Osteoporosis: An Age-Related and Gender-Specific Disease – A Mini-Review

Osteoporosis, a classical age-related disease and known to be more common in women than in men, has been reported increasingly often in men during the past few years. Although men at all ages after puberty have larger bones than women, resulting in greater bending strength, mortality after a hip fracture, one of the major complications of osteoporosis, is more common in men than in women. Sex hormone deficiency is associated with unrestrained osteoclast activity and bone loss. Even though estrogen deficiency is more pronounced in women, it appears to be a major factor in the pathogenesis of osteoporosis in both genders. In contrast to osteoporosis in postmenopausal women, the treatment of osteoporosis in men has been scarcely reported. Nevertheless, some drugs commonly used for the treatment of osteoporosis in women also appear to be effective in men. The aim of this study is to review primary osteoporosis in the elderly with particular emphasis on gender-related aspects.Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Glucocorticoids suppress Wnt16 expression in osteoblasts in vitro and in vivo

Glucocorticoid-induced osteoporosis is a frequent complication of systemic glucocorticoid (GC) therapy and mainly characterized by suppressed osteoblast activity. Wnt16 derived from osteogenic cells is a key determinant of bone mass. Here, we assessed whether GC suppress bone formation via inhibiting Wnt16 expression. GC treatment with dexamethasone (DEX) decreased Wnt16 mRNA levels in murine bone marrow stromal cells (mBMSCs) time- and dose-dependently. Similarly, Wnt16 expression was also suppressed after DEX treatment in calvarial organ cultures. Consistently, mice receiving GC-containing slow-release prednisolone pellets showed lower skeletal Wnt16 mRNA levels and bone mineral density than placebo-treated mice. The suppression of Wnt16 by GCs was GC-receptor-dependent as co-treatment of mBMSCs with DEX and the GR antagonist RU-486 abrogated the GC-mediated suppression of Wnt16. Likewise, DEX failed to suppress Wnt16 expression in GR knockout-mBMSCs. In addition, Wnt16 mRNA levels were unaltered in bone tissue of GC-treated GR dimerization-defective GRdim mice, suggesting that GCs suppress Wnt16 via direct DNA-binding mechanisms. Consistently, DEX treatment reduced Wnt16 promoter activity in MC3T3-E1 cells. Finally, recombinant Wnt16 restored DEX-induced suppression of bone formation in mouse calvaria. Thus, this study identifies Wnt16 as a novel target of GC action in GC-induced suppression of bone formation

Postembryonic development and aging of the appendicular skeleton in Ambystoma mexicanum

Background: The axolotl is a key model to study appendicular regeneration. The limb complexity resembles that of humans in structure and tissue components; however, axolotl limbs develop postembryonically. In this work, we evaluated the postembryonic development of the appendicular skeleton and its changes with aging. Results: The juvenile limb skeleton is formed mostly by Sox9/Col1a2 cartilage cells. Ossification of the appendicular skeleton starts when animals reach a length of 10 cm, and cartilage cells are replaced by a primary ossification center, consisting of cortical bone and an adipocyte-filled marrow cavity. Vascularization is associated with the ossification center and the marrow cavity formation. We identified the contribution of Col1a2-descendants to bone and adipocytes. Moreover, ossification progresses with age toward the epiphyses of long bones. Axolotls are neotenic salamanders, and still ossification remains responsive to l-thyroxine, increasing the rate of bone formation. Conclusions: In axolotls, bone maturation is a continuous process that extends throughout their life. Ossification of the appendicular bones is slow and continues until the complete element is ossified. The cellular components of the appendicular skeleton change accordingly during ossification, creating a heterogenous landscape in each element. The continuous maturation of the bone is accompanied by a continuous body growth.Fil: Riquelme Guzmán, Camilo. Technische Universität Dresden; AlemaniaFil: Schuez, Maritta. Technische Universität Dresden; AlemaniaFil: Böhm, Alexander. Technische Universität Dresden; AlemaniaFil: Knapp, Dunja. Technische Universität Dresden; AlemaniaFil: Edwards Jorquera, Sandra. Technische Universität Dresden; AlemaniaFil: Ceccarelli, Alberto Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Chara, Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Argentina de la Empresa; Argentina. Technische Universität Dresden; AlemaniaFil: Rauner, Martina. Universitätsklinikum Carl Gustav Carus; AlemaniaFil: Sandoval Guzmán, Tatiana. Universitätsklinikum Carl Gustav Carus; Alemania. Technische Universität Dresden; Alemani

