Osteogenic Precursor Cells Research Articles

The Role of Bone Marrow in Bone Morphogenetic Protein-induced Repair of Femoral Massive Diaphyseal Defects

The midshaft of the femur of one-year-old rats was resected and the reparative process completely blocked by distraction of the bone ends with an omega-shaped wire. Bone repair extended retrograde instead of across the diaphyseal defect and invariably culminated in nonunion. New bone was induced to grow across the defect by implantation of BMP, and regeneration was similarly enhanced by transplantation of autologous marrow, but union was produced only by composite transplants of marrow and implants of BMP. Union occurred more rapidly from the transplant-implant composite than from autologous cortical bone. These observations suggest that bone marrow stroma cell include both pre-existing osteogenic precursor cells and mesenchymal cells that respond to BMP by differentiating into osteoblast for the repair of large femoral bone defects.

Changes in polyamines, RNA synthesis, and cell proliferation during matrix-induced cartilage, bone, and bone marrow development

Changes in the levels of putrescine, spermidine, and spermine and their biosynthetic enzymes, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAM-decarboxylase) were studied during matrix-induced endochondral bone and bone marrow development. Ribonucleic acid (RNA) synthesis was studied by [ 3H]uridine incorporation into an acid-precipitable fraction. ODC and SAM-decarboxylase activity exhibited similar peaks on Day 3 and on Days 8 and 9 after matrix implantation and were correlated with corresponding peaks of [ 3H]thymidine incorporation during proliferation of chondroprogenitor and osteoprogenitor cells, respectively. In contrast an increase in SAM-decarboxylase but not ODC was observed during hematopoietic bone marrow formation while the incorporation of [ 3H]thymidine in these cells remained high. The concentrations of all three polyamines were low on Day 1 and rose to peak values during osteogenesis on Day 11 and declined thereafter. Putrescine, but not spermidine or spermine, also exhibited an earlier smaller but broad peak on Days 3–7 during mesenchymal cell proliferation and cartilage differentiation. Incorporation of [ 3H]uridine into acid-precipitable material exhibited two peaks on Days 5 and 11 during early phase of chondrogenesis and osteogenesis. The peak levels of putrescine, spermidine, and spermine on Day 11 coincided with increased RNA synthesis during osteogenesis. Autoradiographic localization of [ 3H]thymidine indicated a stimulation of cell proliferation adjacent to matrix particles prior to chondrogenesis and osteogenesis. Osteogenic precursor cells tended to be in close apposition to chondrolytic foci on Day 11.

Cartilage and bone formation in arterial wall. 2. Ultrastructural patterns.

The ultrastructural aspects of cartilaginous and osseous foci developed in aorta of rabbits immunized against rat aorta homogenates was studied. Besides normal and modified smooth muscle cells, various types of transformed mediacytes were observed in and around these foci: some of them resembled connective and young mesenchymatous cells, others had the appearances of cartilaginous and osseous cells. The possible role of the modified (multipotential) smooth muscle cells in aortic chondro- and osteogenesis is considered in some cases. Following histogenetic pathway is suggested: s.m.c. leads to modified s.m.c. lead to young mesenchyme-like cells ("inducible osteogenic precursor cells") leads to "chondro-mediacytes", "osteomediacyte".

Opsonic activity of the serum of germfree guinea pigs contaminated by single strains of the intestinal microflora

A bone marrow fragment transplanted under the kidney capsule created a focus of ectopic hemopoiesis, whose isze, measured by the number of hemopoietic cells, was proportional to the implant size. Dimensions of the focus proved to be 11/2--21/2 greater in the irradiated than in the intact recipients. Cells building up the focus of heterotopic hemopoiesis had a different radiosensitivity in the intact and irradiated recipients--their Do constituted about 160 and 350 rad, respectively. In this connection it is supposed that two cell populations of precursors took part in the creation of the focus. Their possible relations with the determined and inducible osteogenic precursor cells are discussed.

Effects of Radiation on Bone Formation: A Functional Assessment

MORSE, B. S., GIULIANI, D., AND GIULIANI, E. R. Effects of Radiation on Bone Formation: A Functional Assessment. Radiat. Res. 60, 307-313 (1974). A reduction of estrone-induced endosteal bone formation was noted in the tibia of mice locally X-irradiated with doses in excess of 900 R. When estrone injections were started 4 days postirradiation, increased bone formation was noted between 300 and 900 R. As the dose of radiation was increased above 900 R, there was a progressive impairment of the response to estrone injections. Bone formation, though substantially reduced, was still demonstrable after 2220 R. Little recovery was noted over a 7-mo period following this dose. A functional separation of hemopoietic and osteogenic precursor cells was achieved; the former displayed greater radiosensitivity than the latter.

