MYOSIN HEAVY-CHAIN ISOFORM COMPOSITION AND DISTRIBUTION IN DEVELOPINGAND ADULT HUMAN AORTIC SMOOTH-MUSCLE

The myosin heavy-chain (MHC) composition of developing and adult human aortic smooth muscle (SM) was studied by SDS-polyacrylamide gel elect ro-phoresis, Western blotting and indirect immunofluorescence using a panel of anti-MHC antibodies. On 5% SDS gels, three bands of 204, 200 and 196 kDa apparent molecular mass were identified in fetal, infant a nd adult stages of development. In the extracts from thoracic aorta (u pper level), the 204, and 200-kDa bands (designated as SM-1 and SM-2, respectively) were recognized by SM-G4 and SMMS-1 antibodies, raised a gainst a SM antigen, whereas the 196-kDa band was reactive with nonmus cle (NM)-F6 and NM-G2 antiplatelet MHC antibodies. Western blotting an d immunofluorescence tests performed on bovine brain and other human N M tissues using NM-F6 and NM-G2 indicated that antigenic targets of th e two antibodies resembled that of so-called IIB and IIA NM myosin fou nd in the bovine system, respectively. In the aortic media, SM-1 was e xpressed throughout development, while SM-2 was upregulated during lat e fetal and postnatal development. Similarly, the 196-kDa band showed two distinct patterns of immunoreactivity with the anti-NM-MHC antibod ies: with NM-G2, antigenicity was equal at all the developmental stage s examined, whereas with NM-F6, it diminished during postnatal develop ment. In the upper level, the cellular distribution of NM-G2 and NM-F6 immunoreactivities was similar in the early fetus but quite distinct at later stages of development. In infant and adult subjects, SM cells (SMC) reactive with NM-F6 accumulated predominantly within the intima l layer as well as in some areas of the underlying media as cell foci, whereas NM-G2 homogeneously stained the two layers. In the aorta near the diaphragm (lower level), both antibodies stained the thickened in tima but not the underlying media. These data are consistent with the existence of developmental, stage-specific molecular and cellular tran sitions during vascular SMC maturation in human aortic media. In addit ion, these data suggest that IIB-like myosin may be expressed in SMC i nvolved specifically in intimal thickening.