An unanticipated role for sphingosine kinase-2 in bone and in the anabolic effect of parathyroid hormone: Supplementary figures

Sphingosine-1-phosphate (S1P) is an anabolic clastokine. SPHK is the
rate-limiting enzyme in S1P production and has two isoforms. To evaluate
the roles of SPHK1 and SPHK2 in bone, we examined the skeletal phenotype
of mice with selective deletion of SPHK1 in osteoclasts (SPHK1-Oc-/-) and
mice in which the SPHK2 gene was deleted in all tissues (SPHK2-/-).
SPHK1-Oc-/- had normal bone mass. By contrast, SPHK2-/- female mice had a
14% lower spinal BMD (p<0.01) and males a 22% lower BMD at the same
site (p<0.001). SPHK2-/- and control mice were subsequently treated
either with daily PTH(1-34) or vehicle for 29 days. The response to PTH
was significantly attenuated in the SPHK2-/-mice. The mean femoral BV/TV
increased by 24.8% in the PTH-treated female control animals vs 10.6% in
the vehicle-treated female controls (p <0.01). In contrast, in the
SPHK2-/- female mice the difference in femoral trabecular BV/TV at the end
of treatment was not significant (20.5 vs.13.3%, PTH vs. vehicle, p = NS).
The anabolic response to PTH was significantly attenuated in the spine of
male SPHK2-/- mice (29.7% vs. 23.1%, PTH vs. vehicle, in controls, p
<0.05; 26.9% vs. 19.5% PTH vs. vehicle in SPHK2-/- mice, p = NS).
The spine responded normally in the SPHK2-/- female mice. Interestingly,
suppression of Sost was blunted in the SPHK2-/- mice when those animals
were treated with an anabolic PTH regimen. We conclude that SPHK2 has an
important role in mediating both normal bone remodeling and the anabolic
response to PTH.