Osteoprotegerin production by breast cancer cells is suppressed by dexamethasone and confers resistance against TRAIL-induced apoptosis

ABSTRACT Osteoprotegerin (OPG) is a decoy receptor for receptor activator of NF-kB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). While RANKL is essential for osteoclastogenesis and facilitates breast cancer migration into bone, TRAIL promotes breast cancer apoptosis. We analyzed the expression of OPG and TRAIL and its modulation in estrogen receptor-positive MCF-7 cells and receptor-negative MDA-MB-231 cells. In both cells, OPG mRNA levels and protein secretion were dose-and time-dependently enhanced by interleukin (IL)-1b and suppressed by dexamethasone. In contrast to MCF-7 cells, MDA-MB-231 abundantly expressed TRAIL mRNA, which was enhanced by IL-1b and inhibited by dexamethasone. TRAIL activated pro-apoptotic caspase-3, -7, and poly-ADP-ribose polymerase and decreased cell numbers of MDA-MB-231, but had no effect on MCF-7 cells. Gene silencing siRNA directed against OPG resulted in a 31% higher apoptotic rate compared to non-target siRNA-treated MDA-MB-231 cells. Furthermore, TRAIL induced significantly less apoptosis in cells cultured in conditioned media (containing OPG) compared to cells exposed to TRAIL in fresh medium lacking OPG ( P < 0.01) and these protective effects were reversed by blocking OPG with its specific ligand RANKL ( P < 0.05). The association between cancer cell survival and OPG production by MDA-MB-231 cells was further supported by the finding, that modulation of OPG secretion using IL-1b or dexamethasone prior to TRAIL exposure resulted in decreased and increased rate of apoptosis, respectively ( P < 0.05). Thus, OPG secretion by breast cancer cells is modulated by cytokines and dexamethasone, and may represent a critical resistance mechanism that protects against TRAIL-induced apoptosis

Aspalathin from Aspalathus linearis (rooibos) reduces osteoclast activity and increases osteoblast activity in vitro

Bone remodelling in a healthy body is in constant balance, maintaining an adaptive and robust skeletal system. In osteoporosis this balance is disrupted with the rates of osteoclastic bone resorption exceeding osteoblastic bone formation, resulting in lower bone mineral density. Rooibos tea, is a popular South African drink made from Aspalathus linearis leaves grown in the Western Cape. This tea is rich in phenolic compounds which have been widely investigated in recent years as a potential treatment for many ailments. In this study, aspalathin, a phenolic compound found exclusively in rooibos, increases osteoblast formation and function including increased osteoblast marker expression and mineralisation. In addition, aspalathin decreased differentiation and function of osteoclasts as well as reducing osteoclast formation in an osteoclast/osteoblast co-culture model. These results illustrate bone-protective effects of aspalathin in vitro through the reduction of osteoclast activity and promotion of osteoblast activity, with potential applications in the maintenance of bone density.The University of Pretoria Postgraduate Study Abroad Bursary Program, the Institute for Food, Nutrition, and Well-being, University of Pretoria, and Biocom Biotech, Centurion, South Africa.https://www.elsevier.com/locate/jffam2020Human NutritionPhysiolog

Increased pore size of scaffolds improves coating efficiency with sulfated hyaluronan and mineralization capacity of osteoblasts

