Luun ja dentiinin ORGAANINEN
FAASI ( 30 % luusta)
KOLLAGEENI
( 90 % orgaanisista komponenteista)
Kollageeneja on iso
perhe, 38 geenia koodaa näitä multimeerisiä proteiineja tuottaen
20 erilaista kypsää kollageenia.Päätyyppi kollageenia
kovissa mineralisoituvissa kudoksissa on kollageeni I. Se
muodostuu
kolmoishelixrakenteella kahdella alfa1- ja yhdellä alfa2-ketjulla.
Tämä modifioituu posttranslationaalisesti fosforylaatioilla,
hydroksylaatioilla ja sulfaatioilla, jolloin kolmoisrakenne edelleen
monimutkaistuu. Polymeeri erittyy prekursorinaan peptidiulokkeet
molemmissa päissään ( N- ja C-terminaaleissaan).
Kaikkien ketjujen tulee
olla aivan tarkasti järjestyksessä. Siksi yhdenkin ketjun
mutaatiolla on kauaskantoiset seuraukset luukudokseen. Kollageenityypin I mutaatiot johtavat heterogeeniseen puutteelliseen luutumiseen,
osteogenesis imperfecta,”brittle bone disease”. Koska
kollageenin tulee toimia mineraalien saostumisessa alustana, template,
on arveltu eräiden osteoporoosimuotojen taustana myös piilevän
kollageeni-I.ketjun geenien rakenteellisen mutaation.
Heti
solun ulkopuolella kollageenin tripletti modifioituu, kovalentteja
sidoksia muodostuu, erot kovan ja pehmeän kudoksen välillä tulevat
esiin. Tämä poikkisidosten muodostamiskyky antaa luulle sen
tyypillisen sitkeyden. Kollageenilla on vaikutuksia solufunktioihin,
apoptoosiin, soluproliferaatioon ja differentioitumiseen
monimutkaisen kontrollijärjestelmän kautta Se signaloi
solupinnalta tumaan.
collagen type VI, elastin, tenascin) combined with a multiaxial pattern of insertion suggesting a role more complex than attachment alone would justify.
A proportion permeate the cortex to the endosteum (and beyond), fusing into a CIII-rich osteoid layer (<2 μ thick) encompassing all resting surfaces, and with which they apparently integrate into a PERIOSTEAL-SHARPEY FIBER-ENDOSTEUM (PSE) structural continuum. This intraosseous system behaves in favor of bone loss or gain depending upon extraneous stimuli (i.e., like Frost’s hypothetical “mechanostat”). Thus, the birefringent fibers are sensitive to humoral factors (e.g., estrogen causes retraction, rat femur model), physical activity (e.g., running causes expansion, rat model), aging (e.g., causes fragmentation, pig mandible model), and pathology (e.g., atrophied in osteoporosis, hypertrophied in osteoarthritis, human proximal femur), and with encroaching mineral particles hardening the usually soft parts. In this way the unobtrusive periosteal SF network may regulate bone status, perhaps even contributing to predictable “hotspots” of trabecular disconnection, particularly at sites of tension prone to fatigue, and with the network deteriorating significantly before bone matrix loss.
LÄHDE:
(1) SOMOGYI-GANSS Ester Novel non-collagenous modulators of biomineralization in bone and dentin ( 2004, KI, Stockholm) ISBN 91-7140-101-6
(2) Sharpeyn säikeet ovat kollageeniä. Niistä erikseen artikkeli.
- Front Endocrinol (Lausanne). 2012 Aug 9;3:98. doi: 10.3389/fendo.2012.00098. eCollection 2012. Periosteal Sharpey's fibers: a novel bone matrix regulatory system?
Sharpey's
"perforating" fibers (SF) are well known skeletally in tooth anchorage.
Elsewhere they provide anchorage for the periosteum and are less well
documented.
Immunohistochemistry has transformed their potential significance by identifying their collagen type III (CIII) content and enabling their mapping in domains as permeating arrays of fibers (5-25 μ thick), protected from osteoclastic resorption by their poor mineralization.
As periosteal extensions they are crucial in early skeletal development and central to intramembranous bone healing, providing unique microanatomical avenues for musculoskeletal exchange, their composition (e.g., collagen type VI, elastin, tenascin) combined with a multiaxial pattern of insertion suggesting a role more complex than attachment alone would justify.
A proportion permeate the cortex to the endosteum (and beyond), fusing into a CIII-rich osteoid layer (<2 μ thick) encompassing all resting surfaces, and with which they apparently integrate into a PERIOSTEAL-SHARPEY FIBER-ENDOSTEUM (PSE) structural continuum.
