Osteopontin deficiency produces osteoclast dysfunction due to reduced CD44 surface expression

Osteopontin (OPN) was expressed in murine wild-type osteoclasts, localized to the basolateral, clear zone, and ruffled border membranes, and deposited in the resorption pits during bone resorption. The lack of OPN secretion into the resorption bay of avian osteoclasts may be a component of their functional resorption deficiency in vitro. Osteoclasts deficient in OPN were hypomotile and exhibited decreased capacity for bone resorption in vitro. OPN stimulated CD44 expression on the osteoclast surface, and CD44 was shown to be required for osteoclast motility and bone resorption. Exogenous addition of OPN to OPN-/- osteoclasts increased the surface expression of CD44, and it rescued osteoclast motility due to activation of the alpha(v)beta(3) integrin. Exogenous OPN only partially restored bone resorption because addition of OPN failed to produce OPN secretion into resorption bays as seen in wild-type osteoclasts. As expected with these in vitro findings of osteoclast dysfunction, a bone phenotype, heretofore unappreciated, was characterized in OPN-deficient mice. Delayed bone resorption in metaphyseal trabeculae and diminished eroded perimeters despite an increase in osteoclast number were observed in histomorphometric measurements of tibiae isolated from OPN-deficient mice. The histomorphometric findings correlated with an increase in bone rigidity and moment of inertia revealed by load-to-failure testing of femurs. These findings demonstrate the role of OPN in osteoclast function and the requirement for OPN as an osteoclast autocrine factor during bone remodeling.

T cell activation induces human osteoclast formation via receptor activator of nuclear factor kappaB ligand-dependent and -independent mechanisms

In unstimulated conditions, osteoclast (OC) formation is regulated by stromal cell production of the key osteoclastogenic factors receptor activator of nuclear factor kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). However, the mechanisms of accelerated osteoclastogenesis and bone loss characteristic of inflammatory conditions are poorly understood but appear to involve T cells. In addition, the mechanism by which OCs arise spontaneously in cultures of peripheral blood mononuclear cells in the absence of stromal cells or added cytokines remains unclear. Using a stromal cell free human osteoclast generating system, we investigated the ability of activated T cells to support osteoclastogenesis. We show that when activated by phytohemagglutinin-P (PHA), T cells (both CD4+ and CD8+) stimulate human OC formation in vitro. Although both soluble M-CSF and RANKL were detected in activated T cell supernatants, the presence of M-CSF was not essential for macrophage survival or RANKL-dependent osteoclast formation, suggesting that other soluble T cell-derived factors were capable of substituting for this cytokine. We also found that saturating concentrations of osteoprotegerin (OPG) failed to neutralize 30% of the observed OC formation and that T cell conditioned medium (CM) could superinduce osteoclastogenesis in cultures of purified monocytes maximally stimulated by RANKL and M-CSF. Together, these data suggest that activated T cells support osteoclastogenesis via RANKL-dependent and -independent mechanisms. Although not relevant for T cell-induced osteoclastogenesis, secretion of soluble M-CSF is a previously undescribed property of activated T cells.

Interleukin-7 stimulates osteoclast formation by up-regulating the T-cell production of soluble osteoclastogenic cytokines

In unstimulated conditions osteoclast renewal occurs as a result of the stromal cell production of the key osteoclastogenic factors, receptor activator of NFkB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). Inflammation is known to cause increased osteoclastogenesis; however, the mechanisms responsible for this phenomenon are poorly understood. We now show that interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha), cytokines typically produced in inflammatory conditions, increase the stromal cell production of IL-7. This factor, in turn, up-regulates production of osteoclastogenic cytokines by T cells leading to stimulation of osteoclast (OC) formation. Although T cells were found to produce soluble forms of both RANKL and M-CSF, saturating concentrations of osteoprotegerin failed to inhibit approximately 40% of the OC formation, suggesting that IL-7 acts via both RANKL-dependent and RANKL-independent pathways. Despite the identification of T-cell-secreted M-CSF, this cytokine was not essential for either RANKL-dependent or -independent OC formation, suggesting that T cells secrete other cytokines capable of substituting for M-CSF action. On the basis of our data, we propose a novel mechanism for inflammatory bone loss in which induction of IL-7 from stromal cells by IL-1 and TNFalpha leads to the production of soluble osteoclastogenic cytokines by T cells. Thus, the mechanism by which IL-7 causes bone resorption involves the activation of T cells and the T-cell-dependent augmentation of osteoclastogenesis. (Blood. 2000;96:1873-1878)

A novel T cell cytokine stimulates interleukin-6 in human osteoblastic cells

Rheumatoid arthritis (RA) is an autoimmune disease characterized by a heavy lymphocytic infiltration into the synovial cavity, resulting in the secretion of a variety of cytokines which ultimately leads to destruction of joint tissue. Among the infiltrating cells are activated T cells which produce specific cytokines capable of osteoclast progenitor cell expansion, fusion, and activation. Cultures of activated human T cells and human osteoblasts (hOBs) were used to study the possibility that lymphokines may act on osteoblasts to produce the osteoclastogenic factor interleukin-6 (IL-6). Purified T cells were activated with a combination of anti-CD3 and anti-CD28 antibodies, cocultured with hOBs in direct physical contact or separated by a transwell system, and conditioned media (CM) were assayed for IL-6 production. After a 72 h incubation period, activated T cell-hOB interaction resulted in a 100-fold increase of IL-6 production over basal levels. The immunosuppressant cyclosporine A (CsA) inhibited T cell tumor necrosis factor alpha and IL-6 production but did not inhibit the T cell induction of IL-6 from hOB. Assay of activated T-cell CM on hOB revealed that a soluble factor, not cell-cell contact, was the major inducer of IL-6. The induction of IL-6 mRNA by both activated T cell CM and CsA-treated activated T cell CM was confirmed by Northern blot analysis. Neutralizing antibodies to IL-13 and IL-17 did not affect IL-6 production. These findings suggest that activated T cells produce a novel, potent, IL-6 inducing factor that may be responsible for the bone loss observed in RA patients.

Skeletal casein kinase activity defect in the HYP mouse

The Hyp mouse, a model for human X-linked hypophosphatemia (XLH), is characterized by phosphate wasting and defective mineralization. Since osteopontin (OPN) is considered pivotal for biological mineralization, we examined the biosynthesis of OPN in osteoblasts of +/Y and Hyp/Y mice. Immunoprecipitation analyses using a specific antibody to OPN revealed that Hyp/Y and +/Y osteoblasts secrete similar levels of OPN as determined by [35S]-methionine biosynthetic labeling, but a reduced phosphorylation was noted after 32P-PO4 biosynthetic labeling. Northern blot hybridization analysis of +/Y and Hyp/Y mice osteoblast mRNAs, using a cDNA probe for mouse OPN, revealed no difference in the steady state levels of osteopontin mRNA. Analysis of casein kinase II activity in +/Y and Hyp/Y mice osteoblast, kidney, heart and liver membrane fractions revealed that casein kinase II activity in the Hyp/Y mice osteoblasts and kidney is only 35%-50%, respectively, of that of the +/Y mice tissues. The accumulated data are consistent with a post-translation defect in the Hyp/Y mouse osteoblast which results in the under-phosphorylation of osteopontin and subsequent under-mineralization of bone matrix.

