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Birth associated changes in pulmonary arterial connective tissue gene expression in the normal and hypertensive lung
R M Kitley1, A A Hislop, S M Hall
1Vascular Biology and Pharmacology Unit, Institute of Child Health, 30 Guilford Street, London, UK.
Insights
Connective tissue gene expression in porcine pulmonary arteries changes rapidly after birth, with distinct patterns for procollagen and tropoelastin. Hypoxia-induced pulmonary hypertension alters these developmental changes.
Area of Science:
- Developmental Biology
- Cardiovascular Research
- Molecular Biology
Background:
- Pulmonary arteries undergo significant structural and molecular remodeling after birth.
- Connective tissue proteins, such as procollagen and tropoelastin, are crucial for vascular development and function.
- Hypoxia-induced pulmonary hypertension can disrupt normal vascular development.
Purpose of the Study:
- To investigate the temporal and spatial expression of procollagen and tropoelastin mRNA in porcine pulmonary arteries from birth.
- To compare gene expression patterns in normal pulmonary arteries versus those with experimentally induced pulmonary hypertension.
Main Methods:
- In situ hybridization was used to study procollagen alpha1(I), procollagen alpha1(III), and tropoelastin mRNA expression.
- Immunohistochemistry was employed to detect Type III pN-procollagen, tropoelastin, collagen I, and collagen III.
- Studies were conducted on intrapulmonary arteries from normal piglets and piglets exposed to hypobaric hypoxia at various ages.
Main Results:
- Procollagen mRNA expression surged rapidly in the media and adventitia within the first 3 days post-birth, then declined.
- Tropoelastin mRNA expression was high at birth, decreasing after 6 days, with later shifts between media and adventitia.
- Hypoxia from birth prevented the normal increase in procollagen mRNA; hypoxia from 3 or 14 days had minimal impact on gene expression.
Conclusions:
- Pulmonary arteries exhibit rapid, temporally regulated changes in connective tissue gene expression during postnatal remodeling.
- Each connective tissue gene (procollagen, tropoelastin) follows a unique expression timeline.
- Hypoxia-induced pulmonary hypertension differentially affects the expression patterns of these connective tissue genes.
Objectives:
To determine the temporal and spatial expression of the connective tissue precursors, procollagen and tropoelastin mRNA in normal and pulmonary hypertensive porcine pulmonary arteries from birth onwards.
Methods:
Using in situ hybridisation, connective tissue gene expression for procollagen alpha1(I) and alpha1(III) and tropoelastin was studied in intrapulmonary arteries from normal piglets, 5 min-16 weeks, and from piglets made pulmonary hypertensive by exposure to hypobaric hypoxia for 3 days, from birth, 3 or 14 days of age. In addition, Type III pN-procollagen, tropoelastin and collagen I and III were studied by immunohistochemistry. Quantitative or semi-quantitative techniques were applied to both in situ and immunohistochemical studies.
Results:
Procollagen alpha1(I) and alpha1(III) mRNA expression increased rapidly in the media and adventitia between birth and 3 days of age (P<0.05). The increase was transient and the number of cells expressing procollagen mRNA decreased to the low newborn number after 6 days of age. Type III pN-procollagen immunostaining was greatest in newborn elastic and muscular arteries and then decreased. Collagen I and III increased mainly after 6 days of age. In animals exposed to chronic hypobaric hypoxia from birth, the increase in procollagens I and III mRNA was prevented. Exposure to hypoxia from 3 or 14 days led to little change in either gene expression or in procollagen and mature collagen from the normal. Tropoelastin gene expression was high at birth in the endothelium and media for the first 6 days, and then decreased. Normally, tropoelastin decreased in the media and increased in the adventitia after 16 days of age. Hypoxia had no effect on the mRNA but led to increased tropoelastin.
Conclusion:
We demonstrated marked, rapid changes in temporal and cell specific connective tissue gene expression in normal pulmonary arteries immediately after birth as the vasculature remodels. Each gene appeared to have its own timetable of expression and responded differently to hypoxia-induced hypertension.