Local Production Of Growth Factors Research Articles

The biology of integration of the anterior cruciate ligament

The anterior cruciate ligament (ACL) is a short, stout, intra-articular, extrasynovial structure which acts to control rotational movements and anterior translation of the femur upon the fixed tibia.[1][1] Rupture is a traumatic event, often as a consequence of twisting upon the weight-bearing limb

Initial upregulation of growth factors and inflammatory mediators during nerve regeneration in the presence of cell adhesive peptide‐incorporated collagen tubes

Neurotrophic factors play an important modulatory role in axonal sprouting during nerve regeneration involving the proliferation of hematogenous and Schwann cells in damaged tissue. We have exposed lesioned sciatic nerves to a collagen prosthesis with covalently bonded small cell adhesive peptides Arg-Gly-Asp-Ser (RGDS), Lys-Arg-Asp-Ser (KRDS), and Gly-His-Lys (GHK) to study local production of growth factors and cytokines in the regenerating tissues. Western/enzyme-linked immunosorbent assay (ELISA) studies were performed after 10 days of regeneration, when the tubular prosthesis is filled with fibrous matrix infiltrated by hematogenous cells and proliferating Schwann cells with growth factors produced locally. Regeneration was also analyzed by morphometrical methods after 30 days. The quantification of growth factors and proteins by ELISA revealed that there was an enhanced expression of the neurotrophic factors nerve growth factor (NGF) and neurotrophins (NT-3 and NT-4) in the regenerating tissues. This was further established by Western blot to qualitatively analyze the presence of the antigens in the regenerating tissues. Schwann cells were localized in the regenerating tissues using antibodies against S-100 protein. Other growth factors including growth-associated protein 43 (GAP-43), apolipoprotein E (Apo E), and pro-inflammatory cytokine like interleukin-1alpha (IL-1alpha) expression in the peptide groups were evaluated by ELISA and confirmed by Western blotting. Cell adhesive integrins in the proliferating cells were localized using integrin-alpha V. The combined results suggest that the early phase of regeneration of peripheral nerves in the presence of peptide-incorporated collagen tubes results in the enhanced production of trophic factors by the recruited hematogenous cells and Schwann cells, which in turn help in the secretion of certain vital trophic and tropic factors essential for early regeneration. Furthermore, hematogenous cells recruited within the first 10 days of regeneration help in the production of inflammatory mediators like interleukins that in turn stimulate Schwann cells to produce NGF for axonal growth.

Hypoxic Growth of Bovine Pulmonary Artery Smooth Muscle Cells: Dependence on Synergy, Heterogeneity, and Injury-Induced Phenotypic Change

Pulmonary artery (PA) smooth muscle cell (SMC) proliferation in response to hypoxia is a key component of the vascular remodeling that occurs in chronic hypoxic pulmonary hypertension.1,2,3 The traditional view has been that this hypoxic growth of PA SMCs is a direct consequence of sustained vasoconstriction and resulting mechanical stress, endothelial injury, and local growth factor production. Although hypoxia generally is not thought to directly promote proliferation of PA SMCs, we have discovered a novel proliferative synergism by which hypoxia could directly augment and sustain proliferative signals in the vessel wall.

Ovarian follicular dominance: the role of intraovarian growth factors and novel proteins.

Folliculogenesis is associated with the development of a group of follicles at various stages of maturation from which a species-specific number of follicles are selected for continued growth. These selected follicles, after being exposed to the requisite hormonal environment, ovulate in response to the preovulatory gonadotrophin surge. Follicular dominance is the mechanism by which the selected follicle(s) undergoes rapid development in an environment where growth and development of other follicles, recruited at a similar time, are suppressed. These processes are controlled by the interaction of endocrine signals and locally produced ovarian growth factors. The response of the two major follicular cell types, granulosa and theca cells, to gonadotrophins is regulated by the local production of growth factors. Mechanisms controlling growth factor action occupy a central role in the regulation of folliculogenesis. In this review, we highlight the influence of the extracellular matrix in this process by describing its involvement in regulating the activity of components of the insulin-like growth factor system, transforming growth factor beta superfamily, fibroblast growth factors and the epidermal growth factor/transforming growth factor alpha family. In addition, some recent studies on the role of protein factors produced by the dominant follicle in maintaining dominance and inhibiting the growth of subordinate follicles are described.

Surface roughness modulates the local production of growth factors and cytokines by osteoblast-like MG-63 cells

