Improving Medical Student Mentorship in Orthopaedic Surgery.

Introduction: Owing to limited clinical clerkships and travel restrictions related to COVID-19, recent medical student mentorship in orthopaedic surgery has been impacted negatively. The purpose of this quality improvement (QI) project was to determine if medical student awareness of orthopaedics as a possible career field may be improved through a mentoring program designed and delivered by orthopaedic residents. Methods: A five-resident QI team developed four educational sessions aimed at a medical student audience. Forum topics included: (1) orthopaedics as a career, (2) fracture conference, (3) splinting workshop, and (4) residency application process. Pre- and post-forum surveys were administered to student participants to assess changes in their perceptions regarding orthopaedic surgery. Data derived from the questionnaires were analyzed with nonparametric statistical tests. Results: Of 18 forum participants, 14 were men and 4 were women. A total of 40 survey pairs were collected, averaging 10 per session. In the all-participant encounter analysis, there were statistically significant improvements in all outcome measures including interest in, exposure to, and knowledge of orthopaedics; exposure to our training program; and ability to interact with our residents. Those undecided regarding their specialty demonstrated larger increases in post-forum responses, suggesting that the learning experience was more impactful for that subgroup. Conclusions: This QI initiative was a successful demonstration of orthopaedic resident mentorship of medical students, wherein perceptions of orthopaedics were influenced favorably by the educational experience. For some students with limited access to orthopaedic clerkships or formal one-on-one mentoring, forums like these may be an acceptable alternative.

Sex-Based Differences in Outcomes After Hip Arthroscopic Surgery for Femoroacetabular Impingement: A Systematic Review.

Background: While sex-based differences in outcomes after hip arthroscopic surgery for femoroacetabular impingement syndrome (FAIS) are often recorded, no studies have been dedicated to analyzing the literature as a whole. Purpose: To investigate whether sex is a predictor of outcomes in studies evaluating hip arthroscopic surgery for FAIS. Study Design: Systematic review; Level of evidence, 4. Methods: A systematic review was conducted following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We searched the PubMed, Embase, Cochrane, Ovid, and PubMed Central databases for English-language studies that evaluated sex-specific outcomes in human populations. The search terms used were as follows: ("Hip Arthroscopy") AND ("Femoroacetabular Impingement" OR "FAI") AND ("Sex" OR "Gender" OR "Male" OR "Female"). Studies with evidence levels 2 through 4 were included. The studies were then screened, followed by data extraction. Modified Harris Hip Score (mHHS) outcomes and return-to-sport (RTS) rates were recorded. These were analyzed using random-effects meta-analysis. Heterogeneity was calculated using the I 2 statistic. Results: Of 256 full-text articles screened, 48 articles were included in this analysis; of these, 14 studies (29%) concluded that female sex was a negative predictor of postoperative outcomes, while 6 studies (13%) found female sex to be positive predictor. The remaining 28 studies (58%) found no sex-based differences in postoperative outcomes. Of 7 studies (416 male and 519 female) included in the mHHS analysis, 2 studies concluded that male patients had significantly higher postoperative mHHS scores. Of 6 studies (502 male and 396 female) included in the RTS analysis, 1 study concluded that male patients had a significantly higher RTS rate. Conclusion: Almost one-third of the included studies determined that female sex was a negative predictor of postoperative outcomes, 13% found female sex to be a positive predictor, and 58% found no sex-based differences. Our study illustrates an insufficiency of high-level evidence supporting sex-specific differences in outcomes after hip arthroscopic surgery, but findings indicated that the postoperative mHHS score and RTS rate may be influenced by sex.

Comparison between mouse and sea urchin orthologs of voltage-gated proton channel suggests role of S3 segment in activation gating.

The voltage-gated proton channel, Hv1, is expressed in blood cells, airway epithelium, sperm and microglia, playing important roles in diverse biological contexts including phagocytosis or sperm maturation through its regulation of membrane potential and pH. The gene encoding Hv1, HVCN1, is widely found across many species and is also conserved in unicellular organisms such as algae or dinoflagellates where Hv1 plays role in calcification or bioluminescence. Voltage-gated proton channels exhibit a large variation of activation rate among different species. Here we identify an Hv1 ortholog from sea urchin, Strongylocentrotus purpuratus, SpHv1. SpHv1 retains most of key properties of Hv1 but exhibits 20-60 times more rapid activation kinetics than mammalian orthologs upon heterologous expression in HEK293T cells. Comparison between SpHv1 and mHv1 highlights novel roles of the third transmembrane segment S3 in activation gating of Hv1.

Rapid desensitization of the rat α7 nAChR is facilitated by the presence of a proline residue in the outer ß-sheet.