Gestational exposure to ethanol suppresses msx2 expression in developing mouse embryos

Ethanol acts as a teratogen in developing fetuses causing abnormalities of the brain, heart, craniofacial bones, and limb skeletal elements. To assess whether some teratogenic actions of ethanol might occur via dysregulation of msx2 expression, we examined msx2 expression in developing mouse embryos exposed to ethanol on embryonic day (E) 8 of gestation and subjected to whole mount in situ hybridization on E11-11.5 using a riboprobe for mouse msx2. Control mice exhibited expression of msx2 in developing brain, the developing limb buds and apical ectodermal ridge, the lateral and nasal processes, olfactory pit, palatal shelf of the maxilla, the eye, the lens of the eye, otic vesicle, prevertebral bodies (notochord), and endocardial cushion. Embryos exposed to ethanol in utero were significantly smaller than their normal counterparts and did not exhibit expression of msx2 in any structures. Similarly, msx2 expression, as determined by reverse transcription-PCR and Northern blot hybridization, was reduced approximately 40-50% in fetal mouse calvarial osteoblastic cells exposed to 1% ethanol for 48 hr while alkaline phosphatase was increased by 2-fold and bone morphogenetic protein showed essentially no change. Transcriptional activity of the msx2 promoter was specifically suppressed by alcohol in MC3T3-E1 osteoblasts. Taken together, these data demonstrate that fetal alcohol exposure decreases msx2 expression, a known regulator of osteoblast and myoblast differentiation, and suggest that one of the "putative" mechanisms for fetal alcohol syndrome is the inhibition of msx2 expression during key developmental periods leading to developmental retardation, altered craniofacial morphogenesis, and cardiac defects.

Comparison of 22-oxacalcitriol and 1,25(OH)2D3 on bone metabolism in young X-linked hypophosphatemic male mice

Using a mouse model (Hyp) of human hypophosphatemic vitamin D-resistant rickets [X-linked hypophosphatemia (XLH)], we compared the effects of 22-oxa-1,25-dihydroxyvitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on restoring defects in mineral and skeletal metabolism. Hyp/Y mice received OCT or 1,25(OH)2D3 at doses of 0.05-0.25 micron.kg-1.day-1 for 4 wk. OCT normalized serum calcium levels, whereas 1,25(OH)2D3 produced hypercalcemia in Hyp/Y. OCT and 1,25(OH)2D3 also normalized serum phosphate levels and increased urinary calcium levels. Additionally, OCT and 1,25(OH)2D3 reduced elevated urinary pyridinoline levels and suppressed urinary adenosine 3',5'-cyclic monophosphate levels to normal. Bone ash content was low in Hyp/Y, and OCT was more effective than 1,25(OH)2D3 in reversing this defect. Histomorphometric analysis of bone turnover, mineralization rate, and osteoid content demonstrated comparable responses with OCT and 1,25(OH)2D3, although the highest dose of 1,25(OH)2D3 resulted in increased osteoid content and delayed mineralization. OCT appears to be more effective and definitely less toxic than 1,25(OH)2D3 in reversing skeletal lesions in Hyp/Y mice and may prove to be the drug of choice in the treatment of childhood XLH.

Production of interleukin-6 in human osteoblasts and human bone marrow stromal cells: evidence that induction by interleukin-1 and tumor necrosis factor-alpha is not regulated by ovarian steroids

Studies in murine models of osteoporosis have suggested the hypothesis that ovarian steroids may control osteoclastic bone remodeling by limiting the production of interleukin-6 (IL-6) from osteoblasts and bone marrow stromal cells. To investigate this hypothesis in a human model, we have examined 12 separate strains of normal human osteoblasts (HOB) and 11 separate strains of human bone marrow stromal cells (HBMSC) and determined whether ovarian steroids regulate the induction of IL-6 by interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha) or IL-1 + TNF. Treatment with IL-1, TNF or IL-1 + TNF resulted in the induction of IL-6 from both cell types with IL-1 + TNF inducing a synergistic induction of IL-6 in HOB (24- to 324-fold) and HBMSC (35-288 fold). Addition of 17 beta-estradiol or progesterone did not significantly alter IL-6 messenger RNA or protein levels in either HOB or HBMSC cultures stimulated with IL-1, TNF or IL-1 + TNF. Cultures incubated up to 96 h with the steroids did not affect IL-6 expression. Furthermore ovarian steroids did not affect IL-6 production in either HBMSC cultures representative of preosteoblasts or HOB cultures representative of highly differentiated osteoblasts. Specific chloramphenicol acetyl transferase assays and reverse transcriptase-polymerase chain reaction studies also demonstrated that the lack of an estrogen effect was not due to the failure of HOB to express functional estrogen receptors. Therefore, we conclude that the regulation of human osteoclastic bone remodeling by ovarian steroids does not occur through the direct regulation of IL-6 gene transcription or protein secretion in either early stages of osteoblast differentiation or the differentiated osteoblast.

Altered osteoblast gluconeogenesis in X-linked hypophosphatemic mice is associated with a depressed intracellular pH

We have studied gluconeogenesis and intracellular pH levels in normal (+/Y) and X-linked hypophosphatemic (Hyp/Y) mice. Compared with +/Y littermates, Hyp/Y mouse osteoblasts showed a higher rate of glucose production from fructose (10-fold), glutamine, and malate, but no significant difference when alpha-ketoglutarate was used as substrate. The activities of the pentose cycle enzymes, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase, were not different in the two osteoblast preparations. Examination of intracellular pH (pHi) using the double excitation of the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM) revealed a significantly lower pHi in Hyp/Y mouse osteoblasts compared with +/Y mouse osteoblasts (7.01 +/- 0.03 n = 10 versus 7.15 +/- 0.04 n = 8, respectively; P < 0.05). These results show for the first time that osteoblasts are capable of glucose production and that glucose production is altered in the Hyp/Y mouse osteoblast. As altered gluconeogenesis has been associated with reduced intracellular pH in other systems, a similar mechanism may be operative in the Hyp/Y mouse osteoblast. The observed defects may be intrinsic to the Hyp phenotype as the alterations in intracellular pH and gluconeogenesis persisted in vitro, or they may represent impressed memory from the in vivo state and the presumed circulating factor that influences phosphate transport.

