During development and homeostasis, precise control of Wnt/β-catenin signaling is in part achieved by secreted and membrane proteins that negatively control activity of the Wnt co-receptors Lrp5 and Lrp6. Lrp4 is related to Lrp5/6 and is implicated in modulation of Wnt/β-catenin signaling, presumably through its ability to bind to the Wise (Sostdc1)/sclerostin (Sost) family of Wnt antagonists. To gain insights into the molecular mechanisms of Lrp4 function in modulating Wnt signaling, we performed an array of genetic analyses in murine tooth development, where Lrp4 and Wise play important roles. We provide genetic evidence that Lrp4 mediates the Wnt inhibitory function of Wise and also modulates Wnt/β-catenin signaling independently of Wise. Chimeric receptor analyses raise the possibility that the Lrp4 extracellular domain interacts with Wnt ligands, as well as the Wnt antagonists. Diverse modes of Lrp4 function are supported by severe tooth phenotypes of mice carrying a human mutation known to abolish Lrp4 binding to Sost. Our data suggest a model whereby Lrp4 modulates Wnt/β-catenin signaling via interaction with Wnt ligands and antagonists in a context-dependent manner.

BackgroundAs the resident stem cells of skeletal muscle, satellite cells are activated by extracellular cues associated with local damage. Once activated, satellite cells will re-enter the cell cycle to proliferate and supply a population of myoblasts, which will repair or replace damaged myofibers by differentiating and fusing either with an existing myofiber or with each other. There is also evidence that the orientation of cell division with respect to the myofiber may indicate or convey asymmetry in the two daughter cells. Our recent studies with time-lapse imaging of myofiber-associated satellite cells in vitro have yielded new data on the timing and orientation of satellite cell divisions, and revealed persistent differences in the behavior of daughter cells from planar versus vertical divisions.ResultsWe analyzed 244 individual fiber-associated satellite cells in time-lapse video from 24 to 48 hours after myofiber harvest. We found that initial cell division in fiber culture is not synchronous, although presumably all cells were activated by the initial trauma of harvest; that cell cycling time is significantly shorter than previously thought (as short as 4.8 hours, averaging 10 hours between the first and second divisions and eight hours between the second and third); and that timing of subsequent divisions is not strongly correlated with timing of the initial division. Approximately 65% of first and 80% of second cell divisions occur parallel to the axis of the myofiber, whereas the remainder occur outside the plane of the fiber surface (vertical division). We previously demonstrated that daughter cells frequently remain associated with each other after division or reassociate after a brief separation, and that unrelated cells may also associate for significant periods of time. We show in this paper that daughter cells resulting from a vertical division remain associated with one another several times longer than do daughters from a horizontal division. However, the total average time of association between sister cells is not significantly different from the total average time of association between unrelated cells.ConclusionsThese longitudinal characterizations of satellite cell behavior shortly after activation provide new insights into cell proliferation and association as a function of relatedness, and indicate significant and consistent heterogeneity within the population based on these metrics.

The importance of bone morphogenetic protein 2 (BMP2) in the skeleton is well known. BMP2 is expressed in a variety of tissues during development, growth and healing. In this study we sought to better identify the role of tissue-specific BMP2 during post-natal growth and to determine if BMP2 knockout affects the ability of terminally differentiated cells to create high quality bone material. We targeted BMP2 knockout to two differentiated cell types known to express BMP2 during growth and healing, early-stage osteoblasts and their progeny (osterix promoted Cre) and vascular endothelial cells (vascular-endothelial-cadherin promoted Cre). Our objectives were to assess post-natal bone growth, structure and strength. We hypothesized that removal of BMP2 from osteogenic and vascular cells (separately) would result in smaller skeletons with inferior bone material properties. At 12 and 24 weeks of age the osteoblast knockout of BMP2 reduced body weight by 20%, but the vascular knockout had no effect. Analysis of bone in the tibia revealed reductions in cortical and cancellous bone size and volume in the osteoblast knockout, but not in the vascular endothelial knockout. Furthermore, forelimb strength testing revealed a 30% reduction in ultimate force at both 12 and 24 weeks in the osteoblast knockout of BMP2, but no change in the vascular endothelial knockout. Moreover, mechanical strength testing of femurs from osteoblast knockout mice demonstrated an increased Young’s modulus (greater than 35%) but decreased post-yield displacement (greater than 50%) at both 12 and 24 weeks of age. In summary, the osteoblast knockout of BMP2 reduced bone size and altered mechanical properties at the whole-bone and material levels. Osteoblast-derived BMP2 has an important role in post-natal skeletal growth, structure and strength, while vascular endothelial-derived BMP2 does not.

Purpose:Although minimally invasive (robotic or laparoscopic) abdominal sacrocolpopexy (MISC) has become the new gold standard for durable pelvic organ prolapse repair after the vaginal mesh controversy, current literature is limited. Our objective was to study reoperation for mesh complications after MISC.Materials and Methods:All women undergoing MISC in California from January 2012 to December 2018 were identified from Office of Statewide Health Planning and Development data sets using appropriate ICD-9/10 (International Classification of Diseases 9th/10th Revision) and CPT® (Current Procedural Terminology) codes. Univariate and multivariable analyses were performed to assess associations between patient demographics, surgical details and our primary outcomes: rates of reoperation for a mesh complication.Results:Of 12,189 women undergoing MISC 8,398 (68.9%) had concomitant hysterectomy. Total hysterectomy (TH) and supracervical hysterectomy (SCH) were performed in 5,027 (41.2%) and 3,371 (27.6%) cases, respectively. Reoperation rates for mesh complications were lower after SCH vs TH (overall: 0.7%, mean followup time 1,111 days vs 3.1%, mean followup time 1,095 days, p <0.001; subcohort with at least 4 years of followup: 2.1% vs 8.9%, p <0.001). Additionally, mesh complication rates were higher even if TH was performed remotely, as compared to concomitant SCH (5.2% vs 0.7%, p <0.001). The increased risk for reoperation due to mesh complications after TH was preserved on multivariable analysis (OR 4.20, 95% CI 2.72‒6.50, p <0.001).Conclusions:Concomitant TH at time of MISC is associated with a significantly higher rate of mesh complication as compared to SCH. The increased risk of a mesh complication associated with TH is present even if the TH was performed prior to the MISC.

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