Background: Delayed bone regeneration of fractures in osteoporosis patients or of critical-size bone defects after tumor resection are a major medical and socio-economic challenge. Therefore, the development of more effective and osteoinductive biomaterials is crucial. Methods: We examined the osteogenic potential of macroporous scaffolds with varying pore sizes after biofunctionalization with a collagen/high-sulfated hyaluronan (sHA3) coating in vitro. The three-dimensional scaffolds were made up from a biodegradable three-armed lactic acid-based macromer (TriLA) by cross-polymerization. Templating with solid lipid particles that melt during fabrication generates a continuous pore network. Human mesenchymal stem cells (hMSC) cultivated on the functionalized scaffolds in vitro were investigated for cell viability, production of alkaline phosphatase (ALP) and bone matrix formation. Statistical analysis was performed using student's t-test or two-way ANOVA. Results: We succeeded in generating scaffolds that feature a significantly higher average pore size and a broader distribution of individual pore sizes (HiPo) by modifying composition and relative amount of lipid particles, macromer concentration and temperature for cross-polymerization during scaffold fabrication. Overall porosity was retained, while the scaffolds showed a 25% decrease in compressive modulus compared to the initial TriLA scaffolds with a lower pore size (LoPo). These HiPo scaffolds were more readily coated as shown by higher amounts of immobilized collagen (+ 44%) and sHA3 (+ 25%) compared to LoPo scaffolds. In vitro, culture of hMSCs on collagen and/or sHA3-coated HiPo scaffolds demonstrated unaltered cell viability. Furthermore, the production of ALP, an early marker of osteogenesis (+ 3-fold), and formation of new bone matrix (+ 2.5-fold) was enhanced by the functionalization with sHA3 of both scaffold types. Nevertheless, effects were more pronounced on HiPo scaffolds about 112%. Conclusion: In summary, we showed that the improvement of scaffold pore sizes enhanced the coating efficiency with collagen and sHA3, which had a significant positive effect on bone formation markers, underlining the promise of using this material approach for in vivo studies. © 2019 The Author(s)

Transferrin receptor 2 controls bone mass and pathological bone formation via BMP and Wnt signalling

Transferrin receptor 2 (Tfr2) is mainly expressed in the liver and controls iron homeostasis. Here, we identify Tfr2 as a regulator of bone homeostasis that inhibits bone formation. Mice lacking Tfr2 display increased bone mass and mineralization independent of iron homeostasis and hepatic Tfr2. Bone marrow transplantation experiments and studies of cell-specific Tfr2 knockout mice demonstrate that Tfr2 impairs BMP-p38MAPK signaling and decreases expression of the Wnt inhibitor sclerostin specifically in osteoblasts. Reactivation of MAPK or overexpression of sclerostin rescues skeletal abnormalities in Tfr2 knockout mice. We further show that the extracellular domain of Tfr2 binds BMPs and inhibits BMP-2-induced heterotopic ossification by acting as a decoy receptor. These data indicate that Tfr2 limits bone formation by modulating BMP signaling, possibly through direct interaction with BMP either as a receptor or as a co-receptor in a complex with other BMP receptors. Finally, the Tfr2 extracellular domain may be effective in the treatment of conditions associated with pathological bone formation

Exploiting Mass Spectrometry to Unlock the Mechanism of Nanoparticle-Induced Inflammasome Activation

Nanoparticles (NPs) elicit sterile inflammation, but the underlying signaling pathways are poorly understood. Here, we report that human monocytes are particularly vulnerable to amorphous silica NPs, as evidenced by single-cell-based analysis of peripheral blood mononuclear cells using cytometry by time-of-flight (CyToF), while silane modification of the NPs mitigated their toxicity. Using human THP-1 cells as a model, we observed cellular internalization of silica NPs by nanoscale secondary ion mass spectrometry (nanoSIMS) and this was confirmed by transmission electron microscopy. Lipid droplet accumulation was also noted in the exposed cells. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed specific changes in plasma membrane lipids, including phosphatidylcholine (PC) in silica NP-exposed cells, and subsequent studies suggested that lysophosphatidylcholine (LPC) acts as a cell autonomous signal for inflammasome activation in the absence of priming with a microbial ligand. Moreover, we found that silica NPs elicited NLRP3 inflammasome activation in monocytes, whereas cell death transpired through a non-apoptotic, lipid peroxidation-dependent mechanism. Together, these data further our understanding of the mechanism of sterile inflammation

Prevalence and incidence of iron deficiency in European community-dwelling older adults : An observational analysis of the DO-HEALTH trial