X-linked hypophosphatemic rickets and the murine Hyp homologue

Recent studies have reported the cloning of several sodium-dependent phosphate cotransport proteins from the apical membrane of proximal tubules of several species. The human proximal tubule apical sodium-phosphate cotransport protein maps to chromosome 5 in the 5q35 region, indicating that this gene is not a candidate for the genetic defect leading to X-linked hypophosphatemia (XLH). Studies in what is thought to be the murine XLH homologue, Hyp, also indicate that the proximal tubular phosphate cotransporter gene does not map to the X chromosome. In Hyp, message levels for the apical membrane sodium cotransport protein are reduced by approximately 50%, similar to the reductions in the apical membrane protein levels of the transporter. This indicates a potential transcriptional defect in Hyp, leading to underexpression of the sodium-dependent phosphate transport protein. Recent studies in the Hyp osteoblast have characterized the intrinsic abnormalities of the cell leading to the osteomalacia characteristic of both Hyp and XLH. These studies demonstrate that the Hyp osteoblast expresses normal rates of phosphate transport, but altered gluconeogenesis similar to the proximal tubule, and that there is an underphosphorylation of an important matrix protein, osteopontin. Since osteopontin is involved in matrix mineralization, defective posttranslational modification of the protein could be a factor in producing the osteomalacia of the Hyp. Other recent studies have demonstrated improved modalities of treatment for Hyp and potentially for XLH. These involve the use of phosphate and nonhypercalcemic analogues of 1 alpha,25-dihydroxyvitamin D3. Thus, although the detection of the genetic defect producing XLH and Hyp is awaited, significant advances in the characterization of the phenotype and the bone abnormalities continue.

Phosphate transport in osteoblasts from normal and X-linked hypophosphatemic mice

Human hypophophatemic vitamin D-resistant rickets (X-linked hypophosphatemia-XLH) is characterized by hypophosphatemia, a decreased tubular reabsorption of phosphate (P(i)) and defective skeleton mineralization. Utilizing a mouse model (Hyp) of XLH, which demonstrates biological abnormalities and skeletal defects of XLH, we analyzed sodium-dependent phosphate transport in isolated osteoblasts derived from the calvaria of normophosphatemic and hypophosphatemic mice. Initial rates of phosphate uptake by normal and Hyp osteoblasts showed similar slopes. Osteoblasts from both normal and Hyp mice exhibited saturable, sodium-dependent phosphate transport with apparent Vmax and Km values not significantly different (normal mice, Vmax = 24.30 +/- 3.45 nmol/mg prot. 10 min, Km = 349.49 +/- 95.20 mumol/liter; Hyp mice, Vmax = 23.03 +/- 3.41 nmol/mg prot. 10 min, Km = 453.64 +/- 106.93 mumol/liter, n = 24). No differences were found in the ability of normal and Hyp osteoblasts to respond to P(i) transport after 5 hours of P(i) deprivation. Both cell types exhibited a similar increase in cAMP in response to PTH. The accumulated results demonstrate that P(i) uptake and transport in normal and Hyp mouse osteoblasts is a sodium-dependent saturable process. As osteoblast P(i) uptake and transport is apparently normal in the Hyp mouse model of XLH, the "osteoblastic failure" described for the Hyp mouse should be attributed to other mechanism(s).

Expression of metalloproteinases and tissue inhibitors of metalloproteinases in human osteoblast-like cells: differentiation is associated with repression of metalloproteinase biosynthesis

To more clearly define the expression of metalloproteinases and tissue inhibitors of metalloproteinases (TIMPs) within the human osteoblast (hOB) lineage, normal hOB and human osteogenic sarcoma cells possessing various levels of alkaline phosphatase (a marker of commitment to the osteoblast lineage) were treated with bone-resorbing agents to determine their effect on the production of interstitial collagenase, stromelysin, 72-kilodalton (kDa) gelatinase, 92-kDa gelatinase, TIMP-1, and TIMP-2. The results revealed that 1) normal hOB release copious amounts of 72-kDa gelatinase, TIMP-1, and TIMP-2; 2) hOB production of 72-kDa gelatinase and TIMP-2 is not regulated by agents that promote bone resorption (e.g. phorbol-12-myristate 13-acetate, recombinant human interleukin-1 beta, tumor necrosis factor-alpha, PTH, and vitamin D3); 3) normal hOB fail to secrete collagenase, stromelysin, or 92-kDa gelatinase when cultured on plastic or a type I collagen substratum, even in response to bone-resorptive agents or mononuclear cell-conditioned medium; 4) in contrast, certain of the osteogenic sarcoma cell populations produce collagenase, stromelysin, and 92-kDa gelatinase, especially when exposed to bone-resorbing stimuli; 5) in general, the capacity for metalloenzyme production by osteogenic sarcoma cell lines varies inversely with their alkaline phosphatase expression; and 6) the most committed (highest alkaline phosphatase) osteogenic sarcoma cell line, SAOS-2, precisely mimics the metalloproteinase profile of normal hOB. The results suggest that the expression of most metalloproteinases is under strict repression within the differentiated normal hOB, and cellular development is associated with diminished capacity to elaborate such enzymes.

Differentiation of human bone marrow osteogenic stromal cells in vitro: induction of the osteoblast phenotype by dexamethasone

Human bone marrow stromal cells were examined for their osteogenic potential in an in vitro cell culture system. Dexamethasone (Dex) treatment induced morphological transformation of these cells from an elongated to a more cuboidal shape, increased their alkaline phosphatase activity and cAMP responses to PTH and prostaglandin E2, and was essential for mineralization of the extracellular matrix. Dex-induced differentiation of human bone marrow stromal cells was apparent after 2-3 days of treatment and reached a maximum at 7-14 days, as judged by alkaline phosphatase activity, although induction of osteocalcin by 1,25-dihydroxyvitamin D3 was attenuated by Dex. Withdrawal of Dex resulted in an enhancement of the 1,25-dihydroxyvitamin D3-induced secretion of osteocalcin, whereas alkaline phosphatase activity and the cAMP response to PTH remained at prewithdrawal levels. The steady state mRNA level of osteonectin was not affected by Dex. Our results, which demonstrate that Dex conditions the differentiation of human bone marrow osteogenic stromal cells into osteoblast-like cells, support the hypothesis of a permissive effect of glucocorticoids in ensuring an adequate supply of mature osteoblast populations. Furthermore, the established human bone marrow stromal cell culture provides a good model of an in vitro system to study the regulation of differentiation of human bone osteoprogenitor cells.

