Circulating Levels of Thrombospondin and Cellular Adhesion Molecules during Haemodialysis in Patients with Chronic Renal Impairment

Abstract

Heart development depends on a finely balanced interplay of cardiomyocyte proliferation and differentiation. Understanding the molecular basis of these events will be crucial to the development of therapies that repair damaged hearts. By means of a transgenic mouse model, we demonstrate that Hop, an atypical 73 amino-acid homeodomain protein expressed in the developing heart, has a vital role regulating growth and development of cardiac cells. Pronuclear microinjection of FLAG-tagged mHop cDNA (driven by a CMV enhancerhat MLC-2v promoter complex that is active only in the developing heart, with peak activity around E12.5) produced 2 independent founder lines of the CBAUC57BL6 background. Southern blotting and real-time PCR confirmed transgene integration into the genome, with approximately 8 transgene copies in each line. Myocardium-specific FLAG-mHop protein expression was demonstrated by Western blot analysis of E12.5 transgenic hearts. Viable and fertile transgenic offspring were generated from both founders. There was a consistent stage-dependent cardiac phenotype: prior to E12.5, a small proportion of transgenic hearts were abnormally elongated along their longitudinal axes, due to eccentric cardiac hyperplasia, particularly at the ventricular apex. After E12.5, -10% of transgenic mouse hearts showed arrested development: these hearts, while normal in shape, were dilated and had extremely thin and hypocellular ventricular walls. Thereafter, as transgene expression waned, apparent compensation allowed the hearts to recover a normal morphology at E18.5. Interpretation of transgenic microarray gene expression data is ongoing. Echocardiography and invasive haemodynamic studies in adult mice will establish if there are long-term cardiac sequelae in the transgenic population. The incomplete penetrance and stage-specific cardiac dimorphism in our transgenic mice complements recently published Hop' knockout models (Cell 2002, 110, 713-735). a minority of which additionally developed heart failure in adulthood. Consistent with these reports, we propose that HOP initially expands the myocardium during early heart development, limiting cardiac cell proliferation later on.