Day‐to‐Day Variability in Glomerular Filtration Rate in Normal Dogs by Scintigraphic Technique

The sources of variability in variability of scintigraphic measurements of glomerular filtration rate (GFR) have not been determined. The day to day variability of GFR was studied in 18 healthy beagle dogs. The renal uptake of ^99mTc‐diethylenetri‐aminepentaacetic acid (DTPA) of each dog was measured using a scintigraphic technique three times at intervals of 5–26 days. GFR was calculated from a regression equation relating uptake to plasma clearance, derived in our laboratory. The mean GFR was 3.97 ± 0.72 (SD) ml/min/kg with values from 2.66 to 5.67 ml/min/kg. Analysis of variance (anova ) using a linear mixed model showed that most variability is a result of the dogs, less because of day to day variability and very little to the measurement variability. The repeatability coefficients for the day to day variability and measurement variability were 1.06 and 0.21 ml/min/kg respectively. The day to day variability can be caused by physiological homeostatic adjustments by the kidneys needed because of fluctuations in food and fluid intake, each dog's individual capacity to adjust, and to intrinsic errors in the measurement method. These results should be considered when using the scintigraphic method for clinical evaluation and research.     

Investigation of High‐Speed Erythrocyte Flow and Erythrocyte‐Wall Impact in a Lab‐on‐a‐Chip

To better understand erythrocyte high‐speed motion, collision characteristics, and collision‐induced hemolysis probability in rotary blood pumps, a visual experimental investigation of high‐speed erythrocyte flow and erythrocyte‐wall collision in a lab‐on‐a‐chip was performed. The erythrocyte suspension was driven by a microsyringe pump connected to the microchip, and the erythrocyte flow and erythrocyte‐wall impact process were observed and imaged by an optical microscope and a high‐speed camera. Two types of microchips with different impact surfaces (flat and curved) were employed. The motion and deformation features before and after collision were studied in detail. The results show that erythrocytes not only move along the flow direction in the flow plane but also rotate and roll in three‐dimensional space. Erythrocytes keep discoid shape during the movement in the straight channel, but their deformations during collision are mainly classified into two types: erythrocyte structure is still stable and the erythrocyte performance can be ensured to a certain extent in the TypeA deformation, while the TypeB deformation makes the membrane more likely to fracture on the stretched side, increasing the probability of hemolysis. Furthermore, the movements and deformations of the erythrocytes after collision are analyzed and classified into two types: bouncing and slipping. Moreover, a simulation method for the flow in microchip was performed and validated through a comparison of the streamlines and experimental erythrocytes tracks, which can be further employed to predict the high‐speed blood flow, associated with collision process in mechanical blood pump.     

MicroRNA‐199a‐3p,microRNA‐193b,and microRNA‐320c are correlated to aging and regulate human cartilage metabolism

MicroRNAs (miRNAs) are small RNAs of ～22 base pairs that regulate gene expression. We harvested cartilage tissue from patients with polydactylism, anterior cruciate ligament injury, and osteoarthritis undergoing total knee arthroplasty and used microarrays to identify miRNAs whose expression is upregulated or downregulated with age. The results were assessed by real‐time PCR and MTT assay in a mimic group, in which synthetic double‐stranded RNA from the isolated miRNA was transfected to upregulate expression, and in an inhibitor group, in which the miRNA was bound specifically to downregulate expression. The expression of two miRNAs (miR‐199a‐3p and miR‐193b) was upregulated with age and that of one miRNA (miR‐320c) was downregulated with age. A real‐time PCR assay showed that type 2 collagen, aggrecan, and SOX9 expression were downregulated in the miR‐199a‐3p mimic group but was upregulated in the inhibitor group. Similar results were observed for miR‐193b. By contrast, ADAMTS5 expression was downregulated in the miR‐320c mimic group and upregulated in the inhibitor group. Cell proliferative activity was upregulated significantly in the miR‐193b inhibitor group compared with the control group. We believe that miR‐199a‐3p and miR‐193b are involved in the senescence of chondrocytes, and miR‐320c is involved in the juvenile properties of chondrocytes. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1915–1922, 2012     

Predominant role of PDGF receptor transactivation in Wnt3a‐induced osteoblastic cell proliferation

Previous studies have shown that Wnt3a enhances the proliferation and inhibits the osteogenic differentiation of human mesenchymal stem cells (hMSCs). In this study, we investigated the signaling pathways involved in Wnt3a‐induced osteoblastic cell proliferation. Experiments with DKK1, a natural antagonist of Lrp5/6, indicated that Wnt/β‐catenin did not play a major role in Wnt3a‐induced osteoblastic cell proliferation. The use of selective inhibitors of known mitogenic pathways implicates Src family kinases (SFKs) and a protein kinase C (PKC) in this cellular response. Time‐dependent analysis of signaling molecules activated by Wnt3a in MC3T3‐E1 cells revealed parallel activation of the canonical pathway and of several tyrosine kinases, including SFKs and PDGF receptors (PDGF‐Rs). Functional analysis with specific inhibitors suggested a major role of PDGF‐Rs in mediating Wnt3a‐induced cell proliferation. Further investigation with an si‐RNA approach confirmed a predominant role of this receptor in this cellular response. The use of soluble decoy PDGF‐Rs that can sequester extracellular PDGFs excluding that part of the increased PDGF receptor phosphorylation by Wnt3a was the result of autocrine production of PDGFs. A selective SFK inhibitor blunted the enhanced PDGF‐R phosphorylation and cell proliferation induced by Wnt3a. Studies of initial events involved in the regulation of this pathway suggest a role of dishevelled. In conclusion, data presented in this study indicate that cell proliferation induced by Wnt3a in osteoblastic cells is mediated by a dishevelled‐dependent and β‐catenin‐independent pathway, which involves the transactivation of PDGF receptors. © 2013 American Society for Bone and Mineral Research