Potent antibody-dependent cellular cytotoxicity of a V2-specific antibody is not sufficient for protection of macaques against SIV challenge.

Fc-mediated antibody effector functions, such as antibody-dependent cellular cytotoxicity (ADCC), can contribute to the containment HIV-1 replication but whether such activities are sufficient for protection is unclear. We previously identified an antibody to the variable 2 (V2) apex of the HIV-1 Env trimer (PGT145) that potently directs the lysis of SIV-infected cells by NK cells but poorly neutralizes SIV infectivity. To determine if ADCC is sufficient for protection, separate groups of six rhesus macaques were treated with PGT145 or a control antibody (DEN3) by intravenous infusion followed five days later by intrarectal challenge with SIVmac239. Despite high concentrations of PGT145 and potent ADCC activity in plasma on the day of challenge, all animals became infected and viral loads did not differ between the PGT145- and DEN3-treated animals. To determine if PGT145 can protect against a neutralization-sensitive virus, two additional groups of six macaques were treated with PGT145 and DEN3 and challenged with an SIVmac239 variant with a single amino acid change in Env (K180S) that increases PGT145 binding and renders the virus susceptible to neutralization by this antibody. Although there was no difference in virus acquisition, peak and chronic phase viral loads were significantly lower and time to peak viremia was significantly delayed in the PGT145-treated animals compared to the DEN3-treated control animals. Env changes were also selected in the PGT145-treated animals that confer resistance to both neutralization and ADCC. These results show that ADCC is not sufficient for protection by this V2-specific antibody. However, protection may be achieved by increasing the affinity of antibody binding to Env above the threshold required for neutralization.

Methionine Restriction Impairs Degradation of a Protein that Aberrantly Engages the Endoplasmic Reticulum Translocon.

Proteins that persistently engage endoplasmic reticulum (ER) translocons are degraded by multiple translocon quality control (TQC) mechanisms. In Saccharomyces cerevisiae , the model translocon-associated protein Deg1 -Sec62 is subject to ER-associated degradation (ERAD) by the Hrd1 ubiquitin ligase and, to a lesser extent, proteolysis mediated by the Ste24 protease. In a recent screen, we identified nine methionine-biosynthetic genes as candidate TQC regulators. Here, we found methionine restriction impairs Hrd1-independent Deg1 -Sec62 degradation. Beyond revealing methionine as a novel regulator of TQC, our results urge caution when working with laboratory yeast strains with auxotrophic mutations, often presumed not to influence cellular processes under investigation.

Substitutions in Nef That Uncouple Tetherin and SERINC5 Antagonism Impair Simian Immunodeficiency Virus Replication in Primary Rhesus Macaque Lymphocytes.

Most simian immunodeficiency viruses (SIVs) use Nef to counteract restriction by the tetherin proteins of their nonhuman primate hosts. In addition to counteracting tetherin, SIV Nef has a number of other functions, including the downmodulation of CD3, CD4, and major histocompatibility complex class I (MHC I) molecules from the surface of SIV-infected cells and the enhancement of viral infectivity by preventing the incorporation of SERINC5 into virions. Although these activities require different surfaces of Nef, they can be difficult to separate because of their dependence on similar interactions with AP-1 or AP-2 for clathrin-mediated endocytosis. We previously observed extensive overlap of the SIV Nef residues required for counteracting tetherin and SERINC5. Here, we define substitutions in Nef that separate anti-tetherin activity from SERINC5 antagonism and other activities of Nef. This information was used to engineer an infectious molecular clone of SIV (SIVmac239nefSA) that is sensitive to tetherin but retains CD3, CD4, MHC I, and SERINC5 downmodulation. In primary rhesus macaque CD4+ T cells, SIVmac239nefSA exhibits impaired replication compared to wild-type SIVmac239 under conditions of interferon-induced upregulation of tetherin. These results demonstrate that tetherin antagonism can be separated from other Nef functions and that resistance to tetherin is essential for optimal replication in primary CD4+ T cells. IMPORTANCE Tetherin is an interferon-inducible transmembrane protein that prevents the detachment of enveloped viruses from infected cells by physically tethering nascent virions to cellular membranes. SIV Nef downmodulates simian tetherin to overcome this restriction in nonhuman primate hosts. Nef also enhances virus infectivity by preventing the incorporation of SERINC5 into virions and contributes to immune evasion by downmodulating other proteins from the cell surface. To assess the contribution of tetherin antagonism to virus replication, we engineered an infectious molecular clone of SIV with substitutions in Nef that uncouple tetherin antagonism from other Nef functions. These substitutions impaired virus replication in interferon-treated macaque CD4+ T cells, revealing the impact of tetherin on SIV replication under physiological conditions in primary CD4+ lymphocytes.

Endoplasmic reticulum stress differentially inhibits endoplasmic reticulum and inner nuclear membrane protein quality control degradation pathways.