Titanium (Ti) surface roughness affects proliferation, differentiation, and matrix production of MG-63 osteoblast-like cells. Cytokines and growth factors produced in the milieu surrounding an implant may also be influenced by its surface, thereby modulating the healing process. This study examined the effect of surface roughness on the production of two factors known to have potent effects on bone, prostaglandin E2 (PGE2) and transforming growth factor beta 1 (TGF-beta 1). MG-63 cells were cultured on Ti disks of varying roughness. The surfaces were ranked from smoothest to roughest: electropolished (EP), pretreated with hydrofluoric acid-nitric acid (PT), fine sand-blasted, etched with HCl and H2SO4, and washed (EA), coarse sand-blasted, etched with HCl and H2SO4, and washed (CA), and Ti plasma-sprayed (TPS). Cells were cultured in 24-well polystyrene (plastic) dishes as controls and to determine when confluence was achieved. Media were collected and cell number determined 24 h postconfluence. PGE2 and TGF-beta 1 levels in the conditioned media were determined using commercial radioimmunoassay and enzyme-linked immunosorbent assay kits, respectively. There was an inverse relationship between cell number and Ti surface roughness. Total PGE2 content in the media of cultures grown on the three roughest surfaces (FA, CA, and TPS) was significantly increased 1.5-4.0 times over that found in media of cultures grown on plastic or smooth surfaces. When PGE2 production was expressed per cell number, CA and TPS cultures exhibited six- to eightfold increases compared to cultures on plastic and smooth surfaces. There was a direct relationship between TGF-beta 1 production and surface roughness, both in terms of total TGF-beta 1 per culture and when normalized for cell number. TGF-beta 1 production on rough surfaces (CA and TPS) was three to five times higher than on plastic. These studies indicate that substrate surface roughness affects cytokine and growth factor production by MG-63 cells, suggesting that surface roughness may modulate the activity of cells interacting with an implant, and thereby affect tissue healing and implant success.

Somatostatin and cancer

The potential role of somatostatin (SRIF) in the diagnosis and treatment of nonendocrine human cancers is reviewed. There have been many reports of the growth-inhibitory activity of SRIF on normal and transformed cells in vitro. Many processes involved in malignant tumor growth depend on autocrine growth mechanisms, and somatostatin receptors (ssts) are present on many human cancers. It is possible that mutations in ssts result in a loss of check on proliferation in cancer cells. SRIF analogs may have a number of roles in clinical oncology. Use of radiolabeled tracers enables imaging of tumors bearing ssts; newer agents may enable positron emission tomography (PET) analyses or may be used to deliver lethal radiation doses to cells bearing a unique subset of sst. Although the ability of SRIF and its analogs to inhibit cellular proliferation has been shown in vitro, it has yet to be demonstrated in humans with cancer. Clinical improvements seen with SRIF or its analogs in cancer patients may be related to indirect effects, such as pain relief, reduction of gastrointestinal side effects of chemotherapeutic agents, effects on local production of growth factors, and inhibition of tumoral angiogenesis. Thus, with regard to their potential therapeutic role, SRIF analogs are likely to be used only in conjunction with other approaches, such as radiation, immunotherapy, chemotherapy, and growth factor modulation. Further research into the fundamental functions of each of the ssts and the intracellular actions of SRIF analogs will be needed to assess the potential usefulness of the latter in slowing the progression of human cancers.

Physiology of Puberty

Puberty is not a single event but one stage in development. The endocrine events of puberty in many ways recapitulate previous changes in the fetus. It is currently not known what triggers puberty at an appropriate time. It appears that puberty is restrained by higher central nervous system controls, but the restraint can be eliminated by injury or tumor growth resulting in premature puberty. The first endocrine event of puberty is an increase in the amplitude of gonadotropin pulses at night due to increased pulsatile release of hypothalamic gonadotropin-releasing hormone (GnRH) into the hypothalamic-pituitary portal system. This is reflected by an increase in luteinizing hormone secretion after a bolus of exogenous GnRH. Gonadal steroids are produced due to increased gonadotropin stimulation, and secondary sexual development follows a well-described pattern of changes. The pubertal growth spurt results from an increase in growth hormone secretion induced by sex steroids as well as from local production of growth factors. Positive feedback leads to the onset of menses and ovulation in girls by mid-puberty or later. This physical and reproductive maturity occurs in an orderly pattern, of which the physiology is described and in large part understood.

Formation-stimulating regimens other than sodium fluoride

Although no bone formation-stimulating regimen has been approved for treatment of established osteoporosis, there are a number of potentially effective drugs that are in various stages of preclinical and clinical testing. The two that show the greatest potential and the ones most likely to become available initially for clinical treatment are a parathyroid hormone fragment, PTH(1-34), and insulin-like growth factor-I. A promising approach for the future is to discover orally active agents that enhance the local production of growth factors by bone cells. It is likely that effective formation-stimulating regimens will become available for treating established osteoporosis within the next 5 years.

Regulation of insulin-like growth factor-I and its receptor in rat aorta after balloon denudation. Evidence for local bioactivity.

Local production of growth factors may play a major role in vascular repair after injury. We examined the regulation of insulin-like growth factor-I (IGF-I) and its specific membrane receptor in balloon-denuded rat aorta. Aortic IGF-I mRNA and radioimmunoassayable IGF-I content increased severalfold after balloon denudation with a peak at 7 d after injury. This coincided with a reciprocal 25% decrease in IGF-I receptor mRNA content and a 40% decrease in total 125I-IGF-I binding. Scatchard analysis indicated a single class of binding sites, with a decrease in receptor number at 7 d compared to control and no change in affinity. By in situ hybridization the predominant site of IGF-I expression in the normal and the denuded vessel wall was the medial smooth muscle cell. After denudation there was a relative decrease in IGF-I receptor mRNA in the medial cells as compared to the neointima, suggesting that the site of IGF-I action was predominantly in the medial layer. These data suggest that local expression and action of IGF-I are significant in the promotion of smooth muscle cell proliferation after arterial injury.