Background and aim Iron deficiency is associated with increased morbidity and mortality in older adults. However, data on its prevalence and incidence among older adults is limited. The aim of this study was to investigate the prevalence and incidence of iron deficiency in European community-dwelling older adults aged ≥ 70 years. Methods Secondary analysis of the DO-HEALTH trial, a 3-year clinical trial including 2157 community-dwelling adults aged ≥ 70 years from Austria, France, Germany, Portugal and Switzerland. Iron deficiency was defined as soluble transferrin receptor (sTfR) > 28.1 nmol/L. Prevalence and incidence rate (IR) of iron deficiency per 100 person-years were examined overall and stratified by sex, age group, and country. Sensitivity analysis for three commonly used definitions of iron deficiency (ferritin  1.5) were also performed. Results Out of 2157 participants, 2141 had sTfR measured at baseline (mean age 74.9 years; 61.5% women). The prevalence of iron deficiency at baseline was 26.8%, and did not differ by sex, but by age (35.6% in age group ≥ 80, 29.3% in age group 75–79, 23.2% in age group 70–74); P  1.5. Occurrences of iron deficiency were observed with IR per 100 person-years of 9.2 (95% CI 8.3–10.1) and did not significantly differ by sex or age group. The highest IR per 100 person-years was observed in Austria (20.8, 95% CI 16.1–26.9), the lowest in Germany (6.1, 95% CI 4.7–8.0). Regarding the other definitions of iron deficiency, the IR per 100 person-years was 4.5 (95% CI 4.0–4.9) for ferritin  1.5. Conclusions Iron deficiency is frequent among relatively healthy European older adults, with people aged ≥ 80 years and residence in Austria and Portugal associated with the highest risk

The aging osteoblast : investigation mechanisms of osteoblast dysfunction with aging

