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R L Jilka

Publications and source records attributed to R L Jilka.

At least 37 records · Page 2Linked to original sources
PubMed1997

Increased adipogenesis and myelopoiesis in the bone marrow of SAMP6, a murine model of defective osteoblastogenesis and low turnover osteopenia.

Bone formation and hematopoiesis are anatomically juxtaposed and share common regulatory mechanisms. However, little is known about the interrelationship between these two processes. We have previously shown that the senescence accelerated mouse-P6 (SAMP6) exhibits decreased osteoblastogenesis in the bone marrow that is temporally linked with a low rate of bone formation and decreased bone mineral density. Here we report that in contrast to decreased osteoblastogenesis, ex vivo bone marrow cultures from SAMP6 mice exhibited an increase in the number of colony-forming unit adipocytes, as well as an increase in the number of fully differentiated marrow adipocytes, compared with SAMR1 (nonosteopenic) controls. Further, long-term bone marrow cultures from SAMP6 produced an adherent stromal layer more rapidly, generated significantly more myeloid progenitors and produced more IL-6 and colony-stimulating activity. Consistent with this, the number of myeloid cells in freshly isolated marrow from SAMP6 mice was increased, as was the number of granulocytes in peripheral blood. The evidence that SAMP6 mice exhibit decreased osteoblastogenesis, and increased adipogenesis and myelopoiesis, strongly suggests that a switch in the differentiation program of multipotential mesenchymal progenitors may underlie the abnormal phenotype manifested in the skeleton and other tissues of these animals. Moreover, these observations support the contention for the existence of a reciprocal relationship between osteoblastogenesis and adipogenesis that may explain the association of decreased bone formation and the resulting osteopenia with the increased adiposity of the marrow seen with advancing age in animals and humans.

Adipocytes↗
PubMed1997

Quantification of vitamin D receptor mRNA by competitive polymerase chain reaction in PBMC: lack of correspondence with common allelic variants.

It has been recently claimed that polymorphism for the vitamin D receptor (VDR) influences several aspects of calcium and bone metabolism. To evaluate the physiologic plausibility of these claims, we compared the abundance of the VDR mRNA in peripheral blood mononuclear cells (PBMCs) between different VDR genotypes using a quantitative reverse transcribed polymerase chain reaction-based method. The method is based on the coamplification of VDR cDNA and an internal standard consisting of known concentrations of a human VDR CDNA mutated at a BglII restriction site; the interassay coefficient of variation is 11%. To validate the method, we made use of earlier receptor binding studies indicating that normal human monocytes and activated, but not resting, lymphocytes expressed the VDR. The concentration of the VDR mRNA was 10(-8) to 10(-7) g/g of total RNA in cell-sorted monocytes and in in vitro activated lymphocytes, but only 10(-12) g/g of total mRNA in resting lymphocytes, establishing that the VDR mRNA determined by our method in PBMCs is due to constitutive expression in monocytes. Following an initial genotype screening of 85 normal volunteers by polymerase chain reaction or restriction fragment length polymorphism analysis, 14 individuals with the Bb genotype, 12 with the bb genotype, and 12 with the BB genotype were selected. The concentration of the VDR mRNA, corrected for the number of monocytes, was similar among the three genotype groups, as were the other variables examined: serum calcitriol, serum osteocalcin, and vertebral and hip bone density. We conclude that VDR polymorphism does not affect the abundance of the VDR mRNA.

Aged↗
PubMed1996

Linkage of decreased bone mass with impaired osteoblastogenesis in a murine model of accelerated senescence.

