In vitro determination of biomechanical properties of human articular cartilage in osteoarthritis using multi-parametric MRI.

The objective of this study was to evaluate the correlations between MR parameters and the biomechanical properties of naturally degenerated human articular cartilage. Human cartilage explants from the femoral condyles of patients who underwent total knee replacement were evaluated on a micro-imaging system at 3T. To quantify glycosaminoglycan (GAG) content, delayed gadolinium-enhanced MRI of the cartilage (dGEMRIC) was used. T(2) maps were created by using multi-echo, multi-slice spin echo sequences with six echoes: 15, 30, 45, 60, 75, and 90 ms. Data for apparent diffusion constant (ADC) maps were obtained from pulsed gradient spin echo (PGSE) sequences with five b-values: 10.472, 220.0, 627.0, 452.8, 724.5, and 957.7. MR parameters were correlated with mechanical parameters (instantaneous (I) and equilibrium (Eq) modulus and relaxation time (tau)), and the OA stage of each cartilage specimen was determined by histological evaluation of hematoxylin-eosin stained slices. For some parameters, a high correlation was found: the correlation of T(1Gd) vs Eq (r=0.8095), T(1Gd) vs I/Eq (r=-0.8441) and T(1Gd) vs tau (r=0.8469). The correlation of T(2) and ADC with selected biomechanical parameters was not statistically significant. In conclusion, GAG content measured by dGEMRIC is highly related to the selected biomechanical properties of naturally degenerated articular cartilage. In contrast, T(2) and ADC were unable to estimate these properties. The results of the study imply that some MR parameters can non-invasively predict the biomechanical properties of degenerated articular cartilage.

Mapping the structure and function of the E1 and E2 glycoproteins in alphaviruses.

The 9 A resolution cryo-electron microscopy map of Sindbis virus presented here provides structural information on the polypeptide topology of the E2 protein, on the interactions between the E1 and E2 glycoproteins in the formation of a heterodimer, on the difference in conformation of the two types of trimeric spikes, on the interaction between the transmembrane helices of the E1 and E2 proteins, and on the conformational changes that occur when fusing with a host cell. The positions of various markers on the E2 protein established the approximate topology of the E2 structure. The largest conformational differences between the icosahedral surface spikes at icosahedral 3-fold and quasi-3-fold positions are associated with the monomers closest to the 5-fold axes. The long E2 monomers, containing the cell receptor recognition motif at their extremities, are shown to rotate by about 180 degrees and to move away from the center of the spikes during fusion.

Identification of essential regions in the cytoplasmic tail of interleukin-1 receptor accessory protein critical for interleukin-1 signaling.

Interleukin (IL)-1 plays an important role in inflammation and regulation of immune responses. The activated IL-1 receptor complex, which consists of the IL-1 receptor type I and the IL-1 receptor accessory protein (IL-1RAcP), generates multiple cellular responses including NF-kappaB activation, IL-2 secretion, and IL-2 promoter activation. Reconstitution experiments in EL4D6/76 cells lacking IL-1RAcP expression and IL-1 responsiveness were used to analyze structure-function relationships of the IL-1RAcP cytoplasmic tail. Mutating a potential tyrosine kinase phosphorylation motif and various conserved amino acid (aa) residues had no effect on IL-1 responsiveness. Truncation analyses revealed that box 3 of the TIR domain was required for NF-kappaB activation, IL-2 production, and c-Jun N-terminal kinase (JNK) activation, whereas IL-2 promoter activation was only partially inhibited. Surprisingly, deletion of aa 527-534 resulted in almost complete loss of all IL-1 responsiveness. Replacement of these aa with alanyl residues did not reconstitute NF-kappaB activation, IL-2 production, or JNK activation but partly restored IL-2 promoter activation. Immunoprecipitation data revealed a strong correlation between MyD88 binding with NF-kappaB activation and IL-2 production but not with IL-2 promoter activation. Taken together, our data indicate that box 3 of IL-1RAcP is critical for IL-1-dependent NF-kappaB activation and stabilization of IL-2 mRNA via JNK, whereas aa 527-534 largely contribute to IL-2 promoter activation.