Endoplasmic reticulum (ER) stress occurs when the abundance of unfolded proteins in the ER exceeds the capacity of the folding machinery. Despite the expanding cadre of characterized cellular adaptations to ER stress, knowledge of the effects of ER stress on cellular physiology remains incomplete. We investigated the impact of ER stress on ER and inner nuclear membrane protein quality control mechanisms in Saccharomyces cerevisiae. We analyzed the turnover of substrates of four ubiquitin ligases (Doa10, Rkr1/Ltn1, Hrd1, and the Asi complex) and the metalloprotease Ste24 in induced models of ER stress. ER stress did not substantially impact Doa10 or Rkr1 substrates. However, Hrd1-mediated destruction of a protein that aberrantly engages the translocon (Deg1-Sec62) and substrates with luminal degradation signals was markedly impaired by ER stress; by contrast, Hrd1-dependent degradation of proteins with intramembrane degrons was largely unperturbed by ER stress. ER stress impaired the degradation of one of two Asi substrates analyzed and caused a translocon-clogging Ste24 substrate to accumulate in a form consistent with persistent translocon occupation. Degradation of Deg1-Sec62 in the absence of stress and stabilization during ER stress were independent of four ER stress-sensing pathways. Our results indicate ER stress differentially impacts degradation of protein quality control substrates, including those mediated by the same ubiquitin ligase. These observations suggest the existence of additional regulatory mechanisms dictating substrate selection during ER stress.

The effects of varus or valgus malalignment of proximal ulnar fractures on forearm rotation.

INTRODUCTION: Proximal ulna fractures can cause a significant loss of forearm rotation, elbow stiffness, and disability. The objective of this study was to quantify the loss of forearm rotation after simulated varus and valgus malunions of the proximal ulna. METHODS: Eight cadaveric upper extremities were used to quantify loss of forearm rotation after simulation of varus and valgus malunions of the proximal ulna. Maximum supination and pronation were measured at low, medium, and high torque values of 27, 68, and 136 N cm using a custom testing system for the intact specimen and for simulated varus and valgus malunions of the ulna of 5, 10, and 15 degrees. Repeated measures analysis of variance and a Tukey post hoc test with a P value of 0.05 were used for statistical analysis. RESULTS: A statistically significant loss of pronation and total arc of motion compared with the intact state was found with varus deformities of 10 and 15 degrees for the low and middle forearm rotational torque values (P < 0.01 for all comparisons). For the higher torque, a statistically significant difference was found in a loss of pronation in 15-degree varus deformity (P < 0.0001). A statistically significant loss of supination and total arc of motion when compared to the intact state was seen at valgus deformities of 15 degrees for all values of applied torque (P < 0.001 for all comparisons). CONCLUSIONS: Proximal ulna varus and valgus malunions lead to a significant loss of forearm pronation, supination, and total arc of motion. Valgus deformities lead to a loss of supination, whereas varus deformities lead to a greater loss of pronation.

Anatomy and histology of the transverse humeral ligament.

The classic literature describes the transverse humeral ligament (THL) as a distinct anatomic structure with a role in biceps tendon stability; however, recent literature suggests that it is not a distinct anatomic structure. The purpose of this study was to evaluate the gross and microscopic anatomy of the THL, including a specific investigation of the histology of this ligament. Thirty frozen, embalmed cadaveric specimens were dissected to determine the gross anatomy of the THL. Seven specimens were evaluated histologically for the presence of mechanoreceptors and free nerve endings. Two tissue layers were identified in the area described as the THL. In the deep layer, fibers of the subscapularis tendon were found to span the bicipital groove with contributions from the coracohumeral ligament and the supraspinatus tendon. Superficial to this layer was a fibrous fascial covering consisting of distinct bands of tissue. Neurohistology staining revealed the presence of free nerve endings but no mechanoreceptors. This study's findings demonstrate that the THL is a distinct structure continuous with the rotator cuff tendons and the coracohumeral ligament. The finding of free nerve endings in the THL suggests a potential role as a shoulder pain generator.

Blood transfusion associated with shoulder arthroplasty.

BACKGROUND: Studies have reported high rates of transfusion in shoulder arthroplasty. This study was conducted to evaluate the rate of transfusion at our institution, to confirm reported risk factors for transfusion, and to look for changes over time.We hypothesized that transfusion rates associated with shoulder arthroplasty at our institution are lower than those recently reported and that the incidence of transfusion is higher in individuals with low preoperative hemoglobin, with revision arthroplasty, and in older individuals. MATERIALS AND METHODS: A retrospective review of 366 shoulder arthroplasties (323 patients) was performed. This included total shoulder arthroplasties, hemiarthroplasties, revision arthroplasties, and reverse total shoulder arthroplasties. Logistic regression analysis evaluated the association of clinical variables with transfusion. Early (1996-2005) and late (2006-2009) groups were compared to evaluate changes in demographics and transfusion rates over time. RESULTS: The overall transfusion rate was 7.4% (27 of 339). Predictors of transfusion were higher intraoperative blood loss, low preoperative hemoglobin level, and humeral cement fixation. Procedure type was not predictive of transfusion. There was no difference in transfusion rates between the early and late groups, but the late group had an increased use of general anesthesia combined with a regional block, increased intraoperative blood loss, and increased use of sequential compression devices for venous thromboembolism prophylaxis. CONCLUSIONS: Lower preoperative hemoglobin, higher intraoperative blood loss, and humeral cement fixation were predictors of transfusion, but not female sex, increasing age, type of procedure, or comorbidities.