Bone marrow is the principal site for osteoclastogenesis and osteoblastogenesis; and an increase in the former has been linked with bone loss caused by acute loss of gonadal steroids. We have now used an established murine model of accelerated senescence and osteopenia (SAMP6) to test the hypothesis that reduced osteoblastogenesis is linked with decreased bone mass. At 1 mo of age, the number of osteoblast progenitors in SAMP6 marrow was indistinguishable from controls; however a threefold decrease was found at 3-4 mo of age. Impaired osteoblast formation was temporally associated with decreased bone formation and decreased bone mineral density, as determined by histomorphometric analysis of tetracycline-labeled cancellous bone and dual-energy x-ray absorptiometry, respectively. Osteoclastogenesis determined in ex vivo bone marrow cultures was also decreased in these mice, as was the number of osteoclasts in histologic sections. Moreover, unlike controls, senescence-accelerated mice failed to increase osteoclast development after gonadectomy. The osteoclastogenesis defeat was secondary to impaired osteoblast formation as evidenced by the fact that osteoclastogenesis could be restored by addition of osteoblastic cells from normal mice. These findings provide the first demonstration of a link between low bone mineral density and decreased osteoblastogenesis in the bone marrow and validate the senescence-accelerated mouse as a model of involutional osteopenia.

Aging↗
PubMed1995

Bone marrow, cytokines, and bone remodeling. Emerging insights into the pathophysiology of osteoporosis.

Both osteoblasts and osteoclasts are derived from progenitors that reside in the bone marrow; osteoblasts belong to the mesenchymal lineage of the marrow stroma, and osteoclasts to the hematopoietic lineage. The development of osteoclasts from their progenitors is dependent on stromal-osteoblastic cells, which are a major source of cytokines that are critical in osteoclastogenesis, such as interleukin-6 and interleukin-11. The production of interleukin-6 by stromal osteoblastic cells, as well as the responsiveness of bone marrow cells to cytokines such as interleukin-6 and interleukin-11, is regulated by sex steroids. When gonadal function is lost, the formation of osteoclasts as well as osteoblasts increases in the marrow, both changes apparently mediated by an increase in the production of interleukin-6 and perhaps by an increase in the responsiveness of bone marrow progenitor cells not only to interleukin-6 but also to other cytokines with osteoclastogenic and osteoblastogenic properties. The cellular activity of the bone marrow is also altered by the process of aging. Specifically, senescence may decrease the ability of the marrow to form osteoblast precursors. The association between the dysregulation of osteoclast or osteoblast development in the marrow and the disruption of the balance between bone resorption and bone formation, resulting in the loss of bone, leads to the following notion. Like homeostasis of other regenerating tissues, homeostasis of bone depends on the orderly replenishment of its cellular constituents. Excessive osteoclastogenesis and inadequate osteoblastogenesis are responsible for the mismatch between the formation and resorption of bone in postmenopausal and age-related osteopenia. The recognition that changes in the numbers of bone cells, rather than changes in the activity of individual cells, form the pathogenetic basis of osteoporosis is a major advance in understanding the mechanism of this disease.

Animals↗
PubMed1995

Sex steroids, cytokines and the bone marrow: new concepts on the pathogenesis of osteoporosis.

Osteoclasts and osteoblasts, originating in the bone marrow from haemopoietic progenitors and mesenchymal stromal cells, respectively, are responsible for the remodelling of the skeleton throughout adult life. Upon loss of sex steroids, the production of osteoclasts in the bone marrow is increased. This is mediated by an increase in the production of interleukin 6 (IL-6), as well as an increase in the sensitivity of the osteoclastic precursors to the action of cytokines such as IL-6, owing to an up-regulation of the gp130 signal transduction pathway. Consistent with this, oestrogens as well as androgens inhibit IL-6 production through an indirect effect of their specific receptors on the transcriptional activity of the IL-6 gene promoter, and inhibit the expression of the gp130 gene. With advancing age, the ability of the marrow to maintain the high rate of osteoclastogenesis caused by the acute loss of sex steroids is diminished. This is probably the result of the negative effect of senescence on the ability of the marrow to produce stromal/osteoblastic cells, which provide the essential support for osteoclastogenesis. These observations suggest that inappropriate production of osteoclasts or inadequate production of osteoblasts in the bone marrow are fundamental cellular changes in the pathogenesis of postmenopausal and senescence-associated osteoporosis, respectively.

Adult↗
PubMed1995

New insights into the cellular, biochemical, and molecular basis of postmenopausal and senile osteoporosis: roles of IL-6 and gp130.

