Developmental expression of latent transforming growth factor beta binding protein 2 and its requirement early in mouse development.

Latent transforming growth factor beta (TGF-beta) binding protein 2 (LTBP-2) is an integral component of elastin-containing microfibrils. We studied the expression of LTBP-2 in the developing mouse and rat by in situ hybridization, using tropoelastin expression as a marker of tissues participating in elastic fiber formation. LTBP-2 colocalized with tropoelastin within the perichondrium, lung, dermis, large arterial vessels, epicardium, pericardium, and heart valves at various stages of rodent embryonic development. Both LTBP-2 and tropoelastin expression were seen throughout the lung parenchyma and within the cortex of the spleen in the young adult mouse. In the testes, LTBP-2 expression was seen within lumenal cells of the epididymis in the absence of tropoelastin. Collectively, these results imply that LTBP-2 plays a structural role within elastic fibers in most cases. To investigate its importance in development, mice with a targeted disruption of the Ltbp2 gene were generated. Ltbp2(-/-) mice die between embryonic day 3.5 (E3.5) and E6.5. LTBP-2 expression was not detected by in situ hybridization in E6.5 embryos but was detected in E3.5 blastocysts by reverse transcription-PCR. These results are not consistent with the phenotypes of TGF-beta knockout mice or mice with knockouts of other elastic fiber proteins, implying that LTBP-2 performs a yet undiscovered function in early development, perhaps in implantation.

Alterations in cyclic AMP metabolism in human bronchial asthma. II. Leukocyte and lymphocyte responses to prostaglandins.

In an effort to clarify the basis for the reduced cyclic AMP response to catecholamines in leukocytes and lymphocytes from asthmatic donors the response of these cells to prostaglandins has been examined. Cells with an impaired beta adrenergic response had an essentially unaltered response to prostaglandin E(1) (PGE(1)) indicating the presence of selective beta adrenergic blockade. In contrast to what was observed with cells from asthmatic individuals, in normal control leukocytes with reduced catecholamine responsiveness PGE(1) responses were usually reduced as well, suggesting a different mechanism. The excellent cyclic AMP response to PGE(1) in cells from asthmatic donors would suggest that the defect in catecholamine responsiveness is at the level of the beta adrenergic receptor although a contributory role of altered substrate concentrations or increased phosphodiesterase activity is not formally excluded.

Alterations in cyclic AMP metabolism in human bronchial asthma. 3. Leukocyte and lymphocyte responses to steroids.

On the basis of serial studies the responsiveness of leukocytes and lymphocytes from asthmatic donors to catecholamines was increased during high dose corticosteroid therapy. Similar changes were observed in the cells of normal control subjects given 200 mg of hydrocortisone intravenously. The increase in responsiveness did not appear to be due to changes in lymphocyte subpopulations although this may be a contributing factor. In an effort to elucidate the basis for the improved response, in vitro effects of glucocorticoids on lymphocyte cyclic AMP concentrations were investigated. Glucocorticoids (prednisolone succinate, hydrocortisone, hydrocortisone phosphate, and hydrocortisone succinate) stimulated cyclic AMP accumulation in asthma and normal control lymphocytes, increases occurring within the first 2 min of incubation. In the absence of theophylline, responses were regularly obtained at 10 muM hydrocortisone and usually at 1 muM hydrocortisone but not at submicromolar steroid concentrations. Theophylline potentiated the cyclic AMP response to glucocorticoids and also increased the percentage of positive responses in the 0.01-1.0 muM corticosteroid range. Combinations of 1 muM hydrocortisone and 1 muM epinephrine were sometimes additive or synergistic but in many instances higher glucocorticoid concentrations were needed to obtain augmentation of the catecholamine response. The in vitro glucocorticoid effects may not fully explain their potentiating action in vivo.