Regulation of Cytoplasmic pH in Osteoclasts

Nordström, Tommy; Rotstein, Ori D.; Romanek, R.; Asotra, Satish; Heersche, J. N. M.; Manolson, Morris F.; Brisseau, Guy F.; Grinstein, Sergio

doi:10.1074/jbc.270.5.2203

Cited by 98 publications

(49 citation statements)

References 43 publications

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“…Moreover, in osteoclasts, numerous bafilomycin-insensitive acidic vacuoles (47) and some alternative forms of vacuolar pumps have been reported (16,17). The existence of bafilomycin-insensitive H+ extrusion pathway in osteoclasts was previously reported by us (36a) and others (48).…”

Section: Introductionmentioning

confidence: 56%

Acid extrusion is induced by osteoclast attachment to bone. Inhibition by alendronate and calcitonin.

Zimolo¹,

Wesolowski²,

Rodan³

1995

J. Clin. Invest.

108

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Acid extrusion is essential for osteoclast (OC) activity. We examined Na + and HCO3 --independent H + extrusion in ratand mouse OCs by measuring intracellular pH (pH1) changes, with the pH1 indicator BCECF (biscarboxyethyl-5-(6) carboxyfluorescein) after H+ loading with an ammonium pulse. 90% of OCs attached to glass do not possess HCO3-and Na+-independent H +-extrusion (rate of pH1 recovery = 0.043±0.007 (SEM) pH U/min, n = 26). In contrast, in OCs attached to bone, the pH1 recovery rate is 0.228±0.011 pH. U/min, n = 25. OCs on bone also possess a NH4+-permeable pathway not seen on glass. The boneinduced H+ extrusion was inhibited by salmon calcitonin (10-8 M, for 2 h), and was not present after pretreating the bone slices with the aminobisphosphonate alendronate (ALN). At ALN levels of 0.22 nmol/mm2 bone, H+ extrusion was virtually absent 12 h after cell seeding (0.004±0.002 pH U/min) and 50% inhibition was observed at 0.022 pmol ALN/mm2 bone. The Na+-independent H+ extrusion was not inhibited by bafilomycin Al (up to i-O M), although a bafilomycin Al (10-8 M) -sensitive H+ pump was present in membrane vesicles isolated from these osteoclasts. These findings indicate that Na+-independent acid extrusion is stimulated by osteoclast attachment to bone and is virtually absent when bone is preincubated with ALN, or when osteoclasts are treated with salmon calcitonin. (J. Clin. Invest.

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Section: Introductionmentioning

confidence: 56%

Acid extrusion is induced by osteoclast attachment to bone. Inhibition by alendronate and calcitonin.

Zimolo¹,

Wesolowski²,

Rodan³

1995

J. Clin. Invest.

108

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“…As described earlier (22), rabbit osteoclasts cultured on plastic or glass at physiological pH display a variety of phenotypes; a majority of the cells show a "flat" morphology, with well developed lamellipodia. Migrating osteoclasts displaying the "spread" phenotype can also be observed.…”

Section: Effect Of Extracellular Acidification On Bone Resorption Andmentioning

confidence: 99%

“…By contrast, the plasmalemmal V-ATPase played a relatively minor role (22). To study the effect of extracellular acidosis on proton extrusion mechanisms, osteoclasts plated on glass coverslips were cultured in HEPES-buffered and nominally bicarbonate-free medium at pH 7.5, 7.0, or 6.5.…”

Section: Effect Of Extracellular Acidification On Bone Resorption Andmentioning

confidence: 99%

“…In previous studies, we evaluated the pH regulatory mechanisms in osteoclasts plated on glass coverslips by examining their ability to recover from a cytosolic acid load. pH recovery in these cells was almost completely insensitive to treatment with bafilomycin A 1 , indicating a paucity of V-ATPase activity in the plasma membrane (22). Based on this observation, we reasoned that cultured osteoclasts represent an excellent model for studying the effect of chronic acidosis on plasmalemmal V-ATPase activity.…”

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confidence: 99%

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Chronic Extracellular Acidosis Induces Plasmalemmal Vacuolar Type H+ ATPase Activity in Osteoclasts

