Bone as an ion exchange system: evidence for a link between mechanotransduction and metabolic needs

Abstract

Bone as an ion exchange system: evidence for a link between mechanotransduction and metabolic needs. Am J Physiol Endocrinol Metab 282: E851-E864, 2002. First published November 20, 2001 10.1152/ajpendo.00367.2001.-To detect whether the mutual interaction occurring between the osteocytes-bone lining cells system (OBLCS) and the bone extracellular fluid (BECF) is affected by load through a modification of the BECF-extracellular fluid (ECF; systemic extracellular fluid) gradient, mice metatarsal bones immersed in ECF were subjected ex vivo to a 2-min cyclic axial load of different amplitudes and frequencies. The electric (ionic) currents at the bone surface were measured by a vibrating probe after having exposed BECF to ECF through a transcortical hole. The application of different loads and different frequencies increased the ionic current in a dosedependent manner. The postload current density subsequently decayed following an exponential pattern. Postload increment's amplitude and decay were dependent on bone viability. Dummy and static loads did not induce current density modifications. Because BECF is perturbed by loading, it is conceivable that OBLCS tends to restore BECF preload conditions by controlling ion fluxes at the boneplasma interface to fulfill metabolic needs. Because the electric current reflects the integrated activity of OBLCS, its evaluation in transgenic mice engineered to possess genetic lesions in channels or matrix constituents could be helpful in the characterization of the mechanical and metabolic functions of bone.osteocytes; bone lining cells; mineral homeostasis; mechanical loading; fluid shear stress THE MUTUAL INTERACTION occurring between the osteocyte-bone lining cell system (OBLCS) and the surrounding bone extracellular fluid (BECF) has been suggested to play a pivotal role in bone mechanotransduction (3, 37). OBLCS is constituted by a network of stellate cells buried within the bone matrix, the osteocytes, having an asymmetrical arborization of dendrites polarized toward the bone surfaces, where they come into contact with the bone lining cells or the osteoblasts according to whether the bone is in a resting or a growing phase, respectively. Because the cells forming such a three-dimensional protoplasmic network are all joined by gap junctions, OBLCS actually constitutes a functional syncytium (24,27,26). The lacuno and canalicular network of cavities, enclosing the osteocyte cell bodies and dendrites, forms within the bone matrix a complex microstructure of pores and channels filled by BECF that has a different ionic composition from the systemic extracellular fluid (ECF) of the perivascular loose connective tissue surrounding the bone surfaces.This ionic difference is maintained by a pump-leak system that selectively operates at the OBLCS level (32, 33, 34) as a partition system (4) generating an ionic gradient between BECF and ECF (21, 22, 23, 30) with a subsequent electric potential difference at the bone membrane (36) that appears to be under parathyroid hormone control (2...

In vivo leptin expression in cartilage and bone cells of growing rats and adult humans

“…Because such adipocytes are close to marrow stromal cells and to the other cells of the osteogenic lineage, we agree with the hypothesis suggested by other authors that adipocytederived leptin, in addition to its well-established endocrine role, could serve as a paracrine factor in modulating the activity of the osteogenic cells and the differentiation of haematopoietic precursor cells (Bennet et al 1996;Gainsford et al 1996). In vitro findings on leptin expression appear to be contradictory: according to Ducy et al (2000) rat osteoblasts are leptin negative, whereas according to Reseland et al (2001) connect all these cells, they have been considered a functional syncytium, along which mechanical and metabolic signals can be issued by wiring and volume transmission (Marotti, 1996(Marotti, , 2000Palazzini et al 1998;Palumbo et al 2001;Rubinacci et al 2002). Note that, We are aware that the leptin effect, not only on bone metabolism but also over a larger extent, remains controversial, notwithstanding the huge amount of data recorded.…”

Spatial Distribution of Osteocyte Lacunae in Equine Radii and Third Metacarpals: Considerations for Cellular Communication, Microdamage Detection and Metabolism

“…Despite the ideal location of osteocytes to sense the local environment, their functions, and the relative importance of these functions, remain controversial. The multifactorial functions of osteocytes and the lacunocanalicular spaces in which they reside may include (1) mineral homeostasis [Aarden et al, 1994;Mullender et al, 1996b;Ehrlich et al, 2002;Parfi tt, 2003;Tazawa et al, 2004], (2) nutrient transport and signal transmission [Starkebaum, 1979;Kelly, 1983;Lanyon, 1993;Marotti, 2000;Yellowley et al, 2000;Alford et al, 2003;Mishra and Knothe Tate, 2003], (3) mechanosensation/mechanotransduction [Cowin et al, 1991;Duncan and Turner, 1995;Mosley and Lanyon, 1998;Burger and Klein-Nulend, 1999;Weinbaum et al, 2001;Rubinacci et al, 2002], (4) microdamage detection [Mori and Burr, 1993;Bentolila et al, 1998;Martin, 2000;Reilly, 2000;Vashishth et al, 2000;Noble et al, 2003], and (5) the control of processes that mediate some bone remodeling and modeling activities, as well as the attainment of bone mass [Carter, 1987;Butler, 1989;Mullender and Huiskes, 1995;Terai et al, 1999;Martin, 2000;Power et al, 2002;Vashishth et al, 2002;Burger et al, 2003]. These interrelated functions may be mediated by intercellular communication via gap junctions or cellular activation resulting from interstitial fl uid fl ow.…”

Developmental Bone Biology

“…Length: width = 1.1 14 15 Apical ectodermal ridge 14-17 [15][16][17][18] Hand plate/foot plate 15 16 Mesenchymal skeleton 15 16 Mesenchymal scapula/hip 16 15-18 Mesenchymal humerus, radius, ulna/femur, tibia, fibula 16 17 Chondrifying humerus/femur 16-17 17-18 Chondrifying radius/tibia 17 [17][18] Chondrifying ulna/fibula 17-18 [17][18] Finger rays/toe rays 17-18 18 Chondrifying metacarpus/metatarsus…”