It is well established that osteoclasts, the cells responsible for bone resorption, are derived from hematopoietic progenitors (CFU-GM), whereas the bone-forming osteoblasts are of the same lineage as the mesenchymal stromal cells of the bone marrow. Moreover, it is widely accepted that osteoclast formation depends on cells of the stromal/osteoblastic lineage. The appreciation of the ontogeny of osteoclasts and osteoblasts, the interaction between them, and the role of local factors that regulate their development has led to the emergence of new insights into the pathophysiology of the osteopenias associated with estrogen deficiency and senescence. Consistent with histomorphometric data from humans, there is now evidence from studies in animal models suggesting that a critical cellular change caused by the loss of ovarian, as well as testicular, function is an increase in osteoclastogenesis. This change is apparently mediated by an increase in the production of the osteoclastogenic cytokine interleukin-6 by cells of the bone marrow, which follows the removal of an inhibiting control of estrogens or androgens on IL-6. The inhibiting effect of sex steroids on IL-6 production is mediated by their respective receptors and is exerted indirectly on the transcriptional activity of the proximal 225 bp sequence of the IL-6 gene promoter. Besides its effects on IL-6 production, loss of gonadal function may also cause an increase in the sensitivity of the osteoclastic precursors to the action of cytokines such as IL-6, due to an upregulation of the gp130 signal transduction pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Regulation of interleukin-6, osteoclastogenesis, and bone mass by androgens. The role of the androgen receptor.

Interleukin-6 is an essential mediator of the bone loss caused by loss of estrogens. Because loss of androgens also causes bone loss, we have examined whether the IL-6 gene is regulated by androgens, and whether IL-6 plays a role in the bone loss caused by androgen deficiency. Both testosterone and dihydrotestosterone inhibited IL-6 production by murine bone marrow-derived stromal cells. In addition, testosterone, dihydrotestosterone, and adrenal androgens inhibited the expression of a chloramphenicol acetyl transferase reporter plasmid driven by the human IL-6 promoter in HeLa cells cotransfected with an androgen receptor expression plasmid; however, these steroids were ineffective when the cells were cotransfected with an estrogen receptor expression plasmid. In accordance with the in vitro findings, orchidectomy in mice caused an increase in the replication of osteoclast progenitors in the bone marrow which could be prevented by androgen replacement or administration of an IL-6 neutralizing antibody. Moreover, bone histomorphometric analysis of trabecular bone revealed that, in contrast to IL-6 sufficient mice which exhibited increased osteoclast numbers and bone loss following orchidectomy, IL-6 deficient mice (generated by targeted gene disruption) did not. This evidence demonstrates that male sex steroids, acting through the androgen-specific receptor, inhibit the expression of the IL-6 gene; and that IL-6 mediates the upregulation of osteoclastogenesis and therefore the bone loss caused by androgen deficiency, as it does in estrogen deficiency.

Animals↗
PubMed1995

Estrogen loss upregulates hematopoiesis in the mouse: a mediating role of IL-6.

We have previously demonstrated that ovariectomy causes an increase in the number of colony-forming unit granulocyte/macrophage (CFU-GM) and an upregulation of osteoclastogenesis in mice, both of which are mediated by interleukin-6 (IL-6). IL-6 is involved in the development of several hematopoietic progenitors, including the burst-forming unit-erythroid (BFU-E) and multipotent CFUs (CFU-GEMM). Therefore, we performed studies to examine if other hematopoietic progenitors, besides CFU-GM and their progeny, are affected by estrogen loss. We found that ovariectomy caused an increase in the number of CFU-GEMM and BFU-E, as well as an increase of CFU-GM in marrow cells of the femur. Administration of 17 beta-estradiol or a neutralizing antibody against IL-6 prevented the ovariectomy-induced increase in the number of these progenitors in the marrow. Ovariectomy also caused an increase in the number of circulating lymphocytes, neutrophils, and monocytes, which were suppressed by administration of 17 beta-estradiol or the neutralizing antibody against IL-6; however, the number of circulating platelets was unaffected by loss of ovarian function. These data establish that, in addition to upregulation of osteoclastogenesis, loss of estrogens in the mouse causes widespread effects on hematopoiesis, which are apparently mediated by IL-6.