Monocytic secretion of interleukin-1 receptor antagonist in normal and osteoporotic women: effects of menopause and estrogen/progesterone therapy

Interleukin-1 (IL-1), a potent stimulant of bone resorption, has been implicated in the pathogenesis of postmenopausal osteoporosis, because monocyte IL-1 bioactivity increases after the menopause and is decreased by estrogen and progesterone (EP) replacement. As IL-1 bioactivity reflect the production of both IL-1 and the IL-1 inhibitor, IL-1 receptor antagonist (IL-1ra), EP treatment could decrease IL-1 bioactivity by regulating the secretion of either IL-1 or IL-1ra. We now report that EP treatment in vivo decreased the secretion into the medium of cultured monocytes of IL-1ra and IL-1 beta as well as the IL-1 beta/IL-1ra ratio. We also found that in normal women the production of IL-1ra was within premenopausal levels in the first 7 yr after the menopause and increased linearly thereafter. In these women, monocyte IL-1 beta, IL-1 beta/IL-1ra ratio, and IL-1 bioactivity were all increased in the first 7 yr after the menopause and within the premenopausal range thereafter. In osteoporotic women, IL-1 beta, IL-1 beta/IL-1ra ratio, and IL-1 bioactivity increased after the menopause and returned to premenopausal levels after 15 yr from the menopause. In these women monocyte IL-1ra secretion was above the premenopausal range at all times after the menopause, but did not change with the passage of time since menopause. We conclude that hormone replacement decreases the in vitro secretion of both IL-1ra and IL-1 beta. The data also suggest that in normal women a progressive increase in the secretion of IL-1ra contributes to restore a normal IL-1/IL-1ra ratio after the menopause, a phenomenon which, in turn, may play a role in limiting postmenopausal bone loss.

Characterization of osteoblast-like cells from normal adult rat femoral trabecular bone

Osteoblast-like cell cultures have been established from the trabecular surfaces of normal adult rat femoral trabecular bone. The cultured cells responded to stimulation by parathyroid hormone (rPTH), with a rise in intracellular cAMP in excess of 25-fold while failing to respond to incubation with sCT. Furthermore, the osteoblast-like cells exhibited a high level of alkaline phosphatase expression, both histochemically and biochemically. Incubations with 1,25(OH)2 vitamin D3 increased the alkaline phosphatase activity by 50% and stimulated bone Gla-protein (BGP) synthesis. When the cell layers were supplemented with both 50 micrograms/ml ascorbic acid and 10 mM beta-glycerophosphate and allowed to grow past confluency for 3 weeks, they formed calcified ridges and multilayered nodules. Confirmation of the mineralization of an extracellular matrix was made by von Kossa staining. This simple isolation technique now facilitates the availability of normal adult rat osteoblastic cells for investigation of bone and mineral metabolism.

Evidence for interleukin-1 beta production by cultured normal human osteoblast-like cells

To determine if bone cells produce interleukin-1 beta (IL-1 beta), a potent bone resorption-stimulating agent, we studied well-characterized, nearly homogeneous cultures of normal human osteoblast-like (hOB) cells. With four strains of such cells, vehicle-treated cultures produced minimal IL-1 beta (mean +/- SEM, 1.3 +/- 0.3 pg/ml per 10(6) cells per 24 h) and showed dose-dependent (r = 0.99) increases to 2.2 +/- 0.7, 5.0 +/- 0.9, or 17.8 +/- 6.7 pg/ml, respectively, after treatment with lipopolysaccharide (LPS) at 3, 10, or 30 micrograms/ml (for increases after 10 and 30 micrograms/ml treatments, P less than 0.05). After treatment with tumor necrosis factor alpha (TNF-alpha) at 10 U/ml, IL-1 beta increased to 16.2 +/- 3.7 pg/ml (P less than 0.05). Neither 17 beta-estradiol nor bovine parathyroid hormone(1-34) (each at 10 nM), alone or in combination with LPS or TNF-alpha, affected IL-1 beta release. Northern blot analysis of total cellular RNA preparation revealed a single hybridization band at 1.9 kb when probed with a partially deleted cDNA for human IL-1 beta. The steady-state IL-1 beta mRNA levels showed a significant increase with LPS treatment and a lesser increase with TNF-alpha treatment in hOB cells. Moreover, TNF-alpha produced an even greater increase in IL-1 mRNA in HOBIT cells, a well-differentiated clonal cell line derived from normal hOB cells transfected with the SV40 large T antigen. We conclude that human cells of the osteoblast lineage produce IL-1 beta in response to well-recognized stimuli for IL-1 release from responsive tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone matrix constituents stimulate interleukin-1 release from human blood mononuclear cells

To test the hypothesis that mononuclear cells are stimulated to release interleukin 1 (IL-1) by bone fragments released in the bone microenvironment during the remodeling cycle, we have investigated the effects of bone matrix and some of its constituents on IL-1 secretin from peripheral blood mononuclear cells (PBMC). Increases in IL-1 activity were observed when either PBMC or adherent monocytes, but not lymphocytes depleted of monocytes, were co-cultured with either human or rat bone particles but not with latex particles of similar size. Co-culture of PBMC with bone particles in a transwell system where the cells were physically separated from the bone particles, or with osteoblast- or osteoclast-covered bone particles, did not stimulate IL-1 release, indicating that a physical contact between PBMC and the bone surface is required for eliciting IL-1 release. This was confirmed by the finding of a lower stimulatory effect of bone particles pretreated with etidronate, a bisphosphonate which decreases the bone binding capacity of PBMC. Constituents of bone matrix, such as collagen fragments, hydroxyproline, and, to a lesser extent, transforming growth factor-beta, but not osteocalcin, alpha 2HS glycoprotein, fragments of either bone sialoprotein or osteopontin, and fibronectin, stimulated PBMC IL-1 release in a dose-dependent fashion. Collagen-stimulated IL-1 release was partially and specifically inhibited by a monoclonal antibody directed against the alpha 2 beta 1-integrin cell surface collagen receptor. These data demonstrate that products of bone resorption, known to be chemotactic for mononuclear cells, stimulate PBMC IL-1 activity. These findings may help explain previous documentation of increased IL-1 secretion by circulating monocytes obtained from patients with high turnover osteoporosis.

