Ulm, Univ., Diss., 1999.

Tübingen, Univ., Diss., 2003.

Zugl.: Berlin, Freie Univ., Diss., 2008

Zugl.: Berlin, Freie Universiẗat, Diss., 2008.

As cartilage tissue has limited repair capacities, tissue engineering has emerged as a promising alternative for cartilage repair. The scaffold is a primary component of the tissue engineering design, yet little information exists regarding the effects of polymer and scaffold properties on tissue growth. In this study, we have developed a novel scaffold, PLG microspheres, for use in cartilage tissue engineering, which has the capacity for alterations in polymer and scaffold. We examined the effects of molecular weight, hydrophobic capping, delivery of Mg(OH)2, microsphere size, and controlled release of IGF-I. Our findings demonstrated that polymer parameters distinctively affect tissue and matrix output. Specifically, micro spheres with high molecular weight polymer produced tissue with high GAG content and tissue mass in vivo and in vitro, while micro spheres with capped polymer induced steady tissue and matrix accumulation, but may have precluded cell attachment. Release of buffer to the growing cartilage had negative effects on tissue formation in vivo and in vitro. Additionally, increasing microsphere diameter generated more samples with center of necrotic tissue. The presence of microspheres induced greater cartilage mass and matrix content than cartilage from cells alone. Delivery of IGF-I induced a dose-dependent effect on matrix and tissue production in vivo, with the highest effective load of IGF-I (0.3%) generating the most matrix and tissue accumulation. In contrast, the in vitro IGF-I dose-dependent effect induced on matrix and tissue production peaked at a dose of 0.02% IGF-I, with higher doses generating less tissue and matrix. Taken together, changes in polymer or scaffold composition and release of growth factor can be optimized to form cartilage with enhanced tissue parameters. Moreover, these results demonstrate a novel scaffold with potential to support cartilage regeneration and provide simultaneous drug delivery.

The potassium channels IK and IK1, responsible for the action potential repolarization and resting potential respectively, are altered during cardiac hypertrophy. The activation of insulin-like growth factor-I (IGF-I) during hypertrophy may affect channel activity. The aim was to examine the modulatory effects of IGF-I on IK and IK1 through mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways during hypertrophy. With the use of specific inhibitors for ERK1/2 (PD98059), p38 MAPK (SB203580) and PI3K/Akt (LY294002), Western blot and whole cell patch-clamp were conducted on sham and aorto-caval shunt-induced hypertrophy adult rat myocytes. Basal activation levels of MAPKs and Akt were increased during hypertrophy. Acute IGF-I (10-8 M) enhanced basal activation levels of these kinases in normal hearts but only those of Akt in hypertrophied ones. IK and IK1 activities were lowered by IGF-I. Inhibition of ERK1/2, p38 MAPK, or Akt reduced basal IK activity by 70, 32, or 50%, respectively, in normal cardiomyocytes vs. 53, 34, or 52% in hypertrophied ones. However, basal activity of IK1 was reduced by 45, 48, or 45% in the former vs. 63, 43, or 24% in the latter. The inhibition of either MAPKs or Akt alleviated IGF-I effects on IK and IK1. We conclude that basal IK and IK1 are positively maintained by steady-state Akt and ERK activities. K+ channels seem to be regulated in a dichotomic manner by acutely stimulated MAPKs and Akt. Eccentric cardiac hypertrophy may be associated with a change in the regulation of the steady-state basal activities of K+ channels towards MAPKs, while that of the acute IGF-I-stimulated ones toward Akt. .

No description available.

No description available.

No description available.

Development of the mammary gland is likely mediated by locally produced growth factors acting in concert with circulating mitogens. To investigate the importance of mammary synthesis of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBP), the initial objective was to evaluate the physiological effects of recombinant IGF-I synthesis in the mouse mammary gland. Expression of recombinant IGF-I was targeted by the mouse mammary tumor virus - long terminal repeat (MMTV-LTR) to the mammary glands of two lines (15 and 29) of transgenic mice. Mammary synthesis of recombinant IGF-I increased the frequency of appearance of mammary alveolar buds (71% vs. 21%) in transgenic compared with non-transgenic CD-1 mice. During lactation, mammary synthesis of recombinant IGF-I reduced the amount of endogenous native IGF-I secreted into milk of transgenic mice. Regardless of transgenesis, a shift in the milk IGFBP profile from predominantly IGFBP-3 to a lower molecular weight IGFBP occurred between d 8 and d 12 of lactation. The altered composition of milk from transgenic line 29 dams reduced by 27% the average daily gain of suckling litters, compared with CD-1 dams. Moreover, mammary glands of transgenic mice were less regressed after weaning than controls and were characterized by the presence of more organized secretory lobules. The second overall objective was to evaluate the regulation and physiological effects of mammary IGF-I and IGFBP synthesis in prepubertal heifers. Serum and extracts of mammary tissue at 5% concentration in media stimulated DNA synthesis 545% and 28%, respectively, in primary mammary epithelial organoids in collagen gel culture. Addition of IGFBP-3 strongly inhibited this growth response. High feeding level tended to increase IGFBP-3 levels in mammary tissue and reduced by 30% the growth response to mammary tissue extracts. Somatotropin increased the mitogenic response to mammary extracts at high feeding level and increased the tissue content of IGF-I by 46%. In summary, local synthesis of IGF-I and IGFBP is influenced by feeding level and exogenous somatotropin and contributes substantially to effects on mammary cell proliferation. Interactions of locally produced IGFBP-3 with IGF-I and other growth factors appear to be especially important when mammary growth is modulated by feeding level. / Ph. D.