maternal malnutrition affects fetal hypothalamic-pituitary-adrenal (HPA) axis programing although the mechanism is unknown. We demonstrated that LBW offspring delivered from malnourished dams showed prolonged elevated plasma corticosterone concentrations when compared with those of normal-birth-weight (NBW) offspring and impaired downregulation of corticotropin-releasing factor receptor type 1 (CRF-R1, Crhr1) in the anterior pituitary in restraint. Restraint increased expression of miR449a, which we had previously demonstrated to be involved in Crhr1 downregulation, in the anterior pituitary and serum exosomal miR449a contents through glucocorticoids in NBW offspring, but not in LBW offspring. Although plasma corticosterone concentrations were higher at 2000 h than at 0800 h in both LBW and NBW offspring, they were significantly higher in LBW offspring than in NBW offspring at 2000 and 0200 h. There were no significant diurnal changes in miR449a expression levels in the anterior pituitary of either NBW or LBW offspring, but the expression was significantly lower in LBW offspring than in NBW offspring at 1400, 2000, and 0200 h. The expression levels of GAS5, which inhibits glucocorticoid receptor (GR) binding to glucocorticoid-responsive element, in the anterior pituitary of LBW offspring were elevated when compared with those of NBW offspring. The downregulation of GR found in NBW offspring did not occur in restrained LBW offspring. These results indicate that impaired miR449a expression, probably induced by increased GAS5 expression, causes dysregulation of Crhr1 expression in the anterior pituitary, resulting in prolonged HPA axis activation in restrained LBW offspring.