The rat α7 nicotinic acetylcholine receptor (nAChR) has a proline residue near the middle of the ß9 strand. The replacement of this proline residue at position 180 (P180) by either threonine (α7-P180T) or serine (α7-P180S) slowed the onset of desensitization dramatically, with half-times of ~930 and 700 ms, respectively, compared to 90 ms for the wild-type receptor. To investigate the importance of the hydroxyl group on the position 180 side-chains, the mutant receptors α7-P180Y and α7-P180F were studied and showed half-times of desensitization of 650 and 160 ms, respectively. While a position 180 side-chain OH group may contribute to the slow desensitization rates, α7-P180S and α7-P180V resulted in receptors with similar desensitization rates, suggesting that increased backbone to backbone H bonding expected in the absence of proline at position 180 would likely exert a great effect on desensitization. Single channel recordings indicated that for the α7-P180T receptor there was a significantly reduced closed time without any change in single channel conductance (as compared to wild-type). Kinetic simulations indicated that all changes observed for the mutant channel behaviour were reproduced by decreasing the rate of desensitization, and increasing the microscopic affinity to resting receptors. Molecular dynamics (MD) simulations on a homology model were used to provide insight into likely H bond interactions within the outer ß-sheet that occur when the P180 residue is mutated. All mutations analysed increased about twofold the predicted number of H bonds between the residue at position 180 and the backbone of the ß10 strand. Moreover, the α7-P180T and α7-P180S mutations also formed some intrastrand H bonds along the ß9 strand, although H bonding of the OH groups of the threonine or serine side-chains was predicted to be infrequent. Our results indicate that rapid desensitization of the wild-type rat α7 nAChR is facilitated by the presence of the proline residue within the ß9 strand.

Evolution by leaps: gene duplication in bacteria.

BACKGROUND: Sequence related families of genes and proteins are common in bacterial genomes. In Escherichia coli they constitute over half of the genome. The presence of families and superfamilies of proteins suggest a history of gene duplication and divergence during evolution. Genome encoded protein families, their size and functional composition, reflect metabolic potentials of the organisms they are found in. Comparing protein families of different organisms give insight into functional differences and similarities. RESULTS: Equivalent enzyme families with metabolic functions were selected from the genomes of four experimentally characterized bacteria belonging to separate genera. Both similarities and differences were detected in the protein family memberships, with more similarities being detected among the more closely related organisms. Protein family memberships reflected known metabolic characteristics of the organisms. Differences in divergence of functionally characterized enzyme family members accounted for characteristics of taxa known to differ in those biochemical properties and capabilities. While some members of the gene families will have been acquired by lateral exchange and other former family members will have been lost over time, duplication and divergence of genes and functions appear to have been a significant contributor to the functional diversity of today's microbes. CONCLUSIONS: Protein families seem likely to have arisen during evolution by gene duplication and divergence where the gene copies that have been retained are the variants that have led to distinct bacterial physiologies and taxa. Thus divergence of the duplicate enzymes has been a major process in the generation of different kinds of bacteria.

Reversal of agonist selectivity by mutations of conserved amino acids in the binding site of nicotinic acetylcholine receptors.

Homomeric alpha7 and heteromeric alpha4beta2 nicotinic acetylcholine receptors (nAChR) can be distinguished by their pharmacological properties, including agonist specificity. We introduced point mutations of conserved amino acids within the C loop, a region of the receptor critical for agonist binding, and we examined the expression of the mutant receptors in Xenopus oocytes. Mutation of either a conserved C loop tyrosine (188) to phenylalanine or a nearby conserved aspartate (197) to alanine resulted in alpha7 receptors for which the alpha7-selective agonist 3-(4-hydroxy, 2-methoxybenzylidene) anabaseine (4OH-GTS-21) had roughly the same potency as for wild-type receptors, whereas the physiologic agonist acetylcholine (ACh) showed drastically reduced potency for these mutant receptors. Corresponding mutations in alpha4 receptors co-expressed with beta2 resulted in alpha4beta2 receptors for which ACh potency was relatively unchanged, although the efficacy of the alpha7-selective agonist 4OH-GTS-21 was increased greatly relative to that of ACh. We also investigated the significance of a conserved lysine (145 in alpha7), proposed to form a stable salt bridge with Asp-197 in the resting state of the receptor. Mutations of this residue in both alpha7 and alpha4 resulted in receptors that were largely unresponsive to both ACh and 4OH-GTS-21. Our results suggest that initiation of gating depends both on specific interactions between residues in the C loop domain and, depending on receptor subtype, the physiochemical properties of the agonist, so that in the altered environment of the alpha4Y190F-binding site, large hydrophobic benzylidene anabaseines may close the C loop and initiate channel gating more effectively than the polar agonist ACh.