Animals↗
PubMed1994

Endogenous production of tumor necrosis factor by primary cultures of murine calvarial cells: influence on IL-6 production and osteoclast development.

We have previously shown that tumor necrosis factor (TNF) and interleukin-1 (IL-1) acted synergistically to stimulate the production of IL-6 by bone marrow stromal and osteoblastic cells; and that an antibody to IL-6 inhibited TNF-induced osteoclast development in murine calvarial cell cultures. Prompted by this evidence, we have now examined whether TNF and/or IL-1 are produced by murine calvarial cells, and whether these cytokines are involved in IL-6 production and osteoclast formation. When cultured under basal conditions, calvarial cells produced TNF and IL-6, and were able to form bone resorbing osteoclasts. A neutralizing antibody against TNF suppressed both basal IL-6 production and the formation of bone resorbing osteoclasts. The anti-TNF antibody also inhibited IL-6 production in response to exogenous IL-1 or parathyroid hormone (PTH). In contrast, a neutralizing anti-IL-1 receptor antibody had no effect on basal, TNF- or PTH-stimulated IL-6 production. These findings suggest that TNF, but not IL-1, is produced by murine bone cells and that endogenous TNF induces the IL-6 production, osteoclast formation, and bone resorption exhibited by these cultures under basal conditions. Furthermore, bone cell-derived TNF amplifies the stimulatory effect of exogenous IL-1 or PTH on IL-6 production by calvarial cells.

Animals↗
PubMed1994

Interleukin-11: a new cytokine critical for osteoclast development.

Stromal cells of the bone marrow control the development of osteoclasts through the production of cytokines capable of promoting the proliferation and differentiation of hematopoietic progenitors. Moreover, the deregulated production of the cytokine IL-6 in the bone marrow mediates an increase in osteoclastogenesis after estrogen loss. IL-6, however, does not influence osteoclastogenesis in the estrogen-replete state, suggesting that other cytokines might be responsible for osteoclast development under physiologic circumstances. We report here that IL-11, a newly discovered cytokine that is produced by marrow stromal cells, induced the formation of osteoclasts exhibiting an unusually high degree of ploidy in cocultures of murine bone marrow and calvarial cells. Osteoclasts formed in the presence of IL-11 were capable of bone resorption, as evidenced by the formation of resorption pits, as well as the release of 45Ca from prelabeled murine calvaria. Further, an antibody neutralizing IL-11 suppressed osteoclast development induced by either 1,25-dihydroxyvitamin D3, parathyroid hormone, interleukin-1, or tumor necrosis factor; whereas inhibitors of IL-1 or TNF had no effect on IL-11-stimulated osteoclast formation. The effects of IL-11 on osteoclast development were blocked by indomethacin; more important, however, they were independent of the estrogen status of the marrow donors.

Animals↗
PubMed1993

Demonstration of estrogen and vitamin D receptors in bone marrow-derived stromal cells: up-regulation of the estrogen receptor by 1,25-dihydroxyvitamin-D3.

We have shown earlier that 17 beta-estradiol inhibits cytokine-induced interleukin-6 (IL-6) production by bone marrow-derived stromal cells as well as osteoblasts, two types of cells with a critical influence on osteoclast development, and that ovariectomy causes an IL-6-mediated up-regulation of osteoclastogenesis in mice. Prompted by this, we have searched here for the presence of estrogen receptors (ERs) in two murine bone marrow-derived stromal cell lines, +/+ LDA11 and MBA 13.2, and the osteoblast-like cell line MC3T3-E1. All three cell lines exhibited high affinity saturable binding for [125I]17 beta-estradiol with a dissociation constant of approximately 10(-10) M and concentration of binding sites of 260 +/- 30, 170 +/- 10, and 90 +/- 10 sites per cell, respectively. In addition, we amplified complementary DNA from the stromal cell lines by polymerase chain reaction using oligonucleotide primers flanking the DNA binding domain of the murine uterine ER. The amplified product showed an identical nucleotide sequence to the DNA binding domain of the murine uterine receptor. Consistent with the functionality of the ER in stromal cells, and specifically its role in the regulation of IL-6 by 17 beta-estradiol, we found that the pure estrogen antagonist ICI 164,384 completely prevented the effect of 17 beta-estradiol on IL-6. All three cell lines also expressed receptors for 1,25-dihydroxyvitamin-D3 [1,25(OH)2D3] (dissociation constant, approximately 10(-10) M), with a concentration of binding sites of 490 +/- 20, 920 +/- 20, and 1110 +/- 70 sites per cell, respectively. 1,25(OH)2D3 treatment of the stromal cells caused a 2-fold increase in the concentration of ERs and a decrease in cell proliferation. These data establish that bone marrow-derived stromal cells express functional estrogen as well as vitamin D receptors, which serve to mediate actions of their respective ligands on the biosynthetic activity of these cells and presumably the effects of these two steroid hormones on osteoclastogenesis.

