Cell-cell matrix interactions in induced lung injury: III. Long term effects of X-irradiation on basal laminar proteoglycans

Accumulation of Glycosaminoglycans in Radiation-induced Muscular Fibrosis

The content and biosynthesis of glycosaminoglycans (GAGs) were studied in the pig thigh muscle after acute local gamma-irradiation. Seven months following irradiation, the muscular tissue next to the irradiation cone was replaced by severe mutilating fibrosis delimited by an intermediary perifbrotic zone. Fibrosis, perifibrotic tissue and normal muscle, were sampled and incubated with [3H]glucosamine and [35S]sulphate, and GAGs were isolated following pronase digestion. Results showed a parallel increase of collagen and GAG content in perifibrotic and fibrotic tissues. Sulphated GAGs, heparan sulphate and dermatan sulphate were preferentially accumulated in fibrotic tissue, while the hyaluronic acid content increased only slightly. Synthesis of sulphated GAGs was more elevated in fibrotic tissue than in perifibrotic zone as compared with normal muscle. Seven months after irradiation well-developed fibrotic tissue continued to synthesize and to accumulate extracellular matrix macromolecules, indicating the invasive aspect of post-irradiation fibrosis.

Microvascular and tumor cell alterations during continuous hyperfractionated irradiation: an electron microscopic investigation on the rat R1H rhabdomyosarcoma

PURPOSE

Conventionally fractionated y-irradiation results in severe damage of tumor capillaries associated with decreasing oxygen partial pressure within the tumor. The present study was undertaken to assess whether vasculo-connective changes are less pronounced after continuous hyperfractionated irradiation, implying better tumor oxygenation and improved radiosensitivity.

MATERIALS AND METHODS

Twenty rats with an isotransplanted R1H rhabdomyosarcoma were irradiated for 12 days with 2 daily fractions of 2.5 Gy (delta t = 6 h). After 0, 15, 30, 45, and 60 Gy, tumor tissue of 4 rats each was analyzed histologically and electron-microscopically.

RESULTS

Untreated rhabdomyosarcomas were composed of spindle-shaped tumor cells with numerous mitoses. There were many apoptotic nuclei and a large central necrosis. Tumor capillaries showed a continuous lining of flattened endothelial cells with broad overlapping cell contacts overlying a delicate continuous basal lamina. During irradiation, mean tumor volume declined from 1.9 cm3 to 1.2 cm3. The number of atypical mitoses and apoptoses increased and numerous giant tumor cells appeared. The proportion occupied by necrotic tumor tissue rose from 30% to 60%. After 15 Gy (3 days), a marked vasodilatation was apparent accompanied by an interstitial edema. Occasionally, endothelial cells were rounded up and showed indented nuclei, with the underlying basal lamina disintegrated. These changes progressed with increasing radiation doses. After 30 Gy (6 days), leukocytes started to adhere to the endothelial wall. Electron-dense fine fibrillar and basal lamina-like deposits appeared in the perivascular space. Endothelial cell edema was only observed after 60 Gy (12 days). Cell contact areas were shortened, however, the endothelial lining was not interrupted. No signs of radiation fibrosis were observed.

CONCLUSION

Continuous hyperfractionated irradiation induces relatively discrete alterations of the vasculo-connective tumor tissue as compared to conventional irradiation. This may be an advantage with respect to tumor blood flow, oxygenation, and thus, radiosensitivity.