This intraosseous system behaves in favor of bone loss or gain depending upon extraneous stimuli (i.e., like Frost's hypothetical "mechanostat"). Thus, the birefringent fibers are sensitive to humoral factors (e.g., estrogen causes retraction, rat femur model), physical activity (e.g., running causes expansion, rat model), aging (e.g., causes fragmentation, pig mandible model), and pathology (e.g., atrophied in osteoporosis, hypertrophied in osteoarthritis, human proximal femur), and with encroaching mineral particles hardening the usually soft parts. In this way the unobtrusive periosteal SF network may regulate bone status, perhaps even contributing to predictable "hotspots" of trabecular disconnection, particularly at sites of tension prone to fatigue, and with the network deteriorating significantly before bone matrix loss.
Immunohistochemistry has transformed their potential significance by identifying their collagen type III (CIII) content and enabling their mapping in domains as permeating arrays of fibers (5-25 μ thick), protected from osteoclastic resorption by their poor mineralization.
As periosteal extensions they are crucial in early skeletal development and central to intramembranous bone healing, providing unique microanatomical avenues for musculoskeletal exchange, their composition (e.g., collagen type VI, elastin, tenascin) combined with a multiaxial pattern of insertion suggesting a role more complex than attachment alone would justify.
A proportion permeate the cortex to the endosteum (and beyond), fusing into a CIII-rich osteoid layer (<2 μ thick) encompassing all resting surfaces, and with which they apparently integrate into a PERIOSTEAL-SHARPEY FIBER-ENDOSTEUM (PSE) structural continuum.
This intraosseous system behaves in favor of bone loss or gain depending upon extraneous stimuli (i.e., like Frost's hypothetical "mechanostat"). Thus, the birefringent fibers are sensitive to humoral factors (e.g., estrogen causes retraction, rat femur model), physical activity (e.g., running causes expansion, rat model), aging (e.g., causes fragmentation, pig mandible model), and pathology (e.g., atrophied in osteoporosis, hypertrophied in osteoarthritis, human proximal femur), and with encroaching mineral particles hardening the usually soft parts. In this way the unobtrusive periosteal SF network may regulate bone status, perhaps even contributing to predictable "hotspots" of trabecular disconnection, particularly at sites of tension prone to fatigue, and with the network deteriorating significantly before bone matrix loss.
KEYWORDS:
collagen type III; collagen type VI; elastin; endosteal membrane; matrix biochemical domains; skeletal aging; tenascincollagen type VI, elastin, tenascin) combined with a multiaxial pattern of insertion suggesting a role more complex than attachment alone would justify.
A proportion permeate the cortex to the endosteum (and beyond), fusing into a CIII-rich osteoid layer (<2 μ thick) encompassing all resting surfaces, and with which they apparently integrate into a PERIOSTEAL-SHARPEY FIBER-ENDOSTEUM (PSE) structural continuum. This intraosseous system behaves in favor of bone loss or gain depending upon extraneous stimuli (i.e., like Frost’s hypothetical “mechanostat”). Thus, the birefringent fibers are sensitive to humoral factors (e.g., estrogen causes retraction, rat femur model), physical activity (e.g., running causes expansion, rat model), aging (e.g., causes fragmentation, pig mandible model), and pathology (e.g., atrophied in osteoporosis, hypertrophied in osteoarthritis, human proximal femur), and with encroaching mineral particles hardening the usually soft parts. In this way the unobtrusive periosteal SF network may regulate bone status, perhaps even contributing to predictable “hotspots” of trabecular disconnection, particularly at sites of tension prone to fatigue, and with the network deteriorating significantly before bone matrix loss.
Keywords: collagen type III, collagen type VI, tenascin, elastin, matrix biochemical domains, skeletal aging, endosteal membrane
Diagram showing (A)
a stylized CIII/CVI-rich periosteal Sharpey’s fiber with adherent
beaded chains of tenascin and encircled by a coil of elastin, and (B) tracings of the same coarse fibers (about 15 μm diameter) in cross section showing ...
There
now follows seven reasons why the Sharpey’s fiber network may act as an
extracellular regulatory system in bone. Its candidature has been a
lengthy one. Though not assigned as such, elements of the trabecular
framework proposed below probably commenced in the seventeenth century
at the dawn of microscopy with descriptions by Clopton Havers (Dobson, 1952)
of penetrating “fibrillae,” thereby possibly preceding Sharpey himself.
The precise nature of the musculoskeletal exchange mechanism instigated
remains to be established, for example, a piezoelectric phenomenon (the
piezoelectric modulus of tendon is apparently 30-fold that of bone; Marino and Becker, 1971) or one involving stress-regulated excitatory amino acids analogous to neural pathways (Mason et al., 1997)
may be considered; there is also evidence that the ligaments with which
the Sharpey’s fibers integrate may function as proprioceptors (Johansson et al., 1991).
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