Animals↗
PubMed1993

Increased interleukin-6 production by murine bone marrow and bone cells after estrogen withdrawal.

We have previously shown that cytokine-induced production of interleukin-6 (IL-6) by cultured bone marrow-derived stromal and osteoblastic cells is inhibited by 17 beta-estradiol, and that estrogen withdrawal (ovariectomy) in mice causes an up-regulation of osteoclast development which can be prevented by a neutralizing antibody against IL-6 or estrogen replacement. To directly establish the link between estrogen loss and altered IL-6 production, implied by our earlier studies, we have now compared IL-6 production in ex vivo cultures of bone marrow cells from mice that were sham operated, ovariectomized, or ovariectomized and treated with 17 beta-estradiol. In addition, we have examined the effect of the in vitro withdrawal of estrogens from primary cell cultures of neonatal murine calvaria on IL-6 production. IL-6 production in ex vivo cultures of bone marrow cells maintained in the presence of 1,25-dihydroxyvitamin D3 or PTH was greater in marrow cells from ovariectomized mice than in those from sham-operated animals or ovariectomized animals receiving estrogen replacement. In line with this finding, addition of 17 beta-estradiol to calvaria cell cultures followed by withdrawal of the steroid caused an increase in the amount of IL-6 produced in response to the subsequent stimulation of these cultures with IL-1 or PTH compared to that in cultures that had never been treated with estradiol; when the inactive isomer 17 alpha-estradiol was used, no change in IL-6 production was observed. These results establish that estrogen loss causes an up-regulation of IL-6 production by bone marrow cells and that a similar phenomenon can be elicited in vitro by withdrawal of 17 beta-estradiol from primary cultures of bone cells.

Animals↗
PubMed1992

Increased osteoclast development after estrogen loss: mediation by interleukin-6.

Osteoclasts, the cells that resorb bone, develop from hematopoietic precursors of the bone marrow under the control of factors produced in their microenvironment. The cytokine interleukin-6 can promote hematopoiesis and osteoclastogenesis. Interleukin-6 production by bone and marrow stromal cells is suppressed by 17 beta-estradiol in vitro. In mice, estrogen loss (ovariectomy) increased the number of colony-forming units for granulocytes and macrophages, enhanced osteoclast development in ex vivo cultures of marrow, and increased the number of osteoclasts in trabecular bone. These changes were prevented by 17 beta-estradiol or an antibody to interleukin-6. Thus, estrogen loss results in an interleukin-6-mediated stimulation of osteoclastogenesis, which suggests a mechanism for the increased bone resorption in postmenopausal osteoporosis.

Analysis of Variance↗
PubMed1992

17 beta-estradiol inhibits interleukin-6 production by bone marrow-derived stromal cells and osteoblasts in vitro: a potential mechanism for the antiosteoporotic effect of estrogens.

