Morphological evidence of reduced bone resorption in osteopetrotic (op) mice

Abstract

Osteopetrosis, a metabolic bone disease in which a generalized accumulation of bone mass reduces or obliterates marrow cavities, is inherited as an autosomal recessive in several mammalian species. A recently discovered mutation in mice, the osteopetrosic (op) mutation, exhibits an elevation in bone matrix synthesis and a resistance to the hypercalcemic effects of exogenous parathyroid extract when young mutants are compared with normal littermates. This investigation examined the number, cytology, and ultrastructure of osteoclasts and the structure of bone surfaces in op mice in a morphologic assessment of bone resorption. Compared with normal littermates, op mice have a severe deficiency of osteoclasts, which also contain unusual toluidine blue-positive and electron-dense cytoplasmic inclusions and hypertrophy of clear zones and ruffled borders. Marrow spaces in op mice contained large numbers of megakaryocytes and large lipoid masses. Bone surfaces exhibiting evidence of resorption by scanning electron microscopy in normal littermates showed no evidence of resorption in op mice. Instead, these areas were characterized by morphologic features of bone formation. These data offer morphologic evidence of a reduction of bone resorption in this mutation. They are interpreted to mean 1) that op mice have a severe reduction in numbers or proliferative capacity of osteoclast precursors, which may be related to the cellular inclusions in the osteoclast population, and 2) that hypertrophy of the ruffled borders and clear zones of op osteoclasts is a compensatory attempt to increase bone resorption.

Carbonic anhydrase II deficiency identified as the primary defect in the autosomal recessive syndrome of osteopetrosis with renal tubular acidosis and cerebral calcification.

“…It has been called "marble bone disease" because the bones are very dense radiographically, although the bones typically have an increased susceptibility to fracture (2,3). Multiple genetic defects produce osteopetrosis but the mechanism common to all the known forms of osteopetrosis is a failure of bone resorption (4). In man, two principal types of osteopetrosis have been described.…”

<b>Histochemical assessment for osteoblastic activity coupled with dysfunctional osteoclasts in </b><i><b>c-src</b></i><b> deficient </b><b>mice </b>

“…We have previously reported that cell coupling with osteoclasts in vivo is necessary for preosteoblastic differentiation into mature osteoblasts to deposit new bone in response to parathyroid hormone (21). Consistently, op/op mice, an- other mouse model lacking osteoclasts (9,18,19,22) revealed the extremely-reduced osteoblastic activity in long bones (26), and defective bone mineralization (30). Taken together, the presence of osteoclasts is important for cell coupling to activate osteoblastic cells in bone remodeling sites in vivo.…”

The role of phosphoinositide 3-kinase in spreading osteoclasts induced by colony-stimulating factor-1

“…The nuclei were partially 5 cm diameter, labeled with [ 32 P]PO 4 32 , and after stimulation with^3 nM CSF-1, the product of the enzyme reaction was extracted. In detail, the osteoblasts were removed, the osteoclast-like cells washed with phosphate-free Hanks solution and subsequently air-incubated in PO 4 32 -free MEM containing Hanks salts, 5 mM HEPES, pH 7.3, and 10% FBS at 37 8C for 1 h. The FBS had been dialyzed against isotonic NaCl and once against phosphate-free medium. For labeling, the cells were air-incubated in 1.5 ml of the same medium containing 75 mCi [ 32 P]PO 4 32 for 1 h. After incubation in PBS with wortmannin or DMSO (DMSO had no effect) for 10 min, the cells were stimulated for various time periods in medium containing^CSF-1 and 10% heat inactivated FBS.…”

“…Homozygous op/op mice are deficient in the synthesis of biologically active cytokines (3). The op phenotype is characterized by a low number of macrophages and osteoclasts (4), the latter causing the impaired bone resorption that leads to osteopetrosis. Daily injection of CSF-1 into op/op mice induced the formation of osteoclasts and reversed the osteopetrotic phenotype, providing conclusive evidence that the development of osteoclasts depends on this cytokine (5).…”