Quadriceps muscle atrophy after non-invasive anterior cruciate ligament injury: evidence linking to autophagy and mitophagy

Introduction: Anterior cruciate ligament (ACL) injury is frequently accompanied by quadriceps muscle atrophy, a process closely linked to mitochondrial health and mitochondria-specific autophagy. However, the temporal progression of key quadricep atrophy-mediating events following ACL injury remains poorly understood. To advance our understanding, we conducted a longitudinal study to elucidate key parameters in quadriceps autophagy and mitophagy. Methods: Long-Evans rats were euthanized at 7, 14, 28, and 56 days after non-invasive ACL injury that was induced via tibial compression overload; controls were not injured. Vastus lateralis muscle was extracted, and subsequent immunoblotting analysis was conducted using primary antibodies targeting key proteins involved in autophagy and mitophagy cellular processes. Results: Our findings demonstrated dynamic changes in autophagy and mitophagy markers in the quadriceps muscle during the recovery period after ACL injury. The early response to the injury was characterized by the induction of autophagy at 14 days (Beclin1), indicating an initial cellular response to the injury. Subsequently, at 14 days we observed increase in the elongation of autophagosomes (Atg4B), suggesting a potential remodeling process. The autophagosome flux was also augmented between 14- and 28 days (LC3-II/LC3-I ratio and p62). Notably, at 56 days, markers associated with the elimination of damaged mitochondria were elevated (PINK1, Parkin, and VDAC1), indicating a possible ongoing cellular repair and restoration process. Conclusion: These data highlight the complexity of muscle recovery after ACL injury and underscore the overlooked but crucial role of autophagy and mitophagy in promoting the recovery process.

215 Awardee Talk: Astaxanthin Supplementation During Deconditioning and Reconditioning Periods Reduces Oxidative Stress in Circulation in Polo Ponies

Oxidative status is impacted by fitness and dietary nutrients, such as antioxidants. We hypothesized that astaxanthin (ASTX) supplementation would improve oxidative status in the circulation and muscle in response to exercise following deconditioning and reconditioning in horses. Twelve conditioned polo ponies (14.8 ± 1.7 yr) were assigned to control (CON; n = 6) or astaxanthin supplemented (ASTX; n = 6; 75 mg ASTX daily) groups. Horses performed 26 min submaximal exercise tests (SET) followed by 30 min of recovery while in condition (SET1), after 16 wk of deconditioning (SET2), and after 16 wk of reconditioning (SET3). Blood samples were collected 30 min before and 0, 15, 30, and 60 min after each SET. Semitendinosus muscle biopsies were collected 2 wk before and 2 hr after each SET. Using commercially available kits, plasma and muscle superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities and plasma malondialdehyde (MDA) concentrations were determined. At SET2, ASTX had 116% greater plasma SOD activities than CON (P=0.001). Both treatment groups increased from SET2 to SET3 (P< 0.001), but there were no treatment effects at SET3 (P=0.788). At SET2, plasma GPX activities were 49.3% greater in ASTX than CON (P=0.012), and ASTX tended to be 21.2% greater than CON at SET3 (P=0.096). Plasma MDA concentrations were 22.2% greater in CON than ASTX at SET2 (P=0.034), but not at SET1 or SET3 (P≥0.449). There were no detectable differences in muscle SOD or GPX activities 2 wk before or 2 hr after any SET (P≥0.309). In conclusion, ASTX supplementation maintained circulating antioxidant capacity and minimized oxidant activities during deconditioning, reducing oxidative stress in response to the SET in the circulation but not in the skeletal muscle. This may enable horses to adjust to strenuous exercise more efficiently, improving athletic performance, especially when they are re-introduced to exercise after deconditioning.

Long-Lasting Impairments in Quadriceps Mitochondrial Health, Muscle Size, and Phenotypic Composition Are Present After Non-invasive Anterior Cruciate Ligament Injury

Introduction

Despite rigorous rehabilitation aimed at restoring muscle health, anterior cruciate ligament (ACL) injury is often hallmarked by significant long-term quadriceps muscle weakness. Derangements in mitochondrial function are a common feature of various atrophying conditions, yet it is unclear to what extent mitochondria are involved in the detrimental sequela of quadriceps dysfunction after ACL injury. Using a preclinical, non-invasive ACL injury rodent model, our objective was to explore the direct effect of an isolated ACL injury on mitochondrial function, muscle atrophy, and muscle phenotypic transitions.

