Local Validation of a National Orthopaedic Registry.

BACKGROUND/OBJECTIVE: Registries are limited by the quality of the data they collect. We aimed to measure the data entry error rate at a regional orthopaedic unit in a national arthroplasty registry and to assess a proposed intervention of restricting data entry to senior trainees. METHODS AND MATERIALS: A total of 200 primary and revision arthroplasty cases (119 hips, 81 knees) were randomly selected from a single year, 2020. The Irish National Orthopaedic Registry was examined for the grade of the trainee that populated the form and the accuracy of 24 parameters by comparison with data recorded elsewhere in the patient record. RESULTS: The mean number of errors per form was 2.17 (95% confidence interval (CI): 1.95-2.39), giving an overall error rate of 9% (95% CI: 8%-10.0%). Eighty-seven percent of forms examined contained inaccuracies, ranging from one to nine errors (4%-38%). Some parameters were more prone to errors, ranging from 1% to 28%. There was no evidence of total errors varying by trainee grade (analysis of variance (ANOVA) p-value: 0.34). CONCLUSIONS: Error rates were in line with the literature. Results did not support restricting data entry to senior trainees.

High capacity of the endoplasmic reticulum to prevent secretion and aggregation of amyloidogenic proteins.

Protein aggregation is associated with neurodegeneration and various other pathologies. How specific cellular environments modulate the aggregation of disease proteins is not well understood. Here, we investigated how the endoplasmic reticulum (ER) quality control system handles ß-sheet proteins that were designed de novo to form amyloid-like fibrils. While these proteins undergo toxic aggregation in the cytosol, we find that targeting them to the ER (ER-ß) strongly reduces their toxicity. ER-ß is retained within the ER in a soluble, polymeric state, despite reaching very high concentrations exceeding those of ER-resident molecular chaperones. ER-ß is not removed by ER-associated degradation (ERAD) but interferes with ERAD of other proteins. These findings demonstrate a remarkable capacity of the ER to prevent the formation of insoluble ß-aggregates and the secretion of potentially toxic protein species. Our results also suggest a generic mechanism by which proteins with exposed ß-sheet structure in the ER interfere with proteostasis.

The endoplasmic reticulum: A hub of protein quality control in health and disease.

One third of the eukaryotic proteome is synthesized at the endoplasmic reticulum (ER), whose unique properties provide a folding environment substantially different from the cytosol. A healthy, balanced proteome in the ER is maintained by a network of factors referred to as the ER quality control (ERQC) machinery. This network consists of various protein folding chaperones and modifying enzymes, and is regulated by stress response pathways that prevent the build-up as well as the secretion of potentially toxic and aggregation-prone misfolded protein species. Here, we describe the components of the ERQC machinery, investigate their response to different forms of stress, and discuss the consequences of ERQC break-down.

Failure of RQC machinery causes protein aggregation and proteotoxic stress.

Translation of messenger RNAs lacking a stop codon results in the addition of a carboxy-terminal poly-lysine tract to the nascent polypeptide, causing ribosome stalling. Non-stop proteins and other stalled nascent chains are recognized by the ribosome quality control (RQC) machinery and targeted for proteasomal degradation. Failure of this process leads to neurodegeneration by unknown mechanisms. Here we show that deletion of the E3 ubiquitin ligase Ltn1p in yeast, a key RQC component, causes stalled proteins to form detergent-resistant aggregates and inclusions. Aggregation is dependent on a C-terminal alanine/threonine tail that is added to stalled polypeptides by the RQC component, Rqc2p. Formation of inclusions additionally requires the poly-lysine tract present in non-stop proteins. The aggregates sequester multiple cytosolic chaperones and thereby interfere with general protein quality control pathways. These findings can explain the proteotoxicity of ribosome-stalled polypeptides and demonstrate the essential role of the RQC in maintaining proteostasis.

Downregulation of Fas activity rescues early onset of diabetes in c-Kit(Wv/+) mice.

c-Kit and its ligand stem cell factor (SCF) are important for ß-cell survival and maturation; meanwhile, interactions between the Fas receptor (Fas) and Fas ligand are capable of triggering ß-cell apoptosis. Disruption of c-Kit signaling leads to severe loss of ß-cell mass and function with upregulation of Fas expression in c-Kit(Wv/+) mouse islets, suggesting that there is a critical balance between c-Kit and Fas activation in ß-cells. In the present study, we investigated the interrelationship between c-Kit and Fas activation that mediates ß-cell survival and function. We generated double mutant, c-Kit(Wv/+);Fas(lpr/lpr) (Wv(-/-)), mice to study the physiological and functional role of Fas with respect to ß-cell function in c-Kit(Wv/+) mice. Isolated islets from these mice and the INS-1 cell line were used. We observed that islets in c-Kit(Wv/+) mice showed a significant increase in ß-cell apoptosis along with upregulated p53 and Fas expression. These results were verified in vitro in INS-1 cells treated with SCF or c-Kit siRNA combined with a p53 inhibitor and Fas siRNA. In vivo, Wv(-/-) mice displayed improved ß-cell function, with significantly enhanced insulin secretion and increased ß-cell mass and proliferation compared with Wv(+/+) mice. This improvement was associated with downregulation of the Fas-mediated caspase-dependent apoptotic pathway and upregulation of the cFlip/NF-κB pathway. These findings demonstrate that a balance between the c-Kit and Fas signaling pathways is critical in the regulation of ß-cell survival and function.

Inhibition of Gsk3ß activity improves ß-cell function in c-KitWv/+ male mice.

Previous studies have shown that the stem cell marker, c-Kit, is involved in glucose homeostasis. We recently reported that c-Kit(Wv/+) male mice displayed the onset of diabetes at 8 weeks of age; however, the mechanisms by which c-Kit regulates ß-cell proliferation and function are unknown. The purpose of this study is to examine if c-Kit(Wv/+) mutation-induced ß-cell dysfunction is associated with downregulation of the phospho-Akt/Gsk3ß pathway in c-Kit(Wv/+) male mice. Histology and cell signaling were examined in C57BL/6J/Kit(Wv/+) (c-Kit(Wv/+)) and wild-type (c-Kit(+/+)) mice using immunofluorescence and western blotting approaches. The Gsk3ß inhibitor, 1-azakenpaullone (1-AKP), was administered to c-Kit(Wv/+) and c-Kit(+/+) mice for 2 weeks, whereby alterations in glucose metabolism were examined and morphometric analyses were performed. A significant reduction in phosphorylated Akt was observed in the islets of c-Kit(Wv/+) mice (P<0.05) along with a decrease in phosphorylated Gsk3ß (P<0.05), and cyclin D1 protein level (P<0.01) when compared with c-Kit(+/+) mice. However, c-Kit(Wv/+) mice that received 1-AKP treatment demonstrated normal fasting blood glucose with significantly improved glucose tolerance. 1-AKP-treated c-Kit(Wv/+) mice also showed increased ß-catenin, cyclin D1 and Pdx-1 levels in islets, demonstrating that inhibition of Gsk3ß activity led to increased ß-cell proliferation and insulin secretion. These data suggest that c-Kit(Wv/+) male mice had alterations in the Akt/Gsk3ß signaling pathway, which lead to ß-cell dysfunction by decreasing Pdx-1 and cyclin D1 levels. Inhibition of Gsk3ß could prevent the onset of diabetes by improving glucose tolerance and ß-cell function.