Increased monocyte interleukin-1 activity and decreased vertebral bone density in patients with fasting idiopathic hypercalciuria

Idiopathic hypercalciuria (IH) is a heterogeneous disorder frequently observed in patients with nephrolithiasis. At one extreme of its clinical spectrum is fasting hypercalciuria (FH), a condition characterized by increased bone resorption and turnover. In previous studies we have shown that monocytes from patients with high turnover osteoporosis and from women in early postmenopause elaborate increased amounts of interleukin-1 (IL-1), a cytokine that stimulates bone resorption in vitro and in vivo. Since IL-1 could also mediate the resorptive mechanism of FH and cause a clinically significant bone loss, we have studied the relationship of IH, vertebral mineral density, bone turnover, and monocyte IL-1 activity in 47 patients with absorptive hypercalciuria (AH), 23 with FH, and 38 nonhypercalciuric subjects with recurrent nephrolithiasis (controls). Vertebral mineral density, as measured by quantitative computer tomography, was decreased in each of the three patient groups, but was significantly lower in FH patients than in AH patients or control subjects. Twenty-four-hour total urinary hydroxyproline excretion was increased in FH patients compared to that in AH patients or controls, but blood levels of osteocalcin were not. Monocytes from FH subjects yielded significantly more IL-1 (alpha + beta) activity than those from AH patients or controls; levels of IL-1 activity in monocytes of AH and control patients were similar. In IH subjects, significant correlations were found between IL-1 and hydroxyproline (r = 0.70; P less than 0.0001), IL-1 and quantitative computer tomography values (r = -0.49; P less than 0.005), and IL-1 and urinary calcium (r = -0.36; P less than 0.05). Serum PTH levels were within normal limits in all subjects and were similar in the three study groups, 1,25-Dihydroxyvitamin D3 levels, although higher in IH patients than in controls, were not significantly different in FH and AH subjects. Increased IL-1 activity and decreased vertebral mineral density are features of a subset of patients with IH. Although a cause-effect relationship remains to be established, increased monocytic IL-1 activity, rather than elevated PTH or 1,25-dihydroxyvitamin D3 levels, could underlie the resorptive component of FH.

The role of interleukin-1 in postmenopausal bone loss

Interleukin-1 (IL-1), a cytokine best known for its ability to stimulate lymphocyte proliferation, has recently been shown to stimulate bone resorption and modulate bone formation in vivo. Consequently, the authors have devised a series of studies to investigate the relationship between bone remodeling, menopause, and monocyte IL-1-secretion. In a first study, monocytes from osteoporotic patients were found to produce more IL-1 than monocytes from control subjects. IL-1 activity was also found to reflect histomorphometric indices of bone formation, but not of bone resorption. In a second study, devised to assess the effect of menopause on the relationship between IL-1 and bone turnover, a significant correlation was found between IL-1 and BGP in premenopausal osteoporotic women and osteoporotic men, but not in both postmenopausal osteoporotic subjects and normal subjects of either sex. In a third study, IL-1 from untreated postmenopausal women was found to be higher than in either untreated premenopausal or estrogen/progesterone-treated postmenopausal women. A significant negative correlation was found between IL-1 and years since menopause in both the healthy and osteoporotic postmenopausal women. Premenopausal IL-1 levels were achieved within eight years of menopause in the healthy but not in the osteoporotic subjects. In osteoporotic women, high IL-1 levels were evident as long as 15 years after menopause. IL-1 also correlated inversely with mineral density as measured by quantitative computer tomography. In prospective study, treatment with estrogen/progesterone caused a significant increase in IL-1 activity. This data indicates that monocyte IL-1 production mirrors the rate of bone turnover in both the healthy and osteoporotic patient, and that alteration in IL-1 production may underlie the postmenopausal acceleration of bone loss and its inhibition by ovarian steroids.

Human osteoblasts in vitro secrete tissue inhibitor of metalloproteinases and gelatinase but not interstitial collagenase as major cellular products

Human osteoblast cultures (hOB) were examined for the production of interstitial collagenase, tissue inhibitor of metalloproteinases (TIMP), and gelatinolytic enzymes. Cells were isolated by bacterial collagenase digestion of trabecular bone (vertebra, rib, tibia, and femur) from 11 subjects (neonatal to adult). Confluent cultures were exposed to phorbol 12-myristate 13-acetate, PTH, PGE2, epidermal growth factor, 1,25(OH)2 vitamin D3, recombinant human IL-1 beta, and dexamethasone. Collagenase and TIMP were assayed immunologically and also by measurements of functional activity. Collagenase was not secreted in significant quantities by human bone cells under any tested condition. Furthermore, collagenase mRNA could not be detected in hOB. However, hOB spontaneously secreted large amounts of TIMP for at least 72 h in culture. hOB TIMP was found to be identical to human fibroblast TIMP by double immunodiffusion, metabolic labeling and immunoprecipitation, Northern blot analysis, and stoichiometry of collagenase inhibition. SDS-substrate gel electrophoresis of hOB-conditioned media revealed a prominent band of gelatinolytic activity at 68 kD, and specific polyclonal antisera established its identity with the major gelatinolytic protease of human fibroblasts. Abundant secretion of gelatinolytic, but not collagenolytic, enzymes by hOB may indicate that human osteoblasts do not initiate and direct the cleavage of osteoid collagen on the bone surface, but may participate in the preparation of the bone surface for osteoclast attachment by removal of denatured collagen peptides. The constitutive secretion of TIMP may function to regulate metalloproteinase activity.

Ovarian steroid treatment blocks a postmenopausal increase in blood monocyte interleukin 1 release

In previous studies, we showed that blood monocyte elaboration of interleukin 1 (IL-1), a known stimulator of bone resorption, was higher in osteoporotic patients with rapid bone turnover than in those with slow turnover and in nonosteoporotic subjects. Since an acceleration of bone loss following menopause contributes to the risk of osteoporosis in women, we have studied the effects of menopause and ovarian steroid treatment on IL-1 release by monocytes obtained from nonosteoporotic and osteoporotic women. IL-1 activity in the monocyte culture medium derived from untreated postmenopausal women (nonosteoporotic and osteoporotic) was higher than in the medium derived from either untreated premenopausal or estrogen/progesterone-treated postmenopausal women. A significant negative correlation was found between IL-1 and years since menopause in both the healthy (r = -0.75; P less than 0.005) and the osteoporotic (r = -0.61; P less than 0.01) untreated postmenopausal women. The difference between the two slopes was significant at P less than 0.05. Premenopausal IL-1 levels were achieved within 8 years of menopause in the nonosteoporotic, but not in the osteoporotic, subjects in whom increases were evident as long as 15 years after menopause. IL-1 also correlated inversely with vertebral mineral density (r = -0.37; P less than 0.05), as measured by quantitative computed tomography. In prospective studies, treatment with estrogen/progesterone for 1 month caused a substantial highly significant decrease in IL-1 activity in each of three nonosteoporotic and five osteoporotic women, confirming the apparent effect of hormone therapy observed in the cross-sectional analysis. Although a cause-effect relationship has not been established, it is our hypothesis, based on these data, that alterations in IL-1 production may underlie the postmenopausal acceleration in bone loss and its inhibition by ovarian steroids. Persistent elevation of IL-1 secretion appears to be a feature of postmenopausal osteoporosis.