The effect of 17 beta-estradiol on interleukin-6 (IL-6) synthesis was examined in murine bone marrow-derived stromal cell lines, normal human bone-derived cells, and nontransformed osteoblast cell lines from mice and rats. In all these cell types IL-6 production was stimulated as much as 10,000-fold in response to the combination of recombinant interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha). Addition of 17 beta-estradiol in the cultures exerted a dose-dependent inhibition of IL-1-, TNF-, and IL-1 + TNF-induced production of bioassayable IL-6. Testosterone and progesterone (but not 17 alpha-estradiol) also inhibited IL-6, but their effective concentrations were two orders of magnitude higher than 17 beta-estradiol. 17 beta-estradiol also decreased the levels of the IL-6 mRNA. In addition, estradiol inhibited both TNF-induced IL-6 production and osteoclast development in primary bone cell cultures derived from neonatal murine calvaria. The TNF-stimulated osteoclast development was also suppressed by a neutralizing monoclonal anti-IL-6 antibody. This in vitro evidence suggests, for the first time, a mechanistic paradigm by which estrogens might exert at least part of their antiresorptive influence on the skeleton.

Animals↗
PubMed1990

Comparison of bone and parathyroid hormone as stimulators of osteoclast development and activity in calvarial cell cultures from normal and osteopetrotic (mi/mi) mice.

Osteoclast development was studied in cell cultures prepared from calvaria of neonatal osteopetrotic (mi/mi) mice or their normal littermates, using tartrate-resistant acid phosphatase (TRAPase), as an osteoclast marker. In cultures from normal mice, treatment with 10 nM PTH for 4-5 days stimulated the formation of osteoclasts. However in cultures from mi/mi mice, this response was only 7% +/- 5% that of normal mice and they were significantly smaller than osteoclasts of normal mice. Mineralized bone particles elicited osteoclast development in cultures from both normal and mi/mi mice, and osteoclast size was identical for both genotypes. Seventy-eight to 96% of the TRAPase-positive cells bound 125I-CT, as demonstrated by autoradiography. 125I-CT binding characteristics were identical in cultures from both genotypes treated with bone particles, exhibiting a Kd of 3.3-3.6 x 10(-10) M. Addition of PTH stimulated 45Ca release from the added bone particles only in the case of cultures prepared from normal mice, and CT inhibited this response. Cells from normal mice were capable of excavating bone from the surface of smooth cortical bone wafers, but such excavations were rarely seen in the case of calvarial cells from mi/mi mice. Thus, PTH-driven differentiation of osteoclasts is arrested in calvarial cell cultures from mi/mi mice, but mi/mi preosteoclasts retain the ability to express certain osteoclast markers in response to bone derived signals. We hypothesize that the lack of activity of mi/mi osteoclasts is due to the failure of mi/mi preosteoclasts to respond appropriately to resorptive agents, or to cytokines elicited by these agents.

Acid Phosphatase↗
PubMed1990

Impaired gastric acid secretion in mast cell-deficient mice.

Gastric acid secretion in normal (+/+) C57B1/6J mice and congeneic, mast cell-deficient (mi/mi) C57B1/6J mice was examined. The mast cell-deficient animals had approximately 50% of the normal quantity of gastric histamine and a blunted basal acid level and secretory response. These observations were noted despite the presence of parietal cells, which were normal in number and morphology. The H2-antagonist ranitidine inhibited basal acid secretion in both groups of animals. Exogenous histamine induced a significant secretory response in normal and mast cell-deficient groups, but only the secretory response in normal animals could be blocked by the H2-antagonist. Treatment of mast cell-deficient animals with histamine for seven consecutive days before stimulation did not restore the histamine response to the normal (+/+) levels. The normal animals demonstrated an acid secretory response to pentagastrin. Mast cell-deficient mice also responded to pentagastrin, but the response was less than that observed in the normal animals, and a significant difference was not evident in all experiments. Furthermore, simultaneous injection of mast cell-deficient animals with histamine and pentagastrin did not restore pentagastrin responsiveness to normal levels, although the histamine concentration used was sufficient to raise acid secretion to basal levels of normal mice. These results support the conclusion that non-mast cell histamine only partially contributes to basal gastric acid secretion and is insufficient to facilitate full parietal cell responsiveness. Furthermore, pentagastrin requires the presence of mast cells to elicit a maximal secretory response but can use non-mast cell histamine to activate the parietal cells for acid secretion.

Animals↗