Carbonic anhydrase II and H + -ATPase in osteoclasts of four osteopetrotic mutations in the rat

Abstract

Osteopetrosis in laboratory animals is a metabolic bone disease characterized by increased skeletal mass. It is inherited as an autosomal recessive and results from a defect in the development and/or function of osteoclasts. We studied two enzymes essential for bone resorption, carbonic anhydrase II isoenzyme (CA II) and H+ -ATPase, in osteoclasts from four osteopetrotic mutations in the rat; namely incisors-absent (ia), osteopetrosis (op), toothless (tl), and microphthalmia (mib), to test the hypothesis that reduced bone resorption in one or more of these mutations results from defects in the synthesis or activity of one of these enzymes. CA II was present in most osteoclasts from normal, tl, op, and mib littermates and was homogeneously distributed in cytoplasm. CA II staining in ia osteoclasts was more variable and less intense than in the other mutations. H+-ATPase was also present in osteoclasts from normal animals and mutants and immunostaining showed clear polarization to the ruffled border region in all normal rats and mutants except ia, which showed diffuse distribution of staining in the cytoplasm. H+-ATPase activity (proton transport) in a related tissue, kidney, was normal in tl and ia rats but increased in op and mib rats compared to their normal littermates. These results suggest that the osteoclasts in osteopetrotic rat mutations are not abnormal with respect to the distribution of CA II and H+ -ATPase and that the function of these enzymes in the skeleton, while likely normal, needs to be tested directly in bone.

Localization of the Mutation Responsible for Osteopetrosis in the op Rat to a 1.5-cM Genetic Interval on Rat Chromosome 10: Identification of Positional Candidate Genes by Radiation Hybrid Mapping

“…Frattini et al (17) have reported that a defect in the T cell immune regulator 1 (TCIRG1) subunit of the vacuolar proton pump is responsible for a subset of human autosomal recessive (malignant) osteopetrosis. However, Sundquist et al (18) have shown that H + ‐ATPase was present in osteoclasts isolated from normal and mutant animals from op stock and that the enzyme was concentrated in the ruffled border region of the cells. Although they were not able to assess the proton pumping ability of osteoclasts, they reported that proton pumping ability in op kidney tissue was elevated when compared with normal littermates (NLMs).…”

Molecular and cellular biology of alveolar bone

“…Diseases that affect bone mass and the normal metabolism of bone can impact on tooth formation and the maintenance of tooth support through the alveolar bone. Thus, defects in genes regulating osteoclast formation and activity often lead to impaired tooth eruption, as observed in op/op mice (265) and core binding factor a1-null mice (122) and in osteopetrotic mutations found in rats (222), such as incisors-absent (ia), osteopetrosis (op), toothless (tl), and microphthalmia (mib). Similarly, defects in tooth development would be expected in osteoprotegerin ligand (123) and nuclear factor kB (65) knockout mice and mice over-expressing osteoprotegerin (212).…”

Rationale for the role of osteoclast‐like cells in arterial calcification

“…Supporting this conclusion are results from mice lacking carbonic anhydrase (CA) II. Osteoclasts lacking CA II are incapable of acidifying the resorptive microenvironment (23,29,30), and mice deficient in CA II are osteopetrotic and develop arterial calcification (31,32). Collectively, findings from these studies suggest that reduced numbers of functional osteoclasts enable mineral deposition by arterial osteoblast-like cells to occur unopposed.…”