Monokines produced by macrophages stimulate the growth of osteoblasts

We have previously reported that the J774A.1 macrophage-like tumor cell line produces two potent monokines which stimulate the growth of osteoblasts and chondrocytes. These growth factors, which have an affinity for heparin-agarose, have been termed HEP I (a 30 Kd PDGF-like molecule) and HEP II (an approximately 20 Kd molecule), respectively, based on their elution profile. Unlike HEP I, HEP II does not stimulate the growth of fibroblasts. Extensive biological and chromatographic studies disclosed that HEP II appears to be a unique bone cell mitogen unlike any known growth factor, including the FGFs, IL-1s, and TNFs, EGF, IGF-I and -II, TGF-beta, beta 2 microglobulin, G-CSF, CSF-1 and GM-CSF. To characterize more fully the effects of the macrophage-derived monokines on osteoblast growth and function, clones were derived from calvaria explant cultures. Two clones, SDFRC-2.05 and SDFRC-3, were developed and found to exhibit osteoblastic characteristics, including high levels of alkaline phosphatase, synthesis of type I but not type III collagen, and an increased intracellular cAMP production in response to PTH. The SDFRC-3 cells exhibited a polygonal morphology like that of the explant-derived cells while SDFRC-2.05 cells exhibited a more fibroblastic morphology. When tested on the explant cultures and clones, HEP I and HEP II were found to stimulate DNA synthesis and increase protein per culture, but decreased alkaline phosphatase activity. Clone SDFRC-3 was found to be more responsive to HEP II than clone SDFRC-2.05. Both monokines were found to be more potent mitogens for bone cells than TGF-beta. HEP II, but not HEP I or TGF-beta, induced a transformation of bone cells from a polygonal to a fibroblastic morphology, suggesting the induction of migration prior to proliferation. Thus, macrophages may be responsible not only for bone repair but also for ensuring the linkage of bone formation to resorption during physiological remodeling.

Purification and characterization of human myometrial smooth muscle collagenase

Collagenase has been purified from the culture medium of a human myometrial smooth muscle cell line, and the properties of the pure enzyme compared to those of collagenase from another human mesenchymal cell, the fibroblast. The smooth muscle collagenase was purified using a new, rapid, and convenient three-step purification procedure consisting of chromatography on iminodiacetate-agarose chelated with zinc and on Cibacron Blue-agarose followed by gel filtration on Ultrogel AcA-44. The resultant pure collagenase is secreted as a zymogen indistinguishable from that of the fibroblast enzyme in molecular weight, amino acid composition, and in the nature of its conversion to active enzyme by trypsin. The amino acid sequence of the two enzymes at the trypsin cleavage site is the same. The two collagenases are also indistinguishable immunologically and display essentially identical kinetic behavior on a variety of collagen substrates. Although the two collagenases appear to be identical proteins, the mechanisms which regulate their production appear to be very different. Glucocorticosteroids, which inhibit collagenase production in human skin fibroblasts are without effect in the uterine smooth muscle cell. In contrast, the smooth muscle cell appears to require a component present in fetal bovine serum in order to produce the enzyme.

Does interleukin-1 affect intracellular calcium in osteoblast-like cells (UMR-106)?

Interleukin-1 (IL-1) enhances bone resorption and formation in vitro, presumably through a primary action on osteoblasts, but the mechanism by which IL-1 activates bone cells is unknown. We investigated the possibility that the effect of IL-1 on osteoblasts is mediated through an increase in intracellular calcium [Ca++]i by studying the effects of purified human monocyte-derived IL-1 (hIL-1) and recombinant human IL-1 alpha (rhIL alpha) and beta (rhIL-1 beta) on [Ca++]i in the rat osteogenic sarcoma cell line UMR 106 using indo-1, a new-generation fluorescent Ca++-sensitive probe. hIL-1 (1 U/ml) resulted in an 85.5% rise in [Ca++]i over baseline that reached a peak after 30 seconds and returned to basal levels within 60 seconds. A similar transient rise in calcium was obtained upon exposure of the UMR cells to both the hIL-1 suspension buffer and to the concentration of fetal bovine serum present in the hIL-1 buffer. This effect was not abolished either by heat inactivation of both hIL-1 and serum or by pretreatment of hIL-1 with specific rabbit antihuman-IL-1 antibody. Moreover, exposure of the UMR cells to either rhIL-1 alpha or rhIL-1 beta or to a mixture of both at concentrations of 1 to 100 U/ml was not followed by any change in [Ca++]i. Our data do not support the idea that IL-1 can stimulate osteoblasts through a calcium-mediated pathway.

J774A.1 macrophage cell line produces PDGF-like and non-PDGF-like growth factors for bone cells

In light of evidence that macrophages participate in the local regulation of bone remodeling, we have examined the production of peptide stimulators of bone cell growth and specialization by the J774A.1 macrophage cell line. Cultured J774A.1 cells secrete growth-promoting activities which have an affinity for heparin. The first partially purified material, termed HEP I, appears to contain platelet-derived growth factor (PDGF)-like activity. It has a molecular weight of about 30,000 daltons, inhibits the binding of labeled PDGF to its receptors, reacts with polyclonal anti-human PDGF antibody, and exhibits mitogenic activity for osteoblasts, which is partially blocked by anti-PDGF antisera. Like PDGF, HEP I is active in a wide variety of mesenchyme-derived cells, including osteoblasts, chondrocytes, smooth muscle cells, fibroblasts, 3T3 cells and NRK cells. The J774A.1 cells contain mRNA, which hybridizes to a v-sis DNA probe, suggesting that they express the c-sis gene, which contains the code for a PDGF-like protein. The second factor, HEP II, has an approximate molecular weight of 20,000 daltons and possesses substantial mitogenic activity for osteoblasts, chondrocytes, and smooth muscle cells, but is not mitogenic for fibroblasts, 3T3 cells, and NRK cells. HEP II appears to be a unique bone cell mitogen, which is distinct from the growth factors presently known. Neither HEP I nor HEP II contained interleukin 1, a macrophage product known to promote bone resorption and perhaps the growth and activity of osteoblasts.