Die altersbedingte Osteoporose ist durch eine verminderte Knochenstärke charakterisiert und prädisponiert ältere Menschen zu einem erhöhten Frakturrisiko. Der Knochenverlust ist durch eine erniedrigte Knochenformationsrate im Verhältnis zur Knochenresorptionsrate gekennzeichnet. Auf zellulärer Ebene kann man eine Steigerung in der Anzahl und Aktivität der Osteoklasten feststellen, wobei die Generation und Funktion von Osteoblasten deutlich abnimmt. Obwohl die verminderte Funktion von Osteoblasten im Alter in zahlreichen Humanstudien und Tiermodellen gezeigt wurde, bleiben die Ursachen und die zu Grunde liegenden molekularen Mechanismen weitgehend unbekannt. In dieser Studie habe ich mögliche Ursachen (Teil I) und molekulare Mechanismen (Teil III), die zur verminderten Osteoblastogenese im Alter führen, sowie Konsequenzen der beeinträchtigten Osteoblastendifferenzierung untersucht (Teil II). Runx2 und Osterix sind essentielle osteoblastenspezifische Transkriptionsfaktoren. Der Einfluss des Alterns auf ihre Expression ist jedoch wenig erforscht. Weiters wurde der Wnt Signalweg als Regulator der Knochenmasse identifiziert, da er die Osteoblastogenese beeinflusst, und vor kurzem wurde dieser Signalweg mit altersassoziierten Prozessen in Verbindung gebracht. Der Einfluss des Alterns auf die Expression von Komponenten des Wnt Signalweges im Knochen bzw. in Osteoblasten wurde allerdings noch nicht untersucht. Ziel dieser Studie war daher die Untersuchung des Einflusses des Alterns auf die Genexpression von Runx2 und Osterix sowie auf extrazellulären Komponenten des Wnt Signalweges. Osteoblasten wurden aus dem Knochenmark von jeweils sechs männlichen C57BL/6 Mäusen gewonnen, die 6-Wochen, 6-Monate oder 18-Monate alt waren. Das Differenzierungspotential wurde mit einer Alizarin S Färbung untersucht. Die Genexpression von Runx2, Osterix, Wnt1, 3a, 4, 5a, 5b, 7b, 9b, 10b, LRP-5/6, sowie Dkk-1, Sklerostin, and sFRP-1 wurde mittels quantitativer RT-PCR im Knochengewebe sowie während der Osteoblastendifferenzierung analysiert. Meine Ergebnisse zeigen, dass die Osteoblastendifferenzierung im Alter signifikant vermindert war. Die Expression von Runx2 und Osterix sowie sämtlicher Wnt Proteine im Knochen war in alten Mäusen vermindert. Reife Osteoblasten alter Mäuse verglichen zu jenen junger Mäuse zeigten eine signifikant erhöhte Expression von Wnt9b, LRP-6 und Dkk-1, wohingegen die Expression von Wnt5a und 7b vermindert war. Bei unreifen Osteoblasten führte das Altern zu einer vermehrten Expression on Wnt1, 5a, 5b und 7b, wohingegen die Expression von Runx2 und Osterix deutlich vermindert war. Die Genexpression von Wnt3a, 4, LRP-5 und Sklerostin blieb vom Altern unbeeinflusst. Unsere Ergebnisse zeigen dass die Expression von Runx2 und Osterix bei alten Mäusen vermindert ist und lassen daher eine mögliche Ursache der insuffizienten Osteoblastendifferenzierung schließen. Weiters konnten wir zeigen, dass das Altern die Expression jedes einzelnen osteoblastären Wnt Proteins individuell beeinflusst. Die größtenteils verminderte Expression von Wnt Proteinen im Knochengewebe unterstreicht die kürzlich entdeckte Assoziation des Wnt Signalweges mit dem Altern. Als nächstes wurde die altersabhängige Expression von RANKL und OPG untersucht, da diese Proteine maßgeblich an der Regulation der Osteoklastogenese beteiligt sind. Ihre Expression wurde im selben Ansatz wie oben beschrieben untersucht. Zusätzlich wurde die Expression genannter Gene in T Zellen untersucht. Die RANKL/OPG Ratio war im Knochen sowie in reifen Osteoblasten alter Mäuse tendentiell erhöht. Im Gegensatz dazu war die Anzahl der RANKL-positiven CD4+ und CD8+ T Zellen in jungen Mäusen erhöht. Folglich dürfte das gesteigerte Potential des Knochenmarks Osteoklasten zu generieren durch die erhöhte RANKL/OPG Ratio in Osteoblasten bedingt sein, während die RANKL-Produktion in T Zellen eine untergeordnete Rolle spielen dürfte. Der dritte Teil dieser Studie befasste sich mit der Untersuchung eines möglichen Mechanismus der zur alterbedingten Osteoblasteninsuffizienz führen könnte und auf dem Verlust des nukleären Proteins Lamin A/C basiert. Mutationen im Lamin A/C-Gen führen zum Hutchinson-Gilford Progerie Syndrom (HGPS), welches durch eine verfrühten Vergreisung sowie Osteoporose charakterisiert ist. In diesem Projekt habe ich die Rolle von Lamin A/C auf die Osteoblastendifferenzierung sowie auf mögliche sekundäre Auswirkungen auf die Osteoklastogenese untersucht. Dafür wurde die Expression von Lamin A/C während der Osteoblastendifferenzierung mittels siRNAs ausgeschaltet. Dies führte zu einer Verminderung der Osteoblastenproliferation um 26% und der Osteoblastendifferenzierung um 48%. Weiters zeigten Osteoblasten mit einer verminderten Expression von Lamin A/C eine reduzierte mRNA Expression von Runx2 und mRNA und Proteinexpression von Osteokalzin. Die Verminderung in der Expression von Lamin A/C führte außerdem zu einer Steigerung der RANKL/OPG Ratio. Dies führte zu einem erhöhten Potential der Osteoblasten die Osteoklastogenese zu fördern und war durch eine um 34% erhöhte Osteoklastenzahl gekennzeichnet. Die gewonnenen Daten zeigen, dass Lamin A/C essentiell ist für die Osteoblastendifferenzierung und dass eine Verminderung in der Lamin A/C Expression zu einer erhöhten Osteoklastogenese führt. Da Lamin A/C im Progeriesyndrom HGPS mutiert ist, decken meine Daten eine neue Verbindung zwischen einem verminderten Expressionsspiegel von Lamin A/C und einer insuffizienten Osteoblastendifferenzierung auf. Zusammenfassend konnte die vorliegende Studie zeigen, dass die Osteoblastendifferenzierung mit dem Alter abnimmt. Da das Altern zur einer verminderten Expression von verschiedenen Wnt Liganden und Lamin A/C führt und diese Faktoren