Microvessel precursor smooth muscle cells express head-inserted smooth muscle myosin heavy chain (SM-B) isoform in hyperoxic

Abstract

The present study analyzes smooth muscle myosin heavy chain (SMMHC) expression as lung microvascular precursor smooth muscle cells (PSMCs), cells derived from fibroblasts and intermediate cells (immature SMCs), acquire a smooth muscle phenotype in an in vivo model of pulmonary hypertension (PH). Because of the unique contractile properties of the SMMHC isoform SM-B, we analyzed its expression in the microvessels (<100 micrometers diameter) and in larger vessels (100-700 micrometers) quantitatualy by the labeled [strept]avidin-biotin technique (day 1-28), and related this to cell phenotype by transmission microscopy and protein A-gold labeling (at day 28). Airway SMCs of the normal and hypertensive lung uniformly expressed SM-B whereas vascular SMC expression was heterogeneous. Thus, in some large arteries (and veins) SMCs contained cells expressing SM-B while in others all the cells were immunonegative. Microvascular cells expressing SM-B (arteries and veins) were rare in normal lung and numerous in PH, increasing as wall muscle developed in smaller segments with time. As in large vessels, some microvessels had immunopositive cells and others only negative ones. Ultrastructural analysis confirmed that the SMCs of bronchial vessels, and the septal SMCs adjoining alveolar ducts, contained dense filament arrays decorated with SM-B. While the PSMC processes of the normal lung contained sparse filaments decorated with SM-B, these cells expressed dense filament arrays in PH. Fibroblasts migrating to align around the microvessels also expressed SM-B but in the absence of a filament network. For the first time, we demonstrate in vivo that newly developed microvascular PSMCs express the SMMHC SM-B isoform in PH.

Pulmonary Hypertension after Prolonged Hypoxic Exposure in Mice with a Congenital Deficiency of Cyp2j

“…The noted shift to a-SMA expression by endothelial cells we report likely occurs in the absence of the development of a filament network characteristic of contractile cells (31,32). Prolonged exposure to decreased oxygen concentrations results in marked phenotypic changes in all of the cells that comprise the pulmonary artery (23).…”

“…This finding indicates that Cyp2j deficiency induced pulmonary vascular neomuscularization presumably by the distal migration of smooth muscle cells into alveolar cells (30). Alternatively, this ORIGINAL RESEARCH neomuscularization may result from the development of precursor SMCs surrounding the pulmonary vessels (31,32).…”

(+)Insert smooth muscle myosin heavy chain (SM-B) isoform expression in human tissues

“…This could explain why mRNA coding for the (ϩ)insert SMMHC was found in all human tissues tested except for the bone marrow. It was shown previously that the (ϩ)insert SMMHC is the dominant isoform in rat and rabbit small vessels and arterioles (6,15,45), and blood vessels could also explain the signal detected for this isoform in all human Fig. 7.…”

“…Briefly, 1 g of human bladder total RNA (BD Clontech), in a total reaction volume of 20 l, was reverse transcribed with oligo(dT) [12][13][14][15][16][17][18] primer, Superscript II, and RNAguard ribonuclease inhibitor (Amersham Pharmacia). Primers flanking the hypothetical region containing the code for the insert were designed from human (Ϫ)insert SMMHC (GenBank accession no.…”

Mosaic Tumor Vessels: Cellular Basis and Ultrastructure of Focal Regions Lacking Endothelial Cell Markers

“…One half of the tumor was then prepared for sequential confocal and electron microscopy analysis, and the other for immunohistochemical analysis of the basement membrane (see below). For the sequential confocal and electron microscopy study, the tissue was dehydrated and embedded in LR White without postfixation in osmium tetroxide (18).…”