Biology Reference
In-Depth Information
(Perez-Amodio et al. 2006a ). Even within a long bone, data indicate site-specific
differences in expression of TRACP (Zenger et al. 2007 ).
8.2.6.5 Resorption Machinery Differs at Different Sites of The Skeleton
As pointed out in some of the previous paragraphs not all osteoclasts are alike.
Osteoclasts at different sites of the skeleton differ with respect to the enzymes used
for resorption (see Everts et al. 1999a , 2006 ; Shorey et al. 2004 ), the level of
TRACP (see Perez-Amodio et al. 2006a ; Zenger et al. 2007 ) and the expression of
the anion exchanger and sodium transporter (Fig. 8.10 ; see (Jansen et al. 2009 )). In
line with the latter finding are data presented by Pham et al. ( 2007 ). These authors
showed that the sodium-proton antiporter NHA2 was highly expressed by osteo-
clasts. The expression proved to be extremely high in the jaw and calvaria but much
lower in the femur. This finding suggests that also for this transporter bone-site
specific differences exist.
In addition, also differences in the size between osteoclasts were noted. Osteo-
clasts present in the calvariae were larger than those present in long bones in bone
biopsies obtained from pycnodysostosis patients (Everts et al. 2003 ). Such differ-
ences in size can be related to the bone resorbing activity of the cells. Ample data
indicate that larger osteoclasts resorb more bone than smaller ones (Lees et al.
2001 ; Lees and Heersche 2000 ). Whether this also counts for the osteoclasts at
different locations of the skeleton has not been investigated yet.
Osteoclast heterogeneity
Skull osteoclast
Slc4a4
AE2
MMP
Cathepsin K
TRACP
Long bone osteoclast
Fig. 8.10 Different bone
sites contain osteoclasts that
differ in various aspects.
Slc4a4 solute carrier 4a4, AE2
anion exchanger 2 [See Everts
et al. ( 2009 ).]
AE2
Cathepsin K
TRACP
Search WWH ::




Custom Search