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- Amirhosseini, Mehdi
(author)
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Aseptic Loosening of Orthopedic Implants : Osteoclastogenesis Regulation and Potential Therapeutics
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Aseptic loosening is the main cause of failure of orthopedic prostheses. With no pharmaceuticals to prevent or mitigate periprosthetic bone degradation, a surgery to replace the loose implant with a new one is the only choice to restore patients’ function. Most studies on mechanisms for aseptic loosening investigate wear debris particle-induced osteolysis. However, pathological loading conditions around unstable implants can also trigger osteoclast differentiation and bone loss.In the first study, global gene expression changes induced by mechanical instability of implants, and by titanium particles were compared in a validated rat model for aseptic loosening. Microarray analysis showed that similar signaling pathways and gene expression patterns are involved in particle- and instability-induced periprosthetic osteolysis with an early onset innate immune response as a hallmark of osteolysis induced by mechanical instability.Further, effects of potential therapeutics on restriction of excessive osteoclast differentiation were evaluated. Wnt signaling pathway is known to regulate bone remodeling. In the second study, effects of inactivation of glycogen synthase kinase 3 beta (GSK-3β), a negative regulator of canonical Wnt signaling, on instability-induced periprosthetic osteolysis were examined using our rat model for aseptic loosening. Inhibition of GSK-3β led to a decrease in osteoclast numbers in the periprosthetic bone tissue exposed to mechanical instability while osteoblast perimeter showed an increase. This was accompanied by higher bone volume fraction (BV/TV) in animals treated with the GSK-3β inhibitor.In the third study, potential beneficial effects of two selective inhibitors of cyclindependent kinase 8/19 (CDK8/19) on bone tissue were evaluated. CDK8/19 is a Mediator complex-associated transcriptional regulator involved in several signaling pathways. CDK8/19 inhibitors, mainly under investigation as treatments for tumors, are reported to enhance osteoblast differentiation and bone formation. We show in this study, for the first time, that inhibition of CDK8/19 led to marked suppression of osteoclast differentiation from bone marrow macrophages in vitro through disruption of the RANK signaling. In mouse primary osteoblasts downregulation of osteopontin mRNA, a negative regulator of mineralization, together with increased alkaline phosphatase activity and calcium deposition indicated that osteoblast mineralization was promoted by CDK8/19 inhibition. Moreover, local administration of a CDK8/19 inhibitor promoted cancellous bone regeneration in a rat model for bone healing.These studies contribute to better understanding of mechanisms behind mechanical instability-induced periprosthetic osteolysis and propose potential therapeutics to restrict bone loss with effects on both osteoclasts and osteoblasts.
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| 2. |
- Amirhosseini, Mehdi, et al.
(author)
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Autoantibodies in outbred Swiss Webster mice following exposure to gold and mercury
- 2021
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In: Toxicology and Applied Pharmacology. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0041-008X .- 1096-0333. ; 412
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Journal article (peer-reviewed)abstract
- Exposure to heavy metals may have toxic effects on several human organs causing morbidity and mortality. Metals may trigger or exacerbate autoimmunity in humans. Inbred mouse strains with certain H-2 haplotypes are susceptible to xenobiotic-induced autoimmunity; and their immune response to metals such as mercury, gold, and silver have been explored. Serum antinuclear antibodies (ANA), polyclonal B-cell activation, hypergammaglobulinemia and tissue immune complex deposition are the main features of metal-induced autoimmunity in inbred mice. However, inbred mouse strains do not represent the genetic heterogeneity in humans. In this study, outbred Swiss Webster (SW) mice exposed to gold or mercury salts showed immune and autoimmune responses. Intramuscular injection of 22.5 mg/kg.bw aurothiomalate (AuTM) induced IgG ANA in SW mice starting after 5 weeks that persisted until week 15 although with a lower intensity. This was accompanied by elevated serum levels of total IgG antibodies against chromatin and total histones. Exposure to gold led to development of serum IgG autoantibodies corresponding to H1 and H2A histones, and dsDNA. Both gold and mercury induced polyclonal B-cell activation. Eight mg/L mercuric chloride (HgCl2) in drinking water, caused IgG antinucleolar antibodies (ANoA) after 5 weeks in SW mice accompanied by immune complex deposition in kidneys and spleen. Serum IgG antibodies corresponding to anti-fibrillarin, and anti-PM/Scl-100 antibodies, were observed in mercury-exposed SW mice. Gold and mercury trigger systemic autoimmune response in genetically heterogeneous outbred SW mice and suggest them as an appropriate model to study xenobiotic-induced autoimmunity.
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| 3. |
- Amirhosseini, Mehdi, et al.
(author)
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Cyclin-dependent kinase 8/19 inhibition suppresses osteoclastogenesis by downregulating RANK and promotes osteoblast mineralization and cancellous bone healing.
