Phenotype and Physiological Significance of the Endocardial Smooth Muscle Cells in XXXX Failing Hearts.

@entity1 @entity712 @entity2283 @entity384 @entity2277 @entity299
BACKGROUND: -Extravascular smooth muscle cells are often observed in the endocardium of @entity1 failing hearts. Here we characterized the phenotype of those cells and investigated their physiological significance. METHODS AND RESULTS: -We examined left ventricular biopsy specimens obtained from 44 @entity1 with @entity384 and 6 nonfailing hearts. In Masson's trichrome-stained histological preparations, bundles of smooth muscle cells were seen localized in the endocardium in 23 of the 44 specimens (none of the 6 controls). These cells were immunopositive for a-smooth muscle actin, type 2 smooth muscle myosin, @entity2283 and calponin, but were negative for embryonic smooth muscle myosin, @entity2277 , fibronectin and periostin. This profile is indicative of a late differentiation (contractile) smooth muscle phenotype. Electron microscopy confirmed that phenotype, revealing the cells to contain abundant myofilaments with dense bodies but little rough endoplasmic reticulum or Golgi apparatus. In the endocardial smooth muscle-positive group, the left ventricular end-systolic volume index (73  34 vs. 105  50 mL/m(2), p = 0.021), left ventricular peak wall stress (164  47 vs. 196  43 dynes   10(3)/cm(2), p = 0.023) and left ventricular end-systolic meridional wall stress (97  38 vs. 121  37 dynes   10(3)/cm(2), p = 0.036) were all significantly smaller and the ejection fraction was larger (41  8.8 vs. 33  9.3%, p = 0.005) than in the endocardial smooth muscle-negative group. However, no histological parameters differed between the two groups. CONCLUSIONS: -Endocardial smooth muscle cell bundles in hearts with @entity384 exhibit a mature contractile phenotype and may play a compensatory role mitigating @entity712 by reducing left ventricular wall stress and @entity299 .