Brain fibronectin expression in prenatally irradiated mice

Activation of gene transcription by radiation has been recently demonstrated in vitro. However, little is known on the specificity of these alterations on gene transcription. Prenatal irradiation is a known teratogen that affects the developing mammalian central nervous system (CNS). Altered neuronal migration has been suggested as a mechanism for abnormal development of prenatally irradiated brains. Fibronectin (FN), an extracellular glycoprotein, is essential for neural crest cell migration and neural cell growth. In addition, elevated levels of FN have been found in the extracellular matrix of irradiated lung. To test whether brain FN is affected by radiation, either FN level in insoluble matrix fraction or expression of FN mRNA was examined pre- and postnatally after irradiation. Mice (CD1), at 13 d of gestation (DG), served either as controls or were irradiated with gamma rays at 0.5 or 1 Gy. Control and irradiated animals were killed either at 13 DG, 14 DG, 17 DG, or 5, 6, or 14 d postnatal. Brain and liver were collected from offspring and analyzed for either total FN protein levels or relative mRNAs for FN and tubulin. Results of prenatal irradiation on reduction of postnatal brain weight relative to whole body weight and morphological reduction in cerebral cortex regions of postnatal brains are comparable to that reported by others. Insoluble matrix fraction (IMF) per gram of brain, liver, lung, and heart weight was not significantly different either between control and irradiated groups or between postnatal stages, suggesting that radiation did not affect the IMF. However, total amounts of FN in brain IMF at 17 DG were significantly different (p < .02) between normal (1.66 +/- 0.80 micrograms) and irradiated brains (0.58 +/- 0.22 microgram). FN mRNA was detectable at 13, 14, and 17 DG, but was not detectable at 6 and 14 d postnatal, indicating that FN mRNA is developmentally regulated. After 0.5 Gy of irradiation, expression of FN mRNA was reduced to 36% +/- 22% (1 h), 52% +/- 10% (1 d), and 76% +/- 10% (4 d) of the control level. After 1 Gy of irradiation, relative FN mRNA was 62% +/- 28% (1 h) and 75% +/- 3% (4 days) to the control level, respectively. This reduction was comparable to that reported by others for the cytoskeletal protein beta-actin. In contrast, mRNA for tubulin, another cytoskeletal protein, increased at 1 h after irradiation but then approached normal postnatally. The longer lasting alteration of FN may be more directly related to neural development, particularly if the reduction in FN is nonuniform.

Modification of anionic sites in myocardial capillary basal laminae of diabetic rats

Capillary basal laminar thickening is a distinctive feature of diabetic microangiopathy; however, the mechanism responsible for this abnormality remains to be clarified. Recent reports have described a reduction in the distribution of anionic sites in diabetic glomerular basement membranes, with the suggestion that this reduction may generate a compensatory synthesis of basal laminar constituents, causing laminar thickening. In order to provide additional information, the character and distribution of the basal laminar anionic profile were examined in the myocardium of diabetic rats. Diabetes mellitus was induced in 14 rats by injection with streptozotocin, ip; 6 rats served as controls. Myocardial tissue was subjected to Charonis' procedure for the demonstration of anionic sites with the cationic electron-dense dye, ruthenium red, following the sacrifice of the animals at intervals up to 11 months after the induction of the diabetes. The tissues were then processed routinely for electron microscopic examination. A total of 20 electron micrographs, at magnifications of 13,000x and 33,000x, were obtained from each rat for the quantitation of anionic sites. A length measuring 6 micron along each basal lamina was utilized for determining the number of anionic loci. Results of this study show that (1) the number and size of anionic sites in myocardial basal laminae is reduced in diabetic rats, (2) this decrease becomes more pronounced with prolongation of the diabetes, (3) it is detectable prior to the demonstration of basal laminar thickening by electron microscopy, and (4) enzyme digestion treatments indicated that heparan sulfate proteoglycan is the essential stainable component of the anionic sites. These findings provide evidence that the laminar anionic profile is altered in the diabetic myocardium and support the view that this abnormality constitutes a significant initial event in the pathogenesis of basal laminar thickening.

The ultrastructure of epithelial cells of the distal lung

This review has focused on the structural and functional characteristics of those epithelial cells that line the walls of the lower respiratory bronchioles, alveolar ducts, and alveoli. In all, five cells types were considered: Clara cells, types I, II, and III pneumocytes, and alveolar macrophages. In addition, a very brief mention of the structure and influence of the basement membrane in alveolar development and repair was included, as well as a brief review of the role of epithelial cells in response to selected deleterious influences. No attempt was made to extend this review to cover the structure and functions of the epithelial lining of the conducting portions of the respiratory system, or the exciting and expanding complexities and interrelationships of the septal stroma. Since the volume of literature encircling this subject has virtually exploded during the last 15 years, it becomes almost impossible to review all reports. However, attempts were made to be selective in citations. Insofar as future developments are concerned, much remains to be understood concerning (1) the responses of all cell types to cytotoxic influences, including their respective abilities to repair induced damage, (2) cell-cell and cell-extracellular matrix relationships in response to injury, (3) the uniqueness of the basement membrane in the lung in controlling permeability and gaseous exchange, (4) the role(s) of alveolar macrophages in response to injury and their relationships to the septal macrophage population, (5) the aberrations in the respective cell types that can give rise to neoplastic growth, and (6) the role of the immune system in responding to the general defense of the lung. Indeed much has been learned in the past 2 decades, and it is expected that a review of this sort 1 or 2 decades hence will elucidate many of the functions and structural modifications of the lung.