Platelet-derived growth factor and its role in atherogenesis: a brief review

Endobiogeny: a global approach to systems biology (part 2 of 2)

ENDOBIOGENY AND THE BIOLOGY OF FUNCTIONS ARE BASED ON FOUR SCIENTIFIC CONCEPTS THAT ARE KNOWN AND GENERALLY ACCEPTED: (1) human physiology is complex and multifactorial and exhibits the properties of a system; (2) the endocrine system manages metabolism, which is the basis of the continuity of life; (3) the metabolic activity managed by the endocrine system results in the output of biomarkers that reflect the functional achievement of specific aspects of metabolism; and (4) when biomarkers are related to each other in ratios, it contextualizes one type of function relative to another to which is it linked anatomically, sequentially, chronologically, biochemically, etc.

Simultaneous analysis of 1176 gene products in normal human aorta and abdominal aortic aneurysms using a membrane-based complementary DNA expression array

BACKGROUND

A number of changes in gene expression have been described in abdominal aortic aneurysms (AAAs), but the spectrum of molecular alterations in this disease is unknown. The purpose of this study was to characterize the expression of approximately 1000 gene products in human AAA tissue and to compare the profile of genes expressed in AAAs with that observed in normal aorta.

MATERIALS AND METHODS

Total RNA was isolated from abdominal aortic wall tissues (4 AAAs and 4 normal aortas), and array-specific [(32)P]-labeled complementary DNA (cDNA) probes were created with reverse transcription. The cDNA probes were hybridized with nylon membranes containing an array of 1176 cDNA clones (AtlasArray Human 1.2 I; Clontech, Palo Alto, Calif), and autoradiographs were scanned to identify the patterns of gene expression characteristic of each tissue type. Densitometric analysis was used to standardize the expression of individual genes to a panel of housekeeping controls, and differential gene expression was defined by a signal ratio of at least 2:1.

RESULTS

One hundred forty-five (12.3%) of the 1176 genes were consistently expressed in aortic tissue. Thymosin beta-4 was the most abundant of 101 transcripts detected in both AAAs and normal aorta, whereas 44 genes exhibited differential patterns of expression (39 predominant in AAAs and 5 in normal aorta). Densitometric analysis confirmed differences in expression for 20 of these gene products between AAAs and normal aorta, with the greatest increases seen for myeloid cell nuclear differentiation antigen (31-fold), cathepsin H (30-fold), platelet-derived growth factor-A (23-fold), apolipoprotein E (13-fold), gelatinase B/matrix metalloproteinase-9 (12-fold), and interleukin-8 (11-fold). The only gene products substantially decreased in AAAs were myosin light chain kinase (39-fold) and beta-1 integrin (twofold). AAA tissues thereby exhibited a distinct pattern of gene expression reflecting chronic inflammation, extracellular matrix degradation, atherosclerosis, and smooth muscle cell depletion.

CONCLUSIONS

cDNA expression arrays provide a powerful new approach to help identify the molecular mechanisms responsible for aneurysmal degeneration. Further studies will be needed to elucidate the functional and pathophysiologic significance of the individual genes that exhibit altered levels of expression in AAA tissue.

Growth factors and their implications for clinicians: a brief review

Growth factors play a vital role in both homeostasis and disease. In recent years considerable research has revealed the importance of growth factors in biology and they are now becoming incorporated in the clinical literature. Growth factors are peptides (protein fractions) that transmit signals within and between cells. They were discovered in the early 1960s as growth stimulants in tissue culture. It is now evident that growth factors play a comprehensive role in the modulation of tissue growth and development. The modes of action of growth factors are discussed with examples pertinent to clinical dentistry.

Effect of platelet-derived growth factor on tibial osteotomies in rabbits

The effect of exogenous platelet-derived growth factor (PDGF) BB on bone healing was tested in a pilot study using a unilateral tibial osteotomy in rabbits. Each osteotomy was injected with collagen or collagen containing 80 micrograms of PDGF. At 28 days, both tibiae from each rabbit were harvested and subjected to three-point bending to failure. The effect upon bone healing was tested by comparing the healing rates of PDGF-treated and -nontreated osteotomies with their respective normal contralateral bones. Three animals died before 28 days. The remaining 6 experimental and 5 control animals were available for assessment. Radiographically, at 2 weeks and 4 weeks, there was a clear increase in callus density and volume around the PDGF-treated osteotomies compared with the control rabbits' osteotomies. Osteotomies treated with PDGF were not statistically different in strength from their nonoperated contralateral bones. In the control group, however, the osteotomies were statistically weaker than their nonoperated (contralateral) bones. Microscopically, it was generally observed that PDGF-treated tibiae displayed a more florid and advanced state of osteogenic differentiation, both endosteally and periosteally, than the control osteotomies. Radiographic, mechanical, and histopathological data suggest that exogenous PDGF has a stimulatory effect on fracture healing.