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Research: Basic Science Selected Abstracts 2008-2009 |
Hypoxic induction of UCP3 in the growth plate: UCP3 suppresses chondrocyte autophagy.
Watanabe H, Bohensky J, Freeman T, Srinivas V, Shapiro IM.
J Cell Physiol. 2008 Aug;216(2):419-25
The overall goal of the investigation was to examine the role of uncoupling proteins (UCPs) in regulating late stage events in the chondrocyte maturation pathway. We showed for the first time that epiphyseal chondrocytes expressed UCP3. In hypoxia, UCP3 mediated regulation of the mitochondrial transmembrane potential (Δ Ψ m) was dependent on HIF-1 α. We also showed for the first time that UCP3 regulated the induction of autophagy. Thus, suppression of UCP3 enhanced the expression of the autophagic phenotype, even in serum-replete media. Predictably, the mature autophagic chondrocytes were susceptible to an apoptogen challenge. Susceptibility was probably associated with a lowered expression of the anti-apoptotic proteins Bcl2 and BCLxL and a raised baseline expression of cytochrome c in the cytosol. These changes would serve to promote sensitivity to apoptogens. We conclude that in concert with HIF-1 α, UCP3 regulates the activity of the mitochondrion by modulating the transmembrane potential. In addition, it inhibits induction of the autophagic response. When this occurs, it suppresses sensitivity to agents that promote chondrocyte deletion from the growth plate.
SMAD3 functions as a transcriptional repressor of acid-sensing ion channel 3 (ASIC3) in nucleus pulposus cells of the intervertebral disc.
Uchiyama Y, Guttapalli A, Gajghate S, Mochida J, Shapiro IM, Risbud MV.
J Bone Miner Res. 2008 Oct;23(10):1619-28.
The goal of this investigation was to study the regulation of acid-sensing ion channel (ASIC)3 expression by TGFβ in the nucleus pulposus cells of the intervertebral disc. Analysis of human nucleus pulposus tissue indicated decreased ASIC3 and elevated TGFβ expression in the degenerate state. In a parallel study, treatment of nucleus pulposus cells with TGFβ resulted in decreased expression of ASIC3 mRNA and protein. Suppression of ASIC3 promoter activity was evident when the nucleus pulposus cells were treated with TGFβ or co-transfected with the constitutively active ALK5 or a smad3 construct. On the other hand, co-transfection of dominant negative smad3 or smad7 restored ASIC3 promoter activity. We validated the role of smad3 in controlling ASIC3 expression using cells derived from smad3-null mice. ASIC3 promoter activity in the null cells was 2-to 3-fold higher than the wildtype cells. Moreover, expression of smad3 in null cells decreased ASIC3 promoter activity by almost 50%. Further studies using deletion constructs and trichostatin A treatment showed that the full-length smad3 was necessary, and the suppression involved recruitment of histone deacetylase to the promoter. To determine the mechanism, we evaluated the rat ASIC3 promoter sequence and noted the presence of two smad interacting CAGA box motifs. Gel-shift and supershift analysis indicated that smad3 protein was bound to this motif. Chromatin immunoprecipitation analysis confirmed that smad3 bound both the CAGA elements. Results of these studies clearly show that TGFβ is highly expressed in the degenerate disc and through smad3 serves as a negative regulator of ASIC3 expression.
Oxygen tension regulates preosteocyte maturation and mineralization.
Zahm AM, Bucaro MA, Sriniva V, Shapiro IM, Adams CS.
Bone. 2008 Jul;43(1):25-31. Epub 2008 Mar 29.
Oxygen availability is a critical signal for proper development of many tissues, however there is limited knowledge of its role in the maturation of bone cells. To test the hypothesis that low pO2 regulates bone cell mineralization, MLO-A5 and MLO-Y4 cells were cultured in monolayer and three-dimensional alginate scaffolds in hypoxia (2% O2) or normoxia (20% O2). Hypoxia reduced mineralization and decreased alkaline phosphatase activity of preosteocyte-like MLO-A5 cells in both monolayer and alginate cultures. Similar changes in osteogenic activity were seen when the were subjected to chemical hypoxia. Likewise, Osteocytelike MLO-Y4 cells also exhibited reduced osteogenic activity in hypoxia relative to normoxic controls. Based on these observations, it is concluded that a low pO2 decreased the mineralization potential of bone cells at both early and late stages of maturation. Since the oxemic state is transduced by the transcription factor, HIF-1α, experiments were performed to determine if this proteinwas responsible for the observed changes in mineral formation. It was noted that when HIF-1α was silenced, mineralization activities were not restored. Indeed, in hypoxia, in relationship to wild type controls, the mineralization potential of the knockdown cells was further reduced. Based on these findings, it is concluded that the osteogenic activity of preosteocyte-like cells is dependent on both the O2 tension and the expression of HIF-1α.
The inhibition of Staphylococcus epidermidis biofilm formation by vancomycin-modified titanium alloy and implications for the treatment of periprosthetic infection.
Antoci V Jr, Adams CS, Parvizi J, Davidson HM, Composto RJ, Freeman TA, Wickstrom E, Ducheyne P, Jungkind D, Shapiro IM, Hickok NJ.
Biomaterials. 2008 Dec;29(35):4684-90, Epub 2008 Sep 23.
Peri-prosthetic infections are notoriously difficult to treat as the biomaterial implant is ideal for bacterial adhesion and biofilm formation, resulting in decreased antibiotic sensitivity. Previously, we reported that vancomycin covalently attached to a Ti alloy surface (Vanc-Ti) could prevent bacterial colonization. Herein we examine the effect of this Vanc-Ti surface on Staphylococci epidermidis, a Gram-positive organism prevalent in orthopaedic infections. By direct colony counting and fluorescent visualization of live bacteria, S. epidermidis colonization was significantly inhibited on Vanc-Ti implants. In contrast, the gram-negative organism Escherichia coli readily colonized the Vanc-Ti rod, suggesting retention of antibiotic specificity. By histochemical and SEM analysis, Vanc-Ti prevented S. epidermidis biofilm formation, even in the presence of serum. Furthermore, when challenged multiple times with S. epidermidis, Vanc-Ti rods resisted bacterial colonization. Finally, when S. epidermidis was continuously cultured in the presence of Vanc-Ti, the bacteria maintained a Vanc sensitivity equivalent to the parent strain. These findings indicate that antibiotic derivatization of implants can result in a surface that can resist bacterial colonization. This technology holds great promise for the prevention and treatment of periprosthetic infections. |
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