Evaluation of muscle size and fatty infiltration with MRI nine to eleven years following hamstring harvest for ACL reconstruction.

BACKGROUND: The long-term effect of hamstring tendon harvest for anterior cruciate ligament (ACL) reconstruction on muscle morphology is not well documented. Our hypothesis was that harvest of the hamstring tendons for ACL reconstruction would result in persistent loss of volume and cross-sectional area of the gracilis and semitendinosus muscles. METHODS: Magnetic resonance images were made of both limbs of ten patients nine to eleven years after they had ACL reconstruction with ipsilateral hamstring autograft. The volume of the individual thigh muscles bilaterally was calculated. The peak cross-sectional area and the cross-sectional area 7 cm proximal to the joint line was measured for the gracilis and semitendinosus muscles. Data were evaluated with use of the paired t test and Wilcoxon signed-rank test. The gracilis and semitendinosus muscles on the operatively treated side were evaluated for fatty infiltration and tendon regeneration. RESULTS: The mean volume on the operatively treated side was 54.2% of that on the noninvolved side for the gracilis muscle and 58.5% for the semitendinosus muscle. A 7% decrease in quadriceps volume and an 8% increase in the volume of the long head of the biceps on the operatively treated extremity were noted. The semimembranosus muscle and short head of the biceps muscle showed no difference in volume. The gracilis and semitendinosus muscles also showed a decrease in peak cross-sectional area, a decrease in the cross-sectional area 7 cm proximal to the joint line, and evidence of fatty infiltration. There was variable evidence of tendon or scar formation within the tendon bed, with most patients having some tissue that blended into either the sartorius muscle or medial gastrocnemius fascia at a level proximal to the joint line. CONCLUSIONS: At nine to eleven years after ACL reconstruction with ipsilateral hamstring autograft, the gracilis and semitendinosus muscles showed persistent atrophy on the operatively treated side with evidence of fatty infiltration and variability in tendon regeneration. There was also persistent atrophy of the quadriceps muscles and compensatory hypertrophy of the long head of the biceps. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Does landmark selection affect the reliability of tibial tubercle-trochlear groove measurements using MRI?

BACKGROUND: A lateralized tibial tubercle is one potential cause of patellar instability. The tibial tubercle-trochlear groove (TT-TG) distance using CT is a reliable measure and considered the gold standard. Using MRI for this purpose has increased, although the reliability of doing so is not well studied. QUESTIONS/PURPOSES: We sought to (1) determine variability in the insertion of the patellar tendon relative to the tibial tubercle and whether this affects the measurement on MRI of the traditional TT-TG distance versus the functional patellar tendon-trochlear groove (PT-TG) distance, (2) determine the reliability of measuring the osseous TT-TG distance, (3) determine the reliability of measuring the soft tissue PT-TG distance, and (4) compare the reliabilities of using osseous (TT-TG) versus soft tissue (PT-TG) landmarks. METHODS: Four observers measured the TT-TG and the PT-TG distances of 50 MR images of knees obtained for any reason. Each observer repeated these measurements 30 days later. The interobserver and intraobserver reliabilities, measurements per observer that varied from the group mean by greater than 2 mm, and the limit of agreement were calculated. RESULTS: The TT-TG and PT-TG differed by as little as 0.11 mm and by as much as 4.18 mm with an average difference of 1.37 mm. The interobserver and intraobserver reliabilities were greater than 90% for the PT-TG and TT-TG distances. The PT-TG distance was less variable in that this measurement showed interobserver and intraobserver reliabilities of 0.977 and 0.972 respectively, versus 0.913 and 0.961 for the TT-TG measurement. Additionally, the PT-TG measurements resulted in a lower average difference to the mean for each observer, less number of knees per observer where the difference to the mean was greater than 2 mm, and improved limit of agreement. CONCLUSIONS: The TT-TG and the PT-TG distances were not identical and differed by as much as 4.18 mm; as such they are not interchangeable when measuring this distance. Both methods are reliable for measuring lateral offset of the extensor mechanism, but the use of soft tissue landmarks is less variable and thus would provide a more reliable measurement for surgical planning. LEVEL OF EVIDENCE: Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.