[Mechanism of vitamin D deficiency involvement in the development of pulmonary arterial hypertension related to monocrotaline-induced connective tissue disease in rats].

<b>Objective:</b> To investigating the impact of vitamin D (VitD) deficiency on the jagged 1 protein (Jagged1)/Notch3 signaling pathway in the pulmonary arteries of rats with monocrotaline (MCT)-induced connective tissue disease (CTD)-related pulmonary arterial hypertension (PAH) and to explore the pathological and molecular mechanisms of VitD involvement in the development of CTD-PAH. <b>Methods:</b> Twenty-four 7-week-old male Wistar rats were divided into a normal diet group and a VitD-free diet group using random number table, with 12 rats in each group. After 5 weeks of feeding, the rats were further randomly divided into saline and MCT groups, forming group A (normal diet+saline), group B (normal diet+MCT), group C (VitD-free+saline), and group D (VitD-free+MCT), with 6 rats in each group, and the rats were continued to be fed for another 4 weeks. The MCT group was injected with MCT solution subcutaneously on the back of the neck to construct the CTD-PAH model, and the saline group was injected with an equal amount of saline as a control. At the end of the experiment, blood samples were collected from all rats, and the serum 1, 25-dihydroxy vitamin D levels were determined by enzyme-linked immunosorbent assay. Hemodynamic measurements were performed on all rats, recording and calculating the mean values of right ventricular pressure and pulmonary artery pressure. Lung tissues and pulmonary arteries of all rats were stained with hematoxylin-eosin staining, the inner and outer diameters of pulmonary vessels were measured, and the percentage of pulmonary artery medial layer thickness was calculated. The right ventricular hypertrophy index was determined by weighing the parts of the heart and calculating the ratio. The apoptosis of pulmonary artery smooth muscle cells was assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling. The expression levels of Jagged1, Notch3, and hairy and enhancer of split-1 (Hes1) mRNA and protein in the pulmonary arteries were analyzed by reverse transcription quantitative polymerase chain reaction and Western blotting. <b>Results:</b> The serum 1, 25-dihydroxy vitamin D levels in group D were significantly lower than those in groups A, B, and C [(51.01±0.96) μg/L, (65.15±1.83), (57.49±0.28), (54.52±2.87) μg/L, respectively, all <i>P</i><0.05]. The right ventricular pressure, pulmonary artery systolic pressure, pulmonary artery diastolic pressure, and mean pulmonary artery pressure in Group D rats were significantly higher than those in groups A, B and C (all <i>P</i><0.05). The percentage of pulmonary artery medial layer thickness in group D (56.28%±9.51%) was significantly higher than that in Groups A (21.28%±1.89%), B [22.72% (22.16%, 30.10%)], and C (38.73%±7.34%) (all <i>P</i><0.05); the right ventricular hypertrophy index in group D (45.74%±12.68%) was significantly higher than that in groups A (21.78%±2.80%), B (40.93%±9.10%), and C (23.71%±1.22%) (all <i>P</i><0.05). The apoptosis of pulmonary artery smooth muscle cells in group D (0.07±0.01) was significantly lower than that in groups A (1.00±0.08), B (0.17±0.02), and C (0.49±0.07) (all <i>P</i><0.05). The levels of Jagged1, Notch3, and Hes1 mRNA and protein in Group D were all significantly higher than those in Groups A, B, and C (all <i>P</i><0.05). <b>Conclusions:</b> VitD deficiency is involved in the pathophysiological mechanisms of CTD-PAH development. This occurs by upregulating the expression of the Jagged1/Notch3/Hes1 pathway in the pulmonary arteries of rats with MCT-induced PAH. The consequences include pulmonary artery thickening, increased pulmonary artery pressure, increased right ventricular pressure, right ventricular hypertrophy, and decreased apoptosis of pulmonary artery cells.