Spontaneous release of interleukin 1 from human blood monocytes reflects bone formation in idiopathic osteoporosis

Osteoporosis is a state of reduced skeletal mass characterized by various rates of bone remodeling. Multiple locally elaborated factors have been identified that appear to influence the cellular events in bone remodeling. The possible role(s) of these factors in the pathogenesis of osteoporosis is unknown. One such factor, interleukin 1 (IL-1), is of particular interest, as this protein is known to stimulate bone resorption and perhaps formation. Consequently, we have measured the spontaneous secretion of IL-1 activity by cultured peripheral blood monocytes obtained from 22 osteoporotic patients and 14 age-matched control subjects. Monocytes from osteoporotic patients produced more IL-1 than did monocytes from control subjects. When patients were grouped according to monocyte-produced IL-1 activity, dynamic parameters of bone formation, as judged by quantitative histomorphometric analysis of iliac crest bone biopsies and by circulating levels of bone 4-carboxyglutamic acid protein (BGP)--a marker of bone formation--were higher in subjects with elevated IL-1 activity; whereas, indices of bone resorption and static indices of bone formation were similar in subjects with either high or normal IL-1 activity. IL-1 activity released by peripheral blood monocytes appears to reflect bone formation rate in osteoporotic patients and may be of pathogenetic significance in a subset of individuals with osteoporosis.

Prostaglandins change cell shape and increase intercellular gap junctions in osteoblasts cultured from rat fetal calvaria

Mounting experimental evidence indicates that osteoblasts may be cellular intermediaries in the local activation of bone remodeling. To elucidate the role of these cells in activation, we examined the effects of prostaglandins (PGs), known resorption stimulators, on cell shape and intercellular junctional relationships in osteoblasts cultured from rat fetal calvaria. Exposure to PGE2 and PGE1, promoters of bone resorption, rapidly (within 20 min) converted the osteoblasts from a flattened to a stellate shape (shape change), and markedly increased the appearance of intercellular (gap) junctions within 10 min. Both effects were directly related to the prostaglandin concentration, as little as 1 nM being effective. PGE1, but not PGB1, PGF1 alpha, PGD2, and PGF2 alpha, mimicked the substantial effect of PGE2 on shape change. Shape change and gap junction formation appear to arise independently. PTH, an inducer of shape change, did not affect the number of gap junctions appreciably. Colchicine, a microtubule polymerization inhibitor, and trifluoperazine, an inhibitor of calmodulin action, blunted PGE2-mediated shape change but not the effect of PGE2 on gap junctions. Shape change and gap junction formation may be important events in local activation, shape changes in surface osteoblasts serving to expose bone surfaces which are chemotactic for osteoclasts and gap junctions propagating locally initiated activation messages.

Fetal rat chondrocytes sequentially elaborate separate growth- and differentiation-promoting peptides during their development in vitro

Chondrocytes isolated from the calvaria of rat fetuses proliferate and form cartilage when cultured in a chemically defined, serum-free medium, suggesting that they may elaborate self-regulatory factors. Conditioned media obtained from these chondrocytes stimulated DNA synthesis and proliferation when added to separate cultures of chondrocytes and the closely related osteoblast-like cells, but were not very effective in skin fibroblasts isolated from the same fetuses, as judged by [3H]thymidine incorporation and cell proliferation. Chondrocyte-conditioned medium also promoted chondrocyte differentiation, augmenting 35SO4 incorporation, and the accumulation of type II collagen and cartilage-specific proteoglycan. Stimulation of growth and differentiation appears to be attributable to separate activities, released into the medium sequentially by the cultured chondrocytes during their proliferation and maturation phases. Media obtained from growing chondrocytes stimulated growth, but had little effect on 35SO4 incorporation. Media obtained from mature cultures promoted growth as well as 35SO4 incorporation. The mitogenic and sulfation activities were trypsin inhibitable, but exhibited different solubility characteristics and striking differences in their patterns of elution from gel filtration columns. These results suggest that chondrocytes elaborate autostimulatory peptides, the biological activities of which mirror, at least in part, the developmental stage of the donor cells.

Macrophage-derived growth factor for osteoblast-like cells and chondrocytes

Rat resident peritoneal macrophages in primary culture were found to elaborate a mitogenic factor (or factors) for rat osteoblast-like cells and chondrocytes but not for skin fibroblasts. Growth-promoting activity appeared in the incubation medium within the first 20 hr of macrophage culture and was released in amounts that paralleled the number of macrophages per culture. After their proliferative response, as judged by increases in DNA synthesis and cell number, the osteoblast-like cells became enriched in alkaline phosphatase, an index of osteoblast specialization. The macrophage-derived activity was nondialyzable and heat-stable, and it was eliminated by exposure to trypsin. Inhibition of prostaglandin cyclooxygenase failed to modify its generation. Partial purification (Amicon filter concentration, gel filtration) disclosed principal peaks of activity corresponding to Mr of 43,000 and 10,000. The crude conditioned medium and the Mr 43,000-peak, but not the low-molecular-weight peak, exhibited interleukin 1 activity, as judged by the ability to stimulate the proliferation of mouse thymic lymphocytes. The macrophage-derived growth factor described herein may participate in bone remodeling and repair and in primary bone and cartilage growth.

Regulation of 25 hydroxyvitamin D3 1-hydroxylase in serum-free monolayer culture of mouse kidney

Primary monolayer cultures of cells from normal mouse kidney were initiated and maintained in serum-free medium supplemented with insulin, transferrin and prostaglandin E1. Renal epithelial cells grow to confluence without detectable growth of fibroblasts. These cells contain an active 25(OH)D3 1-hydroxylase with half-maximal formation of 1,25(OH)2D3 achieved at a substrate concentration of 13.3 nM. Activity of this enzyme is increased by low calcium medium or parathyroid hormone and decreased by high calcium medium, high phosphate medium or 1,25(OH)2D3.

Selective emergence of differentiated chondrocytes during serum-free culture of cells derived from fetal rat calvaria

Cells dispersed from the chondrocranial portions of fetal rat calvaria proliferated and performed specialized functions during primary culture in a chemically defined medium. Mature cultures were typified by multilayered clusters of redifferentiating cartilage cells. Flattened cells that lacked distinguishing features occupied areas between the clusters. Alkaline phosphate-enriched, ultrastructurally typical chondrocytes within the clusters were encased in a dense extracellular matrix that stained prominently for chondroitin sulfate proteoglycans. This matrix contained fibrils measuring 19 nm in diameter, which were associated with proteoglycan granules that preferentially bound ruthenium red. A progressive increase in the number of cells indicated the proliferation of certain elements in the primary culture. The cells in primary culture were biochemically as well as morphologically heterogeneous since they were found to synthesize type I and type II collagens. Homogeneous populations of redifferentiated chondrocytes were recovered as floating cells and were shown to express the chondrocyte phenotype in secondary culture. Subcultured cells synthesized type II collagen and its precursors almost exclusively and incorporated 35SO4 into proteoglycan monomer and aggregates to a greater degree than the cells in primary culture. The pattern of proteoglycan monomer and aggregate labeling resembled that of intact cartilage segments and bovine articular chondrocytes. Skin fibroblasts harvested from the same rat fetuses failed to proliferate when maintained under identical conditions. Hence, exogenous hormones, growth factors, and protein are not required for chondrocyte growth and maturation.