Nordström

Shrode

Rotstein

et al. 1997

Journal of Biological Chemistry

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Proton extrusion into an extracellular resorption compartment is an essential component of bone degradation by osteoclasts. Chronic metabolic acidosis is known to induce negative calcium balance and bone loss by stimulating osteoclastic bone resorption, but the underlying mechanism is not known. The present studies were undertaken to evaluate whether chronic acidosis affects proton extrusion mechanisms in osteoclasts cultured on glass coverslips. Acidosis, mimicked experimentally by maintaining the cells at extracellular pH 6.5, rapidly lowered intracellular pH to 6.8. However, after 2 hours, a proportion of cells demonstrated the capacity to restore intracellular pH to near normal levels. To define the mechanism responsible for this recovery, the activity of individual H ؉ transport pathways was analyzed. We found that chronic acid treatment for up to 6 h did not significantly affect the cellular buffering power or Na ؉ /H ؉ antiport activity. In contrast, chronic acidosis activated vacuolar H ؉ pumps in the osteoclasts. Although only ϳ5% of the control cells displayed proton pump activity, about 40% of cells kept at extracellular pH 6.5 for 4 -6 h were able to recover from the acute acid load by means of bafilomycin A 1 -sensitive proton extrusion. Conversely, the H ؉ -selective conductance recently described in the plasma membrane of osteoclasts was clearly inhibited in the cells exposed to chronic acidosis. Following acid treatment, the activation threshold of the H ؉ conductance was shifted to more positive potentials, and the current density was significantly reduced. Considered together, these results suggest that induction of plasmalemmal vacuolar type ATPase activity by chronic acidosis, generated either systemically due to metabolic disease or locally at sites of inflammation, is likely to stimulate osteoclastic bone resorption and thus to promote bone loss.Bone resorption is a multistep process involving migration of osteoclasts and/or osteoclast precursors to the bone surface, attachment to the bone matrix, and subsequent degradation of the underlying bone mineral by local acidification of the osteoclast-bone interface. When resorbing bone, osteoclasts display a specialized attachment zone, called the clear zone, which delimits a sealed compartment characterized by the presence of an extensive ruffled cell membrane (1). Demineralization of the bone matrix requires acidification of this extracellular compartment. Two lines of evidence suggest that the primary cellular mechanism responsible for this acidification is a vacuolar type H ϩ -ATPase (V-ATPase) 1 localized to the ruffled border of these cells. First, immunohistochemical studies demonstrated a marked accumulation of V-ATPases on the ruffled membrane of osteoclasts adherent to bone (2, 3). Second, the bone-resorbing capacity of osteoclasts is effectively inhibited by the specific V-ATPase inhibitor bafilomycin A 1 (4, 5). Considered together, these observations indicate a central role for the plasmalemmal V-ATPase in osteoclastic bone resorptio...

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“…An example of how preserving intracellular pH is protective for the apoptotic cell death pathway is found in hematopoietic stem cells where granulocyte-macrophage colony stimulating factor (GM-CSF) delays apoptosis by cytoplasmic alkalinization through activation of the Na ϩ /H ϩ exchanger and in neutrophils where granulocyte colony stimulating factor (G-CSF) delays apoptosis by activation of the vacuolar proton ATPase (VPATPase) (15)(16)(17). The VPATPase is known to be activated by PKC (15,18,19), suggesting it could be activated during preconditioning.…”

Section: Introductionmentioning

confidence: 99%

Preconditioning rabbit cardiomyocytes: role of pH, vacuolar proton ATPase, and apoptosis.

Gottlieb

Gruol²,

Zhu³

et al. 1996

J. Clin. Invest.

210

107

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Ischemic preconditioning signals through protein kinase C (PKC) to protect against myocardial infarction. This protection is characterized by diminished intracellular acidification. Acidification is also a feature of apoptosis, and several agents act to prevent apoptosis by preventing acidification through activation of ion channels and pumps to promote cytoplasmic alkalinization. We characterized metabolic inhibition, recovery, and preconditioning through a PKC-dependent pathway in cardiomyocytes isolated from adult rabbit hearts. Preconditioning reduced loss of viability assessed by morphology and reduced DNA nicking. Blockade of the vacuolar proton ATPase (VPATPase) prevented the effect of preconditioning to reduce metabolic inhibition-induced acidosis, loss of viability, and DNA nicking. The beneficial effect of Na ϩ /H ϩ exchange inhibition, which is thought to be effective through reduced intracellular Na ϩ and Ca ϩϩ , was also abrogated by VPATPase blockade, suggesting that acidification even in the absence of Na ϩ /H ϩ exchange may lead to cell death. We conclude that a target of PKC in mediating preconditioning is activation of the VPATPase with resultant attenuation of intracellular acidification during metabolic inhibition. Inhibition of the "death protease," interleukin-1-beta converting enzyme or related enzymes, also protected against the injury that followed metabolic inhibition. This observation, coupled with the detection of DNA nicking in cells subjected to metabolic inhibition, suggests that apoptotic cell death may be preventable in this model of ischemia/reperfusion injury. ( J. Clin. Invest. 1996. 97:2391-2398.)

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Regulation of Cytoplasmic pH in Osteoclasts

Cited by 98 publications

References 43 publications

Acid extrusion is induced by osteoclast attachment to bone. Inhibition by alendronate and calcitonin.

Acid extrusion is induced by osteoclast attachment to bone. Inhibition by alendronate and calcitonin.

Chronic Extracellular Acidosis Induces Plasmalemmal Vacuolar Type H+ ATPase Activity in Osteoclasts

Preconditioning rabbit cardiomyocytes: role of pH, vacuolar proton ATPase, and apoptosis.

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