- 2019
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In: Journal of Cellular Physiology. - : Wiley. - 0021-9541 .- 1097-4652. ; 234:9, s. 16503-16516
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Journal article (peer-reviewed)abstract
- Cyclin-dependent kinase 8 (CDK8) is a mediator complex-associated transcriptional regulator that acts depending on context and cell type. While primarily under investigation as potential cancer therapeutics, some inhibitors of CDK8-and its paralog CDK19-have been reported to affect the osteoblast lineage and bone formation. This study investigated the effects of two selective CDK8/19 inhibitors on osteoclastogenesis and osteoblasts in vitro, and further evaluated how local treatment with a CDK8/19 inhibitor affects cancellous bone healing in rats. CDK8/19 inhibitors did not alter the proliferation of neither mouse bone marrow-derived macrophages (BMMs) nor primary mouse osteoblasts. Receptor activator of nuclear factor κΒ (NF-κB) ligand (RANKL)-induced osteoclastogenesis from mouse BMMs was suppressed markedly by inhibition of CDK8/19, concomitant with reduced tartrate-resistant acid phosphatase (TRAP) activity and C-terminal telopeptide of type I collagen levels. This was accompanied by downregulation of PU.1, RANK, NF-κB, nuclear factor of activated T-cells 1 (NFATc1), dendritic cell-specific transmembrane protein (DC-STAMP), TRAP, and cathepsin K in RANKL-stimulated BMMs. Downregulating RANK and its downstream signaling in osteoclast precursors enforce CDK8/19 inhibitors as anticatabolic agents to impede excessive osteoclastogenesis. In mouse primary osteoblasts, CDK8/19 inhibition did not affect differentiation but enhanced osteoblast mineralization by promoting alkaline phosphatase activity and downregulating osteopontin, a negative regulator of mineralization. In rat tibiae, a CDK8/19 inhibitor administered locally promoted cancellous bone regeneration. Our data indicate that inhibitors of CDK8/19 have the potential to develop into therapeutics to restrict osteolysis and enhance bone regeneration.
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| 4. |
- Amirhosseini, Mehdi, et al.
(author)
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GSK-3 beta inhibition suppresses instability-induced osteolysis by a dual action on osteoblast and osteoclast differentiation
- 2018
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In: Journal of Cellular Physiology. - : WILEY. - 0021-9541 .- 1097-4652. ; 233:3, s. 2398-2408
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Journal article (peer-reviewed)abstract
- Currently, there are no medications available to treat aseptic loosening of orthopedic implants. Using osteoprotegerin fusion protein (OPG-Fc), we previously blocked instability-induced osteoclast differentiation and peri-prosthetic osteolysis. Wnt/beta-catenin signaling, which regulates OPG secretion from osteoblasts, also modulates the bone tissue response to mechanical loading. We hypothesized that activating Wnt/beta-catenin signaling by inhibiting glycogen synthase kinase-3 beta (GSK-3 beta) would reduce instability-induced bone loss through regulation of both osteoblast and osteoclast differentiation. We examined effects of GSK-3 beta inhibition on regulation of RANKL and OPG in a rat model of mechanical instability-induced peri-implant osteolysis. The rats were treated daily with a GSK-3 beta inhibitor, AR28 (20 mg/kg bw), for up to 5 days. Bone tissue and blood serum were assessed by qRT-PCR, immunohistochemistry, and ELISA on days 3 and 5, and by micro-CT on day 5. After 3 days of treatment with AR28, mRNA levels of beta-catenin, Runx2, Osterix, Col1 alpha 1, and ALP were increased leading to higher osteoblast numbers compared to vehicle-treated animals. BMP-2 and Wnt16 mRNA levels were downregulated by mechanical instability and this was rescued by GSK-3 beta inhibition. Osteoclast numbers were decreased significantly after 3 days of GSK-3 beta inhibition, which correlated with enhanced OPG mRNA expression. This was accompanied by decreased serum levels of TRAP5b on days 3 and 5. Treatment with AR28 upregulated osteoblast differentiation, while osteoclastogenesis was blunted, leading to increased bone mass by day 5. These data suggest that GSK-3 beta inactivation suppresses osteolysis through regulating both osteoblast and osteoclast differentiation in a rat model of instability-induced osteolysis.
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| 5. |
- Amirhosseini, Mehdi, et al.
(author)
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Mechanical instability and titanium particles induce similar transcriptomic changes in a rat model for periprosthetic osteolysis and aseptic loosening
- 2017
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In: Bone Reports. - : Elsevier. - 2352-1872. ; 7, s. 17-25
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Journal article (peer-reviewed)abstract
- Wear debris particles released from prosthetic bearing surfaces and mechanical instability of implants are two main causes of periprosthetic osteolysis. While particle-induced loosening has been studied extensively, mechanisms through which mechanical factors lead to implant loosening have been less investigated. This study compares the transcriptional profiles associated with osteolysis in a rat model for aseptic loosening, induced by either mechanical instability or titanium particles. Rats were exposed to mechanical instability or titanium particles. After 15 min, 3, 48 or 120 h from start of the stimulation, gene expression changes in periprosthetic bone tissue was determined by microarray analysis. Microarray data were analyzed by PANTHER Gene List Analysis tool and Ingenuity Pathway Analysis (IPA). Both types of osteolytic stimulation led to gene regulation in comparison to unstimulated controls after 3, 48 or 120 h. However, when mechanical instability was compared to titanium particles, no gene showed a statistically significant difference (fold change = ± 1.5 and adjusted p-value = 0.05) at any time point. There was a remarkable similarity in numbers and functional classification of regulated genes. Pathway analysis showed several inflammatory pathways activated by both stimuli, including Acute Phase Response signaling, IL-6 signaling and Oncostatin M signaling. Quantitative PCR confirmed the changes in expression of key genes involved in osteolysis observed by global transcriptomics. Inflammatory mediators including interleukin (IL)-6, IL-1ß, chemokine (C-C motif) ligand (CCL)2, prostaglandin-endoperoxide synthase (Ptgs)2 and leukemia inhibitory factor (LIF) showed strong upregulation, as assessed by both microarray and qPCR. By investigating genome-wide expression changes we show that, despite the different nature of mechanical implant instability and titanium particles, osteolysis seems to be induced through similar biological and signaling pathways in this rat model for aseptic loosening. Pathways associated to the innate inflammatory response appear to be a major driver for osteolysis. Our findings implicate early restriction of inflammation to be critical to prevent or mitigate osteolysis and aseptic loosening of orthopedic implants.
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