Osteoporotic Mechanisms

Osteogenic cells are derived from sinusoid vessel walls. When conditions are favourable—a supply of energy, correct concentrations of oxygen and carbon dioxide, the hormone balance on the anabolic and anticatabolic side, the osteogenic factor present—osteogenic precursor cells differentiate to osteoblasts and osteocytes. When the balance is on the catabolic side precursor cells coalesce to form osteoclasts. When catabolic conditions persist osteoclastic activity continues until all the precursor cells are used up. Phagocytic cells can also enlarge and coalesce to form osteoclasts. Parathyroid hormone is needed for coalescence. The formation of these osteoclasts is stimulated by an increased marrow pressure or exposure of dead bone tissue. Corticosteroids prevent initial enlargement of cells. Excess parathyroid hormone stimulates the production and activity of extra phagocytic osteoclasts. The hormone balance may approach the catabolic during later stages of pregnancy and after childbirth, after the menopause, during and after the general hormonal decline in old age, when corticosteroids are given for therapeutic purposes, or as a result of the action of contraceptive agents. The effects of stress (caused by the unpleasant emotions, fear, apprehension frustration, jealousy, anxiety, etc, as well as serious illness or trauma) include a rise in blood cortisol levels. A combination of factors may result in corticosteroid levels exceeding the threshold for thrombus formation. This threshold depends on the other chemicals affecting the pituitary-adrenal system that are present. It is abnormally low for contraceptive agents. These mechanisms of bone formation and removal account for the main types of osteoporosis. A lowered blood flow arises from a decrease or cessation of muscle activity, the effect of catabolic compounds on muscle fibres, or thrombi lodged in vessels supplying muscles and bone. A build-up of pressure stimulates the formation of phagocytic osteoclasts, while until the flow is increased again there is insufficient stimulus for new bone formation. When catabolic conditions prevail, osteogenic precursor cells coalesce to osteoclasts, and when anticatabolic conditions return, more precursor cells are formed that may proceed to osteoblast and bone formation before the next catabolic episode. With an unfortunate timing of alternations this results in considerable bone loss. In pregnancy the loss is temporary, but after the menopause and in old age there may be a permanent decrease of bone tissue. This type of osteoporosis may also be caused by contraceptive agents. It leads to backache, the increased number of fractured wrists in older women, and intracapsular hip fractures. Small thrombi cause irreversible osteoporosis. Blood flow through bone is decreased, and vessels in cortical bone blocked. Bone served by these vessels dies, and with prolonged catabolic conditions a considerable amount of dead bone tissue may be present. After phagocytic removal it is not usually replaced. This type of ‘senile’ osteoporosis, which can cause extracapsular hip fractures, is common in old age. It is also the main mechanism of osetoporosis caused by contraceptive agents. There are racial variations. Negroes are the least susceptible and the Japanese the most susceptible. In elderly people senile osteoporosis is part of a more generalized condition. The liver and brain are also affected—there are considerable individual variations, but symptoms often include depression and sometimes pyschotic episodes. Like diabetes and thyroid deficiency, an anticatabolic deficiency requires continuous therapy. The anticatabolic agent chosen should be one that reverses corticosteroid effects on bone, liver and brain efficiently, and at the same time has a high Cortisol threshold for thrombus formation.

Osteogenic precursor cells of bone marrow in radiation chimeras.

A study of the osteogenic and hematopoietic capacities of bone marrow precursor cells was made by transplanting allogeneic marrow and semisyngeneic parental marrow under the renal capsules of F1 hybrid mice. The results indicate that the osteogenic precursor cells (OPC) of semisyngeneic marrow remain active for protracted periods without replenishment by hematopoietic cells. The independence of OPC from hematopoietic cells is confirmed by transplants to lethally irradiated hybrids, since the OPC are capable of self-maintenance in this situation without the possibility of stem cells being provided by the recipient. It is concluded that marrow contains independent lines of OPC and hematopoietic stem cells. Allogeneic marrow is subject to immunological rejection, as is syngeneic male marrow transplanted to presensitized females.

HETEROTOPIC TRANSPLANTS OF BONE MARROW

In semisyngeneic heterotopic bone marrow transplants the donor or recipient origin of cells of osteogenic and hematopoietic tissues was identified by chromosome markers (T6) and by reverse transplantation into the initial donor line. In syngeneic and semisyngeneic grafts of bone marrow under the renal capsule bone and bone marrow are formed. In allogeneic grafts only bone is formed; this bone is subsequently resorbed. In 14-month semisyngeneic transplants the bone marrow consists of recipient cells. This is true for both the proliferating pool and the stem cells of hematopoietic tissue. At the same time, osteogenic precursor cells and bone tissue in these transplants are of donor origin. A discussion is presented of the interrelationship between determinated osteogenic precursor cells (preosteoblasts) and hematopoietic stem cells (or their descendants) in which osteogenesis is inducible.

Localization of Alkaline Phosphatase in the Histogenesis of Cartilage and Bone

1. Meckel's cartilages and the intramembranous sites of ossification in the mandible, tympanic ring, and the anterior process of the malleus of fetal rats between fifteen and twenty days of intrauterine life have been studied with respect to the localization of alkaline phosphatase during the normal differentiation of embryonic mesenchymal cells to osteoblasts and chondroblasts. 2. Alkaline phosphatase appears in the nuclei concurrent with the preliminary condensation of osteogenic mesenchymal cells in the primordium of an intramembranous ossification center. 3. With further differentiation of these osteogenetic precursors to bone-forming cells, the enzynme appears in the nucleoli and in the cytoplasm. At an osteoblastic stage it also appears intercellularly in the osteoid matrix. 4. Mesenchymal cells that have not differentiated in an osteogenetic direction are free of enzymatic activity in contrast to the mesenchymal osteogenic precursor cells. 5. No enzymatic activity was noted during the condensation and differentiation of mesenchymal cells in a chondrocytic direction until hypertrophy of chondrocytes took Place preparatory to ossification. 6. Enzymatic activity was demonstrable in the ossifying anterior portion of Meckel's cartilage but not in its nob-ossifying portion. 7. The preskeletal type of tissue, an internmediate between bone and cartilage, which may also be called secondary or hypertrophic cartilage, occurs in the ramus of the membranous bony mandible. This is a neomorphic product in the differentiation of rapidly proliferating osteogenetic on osteoblastic cells in a site of intramembranous ossification. This is well demonstrated by our studies of alkaline phosphatase activity.