Basic fibroblast growth factor expression is regulated by corticotropin in the human fetal adrenal: a model for adrenal growth regulation.

Human fetal adrenal growth after midgestation is very rapid and appears to be dependent upon pituitary adrenocorticotropin (ACTH) in vivo. We hypothesized that the regulation of fetal adrenal growth by ACTH is mediated by ACTH-stimulated local growth factor production. As we have found basic fibroblast growth factor (bFGF) to be a potent mitogen for human fetal adrenal cells in culture, we conducted studies to determine whether bFGF is synthesized by the human fetal adrenal gland and whether bFGF gene expression in primary cultures of human fetal adrenal cells is regulated by ACTH. Bioassayable bFGF-like activity was detected in extracts of whole human fetal adrenal glands and primary cultures of human fetal adrenal cells. Northern blot analysis of total RNA from whole human fetal adrenal glands revealed a characteristic 7-kilobase bFGF mRNA, indicating that the fetal adrenal bFGF bioactivity was most likely due to local synthesis. Slot blot and ribonuclease protection analysis showed that bFGF mRNA was present in very low amounts in total RNA from primary cultures of unstimulated human fetal adrenal cells but was increased 2- to 3-fold in cells exposed to 10 nM ACTH-(1-24) or 1 mM 8-bromoadenosine 3',5'-cyclic monophosphate for 24 hr. bFGF mRNA was localized to adrenocortical cells and not fibroblasts by in situ hybridization. bFGF mRNA was barely detectable in unstimulated cells, whereas it was markedly increased in cells exposed to either ACTH or 8-bromoadenosine 3',5'-cyclic monophosphate. These data support our hypothesis that the regulation of human fetal adrenal growth by ACTH at midgestation may be mediated by the stimulation of local growth factor production, and we suggest that bFGF may play a major role in this process.

In Situ Expression of mRNA for Proto-Oncogenes in Benign Prostatic Hyperplasia and in Prostatic Carcinoma

Nine cases of prostatic carcinoma and 5 cases of benign prostatic hyperplasia (BPH) were examined for the in vivo expression of mRNA by an in situ hybridization technique for cellular proto-oncogenes, c-myc, c-fos, and c-sis. The latter of which encodes the B-chain of the platelet-derived growth factor (PDGF). High levels of c-myc and c-sis mRNAs were demonstrated in one highly differentiated prostatic carcinoma. Signals were localized in epithelial cells, both in packed cancer cells and in benign hyperplastic cells with glandular differentiation. A lower level of c-fos mRNA was also detected in the same areas. Four other carcinoma specimens showed c-sis mRNA, three of which also expressed c-fos mRNA. One other carcinoma expressed only c-myc mRNA. Three BPH specimens also contained c-sis and c-fos mRNA with one also exhibiting c-myc mRNA in the glandular epithelial cells. The results support the possibility that local production of growth factors, i.e. PDGF, may play a role in proliferation of prostatic epithelial cells.

Mode of action of pituitary growth hormone on target cells.

Normal postnatal somatic growth becomes progressively dependent on GH with time. In contrast to other hormones, GH is the only hormone known to produce a dose-dependent stimulation of postnatal growth. Most of the effects attributed to GH action appear to be the result of a direct effect of GH on cells in different peripheral tissues, including cartilage. In addition to the growth-stimulating effect, GH has the intrinsic properties of being able to exert both insulin-like and insulin-antagonistic effects in adipose tissue and skeletal muscle. These two apparently antagonistic effects seem to be explained by the stage of responsiveness of the target cells to GH, which is determined by the previous influence of endogenous GH. An inhibition of adenylate cyclase with a concomitant decrease in intracellular cAMP might be an important early cellular event in the course of GH action, but it is not known whether or how this change in nucleotide metabolism relates to the various expressed effects of the hormone. The recognition that GH directly interacts with chondrocytes in cartilage suggests that alterations in the concentration of circulating somatomedins cannot be the only factor regulating skeletal growth. The recent discovery by Green and coworkers (42) demonstrating that GH specifically stimulates the differentiation of cloned preadipose cells and myoblasts in tissue culture may be a major breakthrough in the understanding of the mechanism of action of the growth-promoting effect of GH. Green (42) has proposed that GH directly stimulates terminal differentiation of cells in many different tissues including epiphyseal plate cartilage. The finding that GH binds specifically to cells in the resting cell zone but not to differentiated chondrocytes in the growth plate suggests that prechondrocytes in the growth plate are the target cells for GH action. If it is correct that GH directly stimulates the differentiation of prechondrocytes, we suggest that, during the process of chondrocyte differentiation in the growth plate, the genes that code for growth factors of the somatomedin class, such as IGF-I, are expressed. As a consequence, the clonal expansion of the chondrocytes in the proliferative zone of the growth plate that occurs in vivo during the process of normal growth is the result of this local production of growth factors.