essentiell für die Reifung und Funktion der Osteoblasten sind, kann davon ausgegangen werden, dass diese Mechanismen zur beeinträchtigten Reifung und Funktion der Osteoblasten im Alter beitragen.Age-related osteoporosis is characterized by compromised strength predisposing the elderly to an increased fracture risk. It is hallmarked by a decreased bone formation rate, relative to bone resorption, and is reflected by decreased osteoblastogenesis compared to osteoclastogenesis. Although impaired osteoblast function has been identified in various aging studies in humans and rodents, only few studies have been undertaken to investigate the molecular mechanisms of attenuated osteoblast differentiation. In this study we have assessed possible causes (part I) and consequences (part II) of impaired osteoblast differentiation with aging, as well as mechanisms involved (part III). Runx2 and osterix have been identified as essential osteoblast transcription factors, but their regulation with aging is poorly investigated. Moreover, the Wnt signaling pathway has been shown to be a major determinant of bone mass as it regulates osteoblastogenesis, and recently, this pathway has been linked to age-related processes. However, their age-related expression pattern has not been assessed in bone or osteoblasts. Thus, we have investigated the impact of aging on the mRNA expression of runx2 and osterix, and extracellular components of the Wnt signaling pathway in order to define possible causes of age-related impairment of osteoblastogenesis. Bone marrow cells were isolated from six male C57BL/6 mice, aged 6-weeks, 6-months, and 18-months. Osteogenic differentiation was induced for three weeks and assessed using alizarin red staining. Gene expression of runx2, osterix, Wnt1, 3a, 4, 5a, 5b, 7b, 9b, 10b, lipoprotein receptor-related protein (LRP)-5/6, as well as dickkopf-1 (Dkk-1), sclerostin, and secreted frizzled related protein-1 (sFRP-1) was determined in bone tissue and osteoblasts at days 7, 14, and 21 by real-time RT-PCR. We found that osteoblast differentiation was significantly reduced in aged mice. In bone tissue, expression levels of runx2 and osterix, and all Wnt genes assessed were decreased in old mice. Mature osteoblasts of aged compared to those of young mice showed enhanced expression of Wnt9b, LRP-6, and Dkk-1, and decreased expression of Wnt5a and 7b. In early osteoblasts, mRNA levels of Wnt1, 5a, 5b, and 7b were increased significantly in aged mice while those of runx2 and osterix were significantly decreased. The expression of Wnt3a, 4, LRP-5, and sclerostin was not altered in aged osteoblasts. In conclusion, the decreased expression of runx2 and osterix in aged animals may partially account for the impaired osteoblast differentiation seen with aging. Moreover, the osteoblastic expression of each Wnt-related protein is regulated individually by aging and the overall decreased expression of Wnt-related proteins in bone tissue of aged mice underlines the newly discovered association of Wnt signaling with aging. Secondly, we have assessed the age-related expression pattern of receptor activator of NFB ligand (RANKL) and osteoprotegerin (OPG), as they are critical osteoblast-produced regulators of osteoclastogenesis. The same study design as well as methodological approach as mentioned above was used. The RANKL/OPG ratio in bone tended to increase with aging. Mature osteoblasts from old animals displayed a higher RANKL/OPG ratio. Contrary, in young mice a higher percentage of CD4+ and CD8+ T cells expressed RANKL was apparent compared to adult and old ones. Nevertheless, our results suggest that the increased osteoclastogenic potential found in the bone marrow of old mice may be caused by the enhanced RANKL/OPG ratio in osteoblasts, which are the main producers of RANKL and OPG. Lastly, we have assessed mechanisms of age-related osteoblast insufficiency due to loss of the nuclear lamina protein lamin A/C. Recently, the Hutchinson-Gilford progeria syndrome (HGPS), a disease of accelerated aging and premature osteoporosis, has been linked to mutations in the gene encoding for lamin A/C. Here, we tested whether inhibition of lamin A/C in osteoblastic lineage cells impairs osteoblastogenesis and accelerates osteoclastogenesis. Lamin A/C was continuously knocked-down using small interfering (si)RNAs in human mesenchymal stem cells (MSCs) differentiating towards osteoblasts. Lamin A/C knock-down led to an inhibition of osteoblast proliferation by 26%, and impaired osteoblast differentiation by 48% based on mineralized matrix formation assessed with alizarin red S staining. Expression levels of runx2 and osteocalcin mRNA were decreased in mature lamin A/C-knock-down osteoblasts by 44% and 78%, respectively. Furthermore, Western blot analysis showed that osteoblasts with diminished levels of lamin A/C also produced less osteocalcin. Lamin A/C inhibition increased the RANKL/OPG ratio at mRNA and protein levels, resulting in an enhanced ability to support osteoclastogenesis, as reflected by a 34% increase of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. Our data indicate that lamin A/C is essential for proper osteoblastogenesis and therefore may link lamin A/C to age-related impairment of osteoblast differentiation. Moreover, lack of lamin A/C favors an osteoclastogenic milieu, and results in enhanced osteoclastogenesis. Taken together, our study demonstrates that aging negatively affects osteoblast differentiation. We propose that this may be the result of the down-regulated expression of various Wnt ligands and lamin A/C, which both have been shown to be vital factors for osteoblast differentiation and function.submitted by Martina RaunerWien, Med. Univ., Diss., 200