Presence of epidermal growth factor receptors and influence of epidermal growth factor on proliferation and aging in cultured smooth muscle cells

Epidermal growth factor (EGF) at nanomolar concentrations stimulated DNA synthesis in confluent, serum-starved cultures of calf aorta and human uterine smooth muscle cells. Stimulation of DNA synthesis in lens epithelial cells was studied for comparison. L and D-ascorbic acid potentiated the effect of serum and EGF on DNA synthesis in calf aorta cells. In contrast L-ascorbic acid had minimal potentiating effect with serum and no effect with EGF present along with serum on DNA synthesis in human uterine smooth muscle and rabbit lens epithelial cells. EGF and ascorbic acid increased cell number when added to stationary phase cultures. Specific binding of 125I-labelled EGF to smooth muscle cells was demonstrated. Receptor concentration in calf-aorta smooth muscle cells was higher in dense cultures compared to sparse cultures. The time course of binding and dissociation of 125I-labelled EGF was similar in "dense" and "sparse" cultures. Human uterine smooth muscle cells in culture exhibited a finite lifespan. There was no stimulation of DNA synthesis in response to serum and EGF in cells of high population doubling level (PDL); although 125I-labeled EGF binding was higher in old cells (high PDL) compared to young cells (low PDL). This increase in binding was shown to be due to changes in the concentration of receptors without changes in their affinity for EGF.

The characterization of human uterine smooth muscle cells in culture

Primary cultures initiated from normal human uterine endometrium after total enzymatic dissociation contained epithelioid cells and smooth muscle cells. The smooth muscle cells were subsequently isolated by differential trypsinization and grown in culture for 36 +/- 4 generations. Ultrastructural examination of log and post-confluent cultures of cells at low and high population doubling levels revealed characteristics similar to those of published reports on other smooth muscle cells studied in vivo and in vitro. Among the common features present were: (a) abundant bundles of 60--70 A myofilaments; (b) branched mitochondria; (c) stacks of cisternae of rough endoplasmic reticulum; (d) caveolae intracellulares; (e) nexuses. Other features included ovoid nuclei, a well developed Golgi apparatus and abundant free ribosomes. The subcultured cells exhibited features of dedifferentiation in the log phase of growth and at post-confluency. However, the post-confluent cells showed characteristics indicating redifferentiation back towards their in vivo morphology. Smooth muscle cells isolated from endometrial curettings may provide a useful model for biochemical and pharmacological studies of a cell type derived from a hormonal target tissue as the cells "age" in culture.

Regulation of cyclic nucleotide phosphodiesterase activity in human lung fibroblasts

Cyclic nucleotide phosphodiesterase activity (3', 5'-cyclic-nucleotide 5'-nucleotidohydrolase, 3.1.2.17) was studied in homogenates of WI-38 human lung fibroblasts using 0.1--200 microgram cyclic nucleotides. Activities were observed with low Km for cyclic AMP(2--5 micron) and low Km for cyclic GMP (1--2 micron) as well as with high Km values for cyclic AMP (100--125 micron) and cyclic GMP (75--100 micron). An increased low Km cyclic AMP phosphodiesterase activity was found upon exposure of intact fibroblasts to 3-isobutyl-1-methylxanthine, an inhibitor of phosphodiesterase activity in broken cell preparations, as well as to other agents which elevate cyclic AMP levels in these cells. The enhanced activity following exposure to 3-isobutyl-1-methylxanthine was selective for the low Km cyclic AMP phosphodiesterase since there was no change in activity of low Km cyclic GMP phosphodiesterase activity or in high Km phosphodiesterase activity with either nucleotide as substrate. The enhanced activity due to 3-isobutyl-1-methylxanthine appeared to involve de novo synthesis of a protein with short half-life (30 min), based on experiments involving cycloheximide and actinomycin D. This activity was also enhanced with increased cell density and by decreasing serum concentration. Studies of some biochemical properties and subcellular distribution of the enzyme indicated that the induced enzyme was similar to the non-induced (basal) low Km cyclic AMP phosphodiesterase.

gamma-Glutamyltransferase in human diploid fibroblasts and other mammalian cells

gamma-Glutamyltransferase was determined in WI-38 human diploid fibroblasts and compared to enzyme levels determined in several other mammalian cell lines including: fibroblast-like cells from human skin, tibia and foreskin; epithelial-like cells from human, bovine and monkey kidney; and transformed cells (Chinese hamster ovary, HeLa S3 and SV-40 transformed WI-38). Transformed cells had the lowest activity found followed in increasing order by fibroblasts, human and bovine epithelial cells and monkey kidney epithelial cells. The enzyme isolated from the plasma membrane of WI-38 cells, like the enzyme from kidney and brain, was found to be irreversibly inhibited by iodoacetamide, reversibly by serine-borate, and had a strong specificity for certain amino acids. The possibility exists that gamma-glutamyltransferase could be involved in transport of amino acids into cells in culture; and glutamine, used in media, is an excellent substrate for the enzyme.

Liver collagen synthesis in murine schistosomiasis

Collagen synthesis was measured in liver slices obtained from mice with hepatosplenic schistosomiasis. Enlarged fibrotic livers from these mice contained 20 times more collagen than normal. This model of hepatic fibrosis results from an inflammatory granulomatous host response to Schistosoma mansoni ova in portal tracts, rather than from direct lover cell injury as with carbon tetrachloride-induced liver fibrosis. Collagen synthesis, as measured by the formation of labeled protein-bound hydroxyproline, occurred in granulomas isolated from fibrotic livers. Labeled collagen that cochromatographed with type I collagen was extracted with neutral salt solution from liver slices incubated with labeled proline. The free proline pool of the liver was doubled in infected mice; coordinately, liver slices from these animals showed maximal collagen production when the concentration of free proline in the medium was raised to 0.4 mM, the same level measured in the fibrotic livers. Under such conditions, collagen synthesis was at a rate equivalent to the formation of 5.4 nmol of protein-bound hydroxyproline per g liver in 6 h. In comparative incubations in medium containing 0.2 mM proline, fibrotic liver slices produced 16-fold more collagen than normal slices. The proline analogue, L-azetidine 2-carboxylic acid, effectively inhibited synthesis of labeled collagen by fibrotic liver slices. These studies show the synthesis of collagen in a reproducible animal model of the most prevalent form of human liver fibrosis. Difinitition of the controlling factors in this system is of interest for the general problem of fibrosis produced by immunological responses.