Rationale:The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels.Objective: We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV (Col15a1 ؊/؊ ) to define its functional role in the vasculature and in age-and hypertension-associated myocardial remodeling. Methods and Results:Cardiac structure and vasculature were analyzed by light and electron microscopy.Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 ؊/؊ mice. Key Words: cardiomyopathy Ⅲ collagen Ⅲ extracellular matrix Ⅲ hypertension Ⅲ microcirculation T he extracellular matrix (ECM) has an important role in cardiac remodeling, defined by the adaptive changes in left ventricular structure, geometry, and function that follow cardiovascular stress in hypertensive heart disease, cardiomyopathies, or myocardial infarction and also as a function of age. 1 Degradation of myocardial collagens results in decreased ventricular stiffness and dilatation, whereas an increase in the total interstitial collagen content and crosslinking results in a stiffer myocardium and ventricular diastolic dysfunction. 2 Cardiomyopathy may result from a variety of acquired or genetic factors. In the absence of coronary artery disease, a significant proportion of cardiomyopathies are attributable to a genetic cause, eg, hereditary forms are present in approximately 30% to 50% of patients experiencing dilative cardiomyopathy (DCM), and mutations in more than 30 genes have been linked to this disease. 3 Many defects in cytoskeletal and sarcomeric proteins involved in cardiomyocyte contraction and force production have been associated with familial DCM, but most of the genetic defects and pathophysiological mechanisms have still not been identified. 4 Recent studies using genetically modified mice suggest that altered cell-ECM interactions and cell-cell adhesion via the intercalated discs may be involved in DCM pathogenesis. [5][6]...

Although the Schwann cell basement membrane (BM) is required for normal Schwann cell terminal differentiation, the role of BMassociated collagens in peripheral nerve maturation is poorly understood. Collagen XV is a BM zone component strongly expressed in peripheral nerves, and we show that its absence in mice leads to loosely packed axons in C-fibers and polyaxonal myelination. The simultaneous lack of collagen XV and another peripheral nerve component affecting myelination, laminin ␣4, leads to severely impaired radial sorting and myelination, and the maturation of the nerve is permanently compromised, contrasting with the slow repair observed in Lama4 Ϫ/Ϫ single knock-out mice. Moreover, the Col15a1 Ϫ/Ϫ ;Lama4 Ϫ/Ϫ double knock-out (DKO) mice initially lack C-fibers and, even over 1 year of age have only a few, abnormal C-fibers. The Lama4 Ϫ/Ϫ knock-out results in motor and tactile sensory impairment, which is exacerbated by a simultaneous Col15a1 Ϫ/Ϫ knock-out, whereas sensitivity to heat-induced pain is increased in the DKO mice. Lack of collagen XV results in slower sensory nerve conduction, whereas the Lama4 Ϫ/Ϫ and DKO mice exhibit increased sensory nerve action potentials and decreased compound muscle action potentials; x-ray diffraction revealed less mature myelin in the sciatic nerves of the latter than in controls. Ultrastructural analyses revealed changes in the Schwann cell BM in all three mutants, ranging from severe (DKO) to nearly normal (Col15a1 Ϫ/Ϫ ). Collagen XV thus contributes to peripheral nerve maturation and C-fiber formation, and its simultaneous deletion from neural BM zones with laminin ␣4 leads to a DKO phenotype distinct from those of both single knock-outs.