Profiling bone morphogenetic proteins and transforming growth factor-βs by hTGF-β3 pre-treated coral-derived macroporous bioreactors: the power of one

Abstract

To study the expression profile of bone morphogenetic proteins and transforming growth factor-βs (BMPs and TGFβs), coral-derived calcium carbonate-based macroporous bioreactors with limited conversion to hydroxyapatite (7% HA/CC) were pre-loaded with and without 250 μg hTGF-β3 and implanted in the rectus abdominis of 3 non-human primates Papio ursinus euthanized on day 60. To investigate the required dose of hNoggin, a BMPs antagonist that controls the induction of bone formation, 7% HA/CC were pre-loaded with 150 μg hNoggin, with 125 μg hTGF-β3/150 μg hNoggin, with or without 125 μg hTGF-β3 and implanted in the r. abdominis of 3 additional animals euthanized on day 90. Quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) evaluated the expression' profile of BMP-2, BMP-3, BMP-4, BMP-6, BMP-7 and TGF-β1, -β2, and -β3 in tissue generating bioreactors as well as in the adjacent r. abdominis muscle. On day 60, 250 μg hTGF-β3 induced bone formation at the periphery of the implanted bioreactors only. On day 90, 125 μg hTGF-β3/treated bioreactors showed the induction of bone formation throughout the macroporous spaces. Untreated bioreactors induced bone, 4.11% vs. 2.00% on days 60 and 90, respectively. In hTGF-β3/treated bioreactors, BMP-2 and BMP-3 were up-regulated at both time periods, both in the homogenized constructs and in the adjacent r. abdominis muscle whilst BMP-4 in the homogenized construct only. In untreated 7% HA/CC constructs, BMP-2 was up-regulated in the macroporous construct only. On day 60, 250 μg hTGF-β3/treated and untreated macroporous constructs showed up-regulation of TGF-β1 with a six fold increase vs. TGF-β1 expression in adjacent muscle of untreated constructs. TGF-β2 was down regulated in both untreated and 250 μg hTGF-β3/treated bioreactors. On day 60, 250 μg hTGF-β3/treated bioreactors showed TGF-β3 expression in untreated, treated and adjacent muscle tissues. On day 90, BMP-2 was up-regulated, with BMP-3 up-regulation both with and without hNoggin. BMP-4 expression was reduced, with down-regulation of BMP-6 and BMP-7 with and without hNoggin. BMPs expression is finely tuned by hNoggin that blocks BMPs resulting in minimal if any induction of bone formation. The primary differentiating events in untreated bioreactors develop within the macroporous spaces after stem cells invasion and differentiation with lack of BMP-2 expression in the adjacent muscle. In hTGF-β3/treated bioreactors, both the adjacent muscle and the macroporous bioreactor show BMP-2 up-regulation, correlating with the temporo/spatial rapid induction of bone formation at the periphery of the bioreactors only. The latter may be the result of the initiation of a sequential chain of cellular induction rapidly recruiting pericytic perivascular myoblastic cells adjacent to the implanted bioreactors directly transformed into secreting osteoblasts.

Keywords: Bone morphogenetic proteins; Noggin; Primates; The induction of bone formation; Transforming growth factor-β(3); Transforming growth factor-β(s).