Rhesus monkey alpha7 nicotinic acetylcholine receptors: comparisons to human alpha7 receptors expressed in Xenopus oocytes.

An alpha7 nicotinic acetylcholine receptor sequence was cloned from Rhesus monkey (Macaca mulatta). This clone differs from the mature human alpha7 nicotinic acetylcholine receptor in only four amino acids, two of which are in the extracellular domain. The monkey alpha7 nicotinic receptor was characterized in regard to its functional responses to acetylcholine, choline, cytisine, and the experimental alpha7-selective agonists 4OH-GTS-21, TC-1698, and AR-R17779. For all of these agonists, the EC(50) for activation of monkey receptors was uniformly higher than for human receptors. In contrast, the potencies of mecamylamine and MLA for inhibiting monkey and human alpha7 were comparable. Acetylcholine and 4OH-GTS-21 were used to probe the significance of the single point differences in the extracellular domain. Mutants with the two different amino acids in the extracellular domain of the monkey receptor changed to the corresponding sequence of the human receptor had responses to these agonists that were not significantly different in EC(50) from wild-type human alpha7 nicotinic receptors. Monkey alpha7 nicotinic receptors have a serine at residue 171, while the human receptors have an asparagine at this site. Monkey S171N mutants were more like human alpha7 nicotinic receptors, while mutations at the other site (K186R) had relatively little effect. These experiments point toward the basic utility of the monkey receptor as a model for the human alpha7 nicotinic receptor, albeit with the caveat that these receptors will vary in their agonist concentration dependency. They also point to the potential importance of a newly identified sequence element for modeling the specific amino acids involved with receptor activation.

The structural basis for GTS-21 selectivity between human and rat nicotinic alpha7 receptors.

The alpha7 nAChR-selective partial agonist 3-(2,4-dimethoxybenzylidene)anabaseine (GTS-21) is more efficacious and potent for rat receptors than for human alpha7 receptors. Four single amino acid differences exist between human and rat alpha7 in the agonist binding site, two in the C loop, and one each in the E and F loops. Reciprocal mutations were made in these three domains and evaluated in Xenopus laevis oocytes. Mutations in the C and F loops significantly increased the efficacy of GTS-21 for the human receptor mutants but not to the level of the wild-type, and reciprocal mutations in rat alpha7 did not decrease responses to GTS-21. Whereas mutations in the E loop alone were without effect, the E- and F-loop mutations together increased GTS-21 efficacy and potency for human receptors, but the EF mutations in the rat receptors decreased the GTS-21 potency without changing the efficacy. The only mutants that showed a full reversal of the efficacy differences between human and rat alpha7 contained complete exchange of all four sites in the C, E, and F loops or just the sites in the C and F loops. However, the reversal of the potency ratio seen with the EF mutants was not evident in the CEF mutants. Our data therefore indicate that the pharmacological differences between rat and human alpha7 receptors are caused by reciprocal differences in sites within and around the binding site. Specific features in the agonist molecule itself are also identified that interact with these structural features of the receptor agonist binding site.

Comparison of K+-channel genes within the genomes of Anopheles gambiae and Drosophila melanogaster.

BACKGROUND: Potassium channels are the largest and most diverse type of ion channel found in nature. The completion of the sequencing of the genomes of Drosophila melanogaster and Anopheles gambiae, which belong to the same order, the Diptera, allows us to compare and contrast K+-channel genes and gene families present within the genomes of two dipterans. RESULTS: This study identifies at least eight voltage-gated K+-channel genes in Anopheles, as well as three Slo-family, three Eag-family and six inward rectifier K+-channel genes. The genomic organization of K+-channel genes from Drosophila and Anopheles is well conserved. The sequence identity of the most similar K+-channel gene products between these two species ranges from 42% to 98%, with a mean value of 85%. Although most K+-channel genes in Drosophila and Anopheles are present in a 1:1 ratio, Anopheles has more genes in three K+-channel types, namely KQT, Kv3, and inward rectifier channels. Microsynteny between the genes flanking K+-channel genes in Drosophila and Anopheles was seldom observed; however, most of the K+-channel genes are indeed located at positions which a previous genome-wide comparison has designated as homologous chromosomal regions. CONCLUSIONS: The Anopheles genome encodes more voltage-gated and inward rectifier K+-channel genes than that of Drosophila. Despite the conservation of intron-exon boundaries, orthologs of genes flanking K+-channel genes in Drosophila are generally not found adjacent to the Anopheles K+-channel orthologs, suggesting that extensive translocation of genes has occurred since the divergence of these two organisms.