Methods

A total of 40 male and female, Long Evans rats (16-week-old) were exposed to non-invasive ACL injury, while 8 additional rats served as controls. Rats were euthanized at 3, 7, 14, 28, and 56 days after ACL injury, and vastus lateralis muscles were extracted to measure the mitochondrial respiratory control ratio (RCR; state 3 respiration/state 4 respiration), mitochondrial reactive oxygen species (ROS) production, fiber cross sectional area (CSA), and fiber phenotyping. Alterations in mitochondrial function and ROS production were detected using two-way (sex:group) analyses of variance. To determine if mitochondrial characteristics were related to fiber atrophy, individual linear mixed effect models were run by sex.

Results

Mitochondria-derived ROS increased from days 7 to 56 after ACL injury (30–100%, P < 0.05), concomitant with a twofold reduction in RCR (P < 0.05). Post-injury, male rats displayed decreases in fiber CSA (days 7, 14, 56; P < 0.05), loss of IIa fibers (day 7; P < 0.05), and an increase in IIb fibers (day 7; P < 0.05), while females displayed no changes in CSA or phenotyping (P > 0.05). Males displayed a positive relationship between state 3 respiration and CSA at days 14 and 56 (P < 0.05), while females only displayed a similar trend at day 14 (P = 0.05).

Conclusion

Long-lasting impairments in quadriceps mitochondrial health are present after ACL injury and play a key role in the dysregulation of quadriceps muscle size and composition. Our preclinical data indicate that using mitoprotective therapies may be a potential therapeutic strategy to mitigate alterations in muscle size and characteristic after ACL injury.

Association of Condylar Bone Quality with TMJ Osteoarthritis

The etiology and treatment of temporomandibular joint (TMJ) osteoarthritis (TMJOA) remain complex and unclear. Based on clinical observations, we hypothesized that low condylar bone quality is significantly correlated with TMJOA and explored this association in a cross-sectional study with human patients. A total of 254 postmenopausal female participants were included in this study. Radiographic findings from cone beam computed tomography (CBCT) and clinical symptoms were used to classify each TMJ data sample as healthy control ( n = 124) or TMJOA ( n = 130). Condylar bone mineral density (BMD) (computed tomography Hounsfield unit [CT HU]) and bone volume fraction (BV/TV) were measured and modeled as predictors of healthy control versus TMJOA status in multilevel logistic regression analyses. Both CT HU (adjusted odds ratio [AOR] = 0.9989, interquartile odds ratio [IOR] = 0.4206) and BV/TV (AOR= 0.8096, IOR = 0.1769) were negatively associated with TMJOA ( P = 0.049, 0.011, respectively). To assess the diagnostic performance of CT HU and BV/TV for identification of TMJOA, receiver operating characteristic (ROC) curves were plotted. The estimated areas under the curve (AUC) were 0.6622 for BV/TV alone, 0.6074 for CT HU alone, and 0.7136 for CT HU and BV/TV together. The model incorporating CT HU and BV/TV together had a significantly higher AUC than the models using BV/TV alone ( P = 0.038) or HU alone ( P = 0.021). In conclusion, we found that low condylar bone quality was significantly correlated with TMJOA development and that condylar CT HU and BV/TV can be used together as a potential diagnostic tool for TMJOA. Careful clinical evaluation of the condyle coupled with appropriate radiographic interpretation would thus be critical for the early detection of TMJOA.

Idiopathic adhesive capsulitis. A prospective functional outcome study of nonoperative treatment

BACKGROUND

Idiopathic adhesive capsulitis is a commonly recognized but poorly understood cause of a painful and stiff shoulder. Although most orthopaedic literature supports treatment with physical therapy and stretching exercises, some studies have demonstrated late pain and functional deficits. The purpose of this study was to evaluate the outcome of patients with idiopathic adhesive capsulitis who were treated with a stretching-exercise program.

METHODS

Seventy-five consecutive patients (seventy-seven shoulders) with phase-II idiopathic adhesive capsulitis were treated with use of a specific four-direction shoulder-stretching exercise program and evaluated prospectively. The initial evaluation included the recording of a detailed medical and orthopaedic history and assessment of pain, range of motion, and function. The outcome evaluation included assessment of pain, range of motion, and function; completion of the Disabilities of the Arm, Shoulder, and Hand (DASH) Questionnaire; and completion of the Short Form-36 (SF-36) Health Survey. The mean duration of follow-up was twenty-two months (range, twelve to forty-one months). One patient died prior to the final evaluation, and three patients were lost to follow-up.

RESULTS

Sixty-four (90 percent) of the patients reported a satisfactory outcome. Seven (10 percent) were not satisfied with the outcome, and five (7 percent) underwent manipulation and/or arthroscopic capsular release. The outcomes of the patients who did not have manipulation or capsular release were evaluated. There were significant improvements in the scores for pain at rest (from a mean of 1.57 points before treatment to a mean of 1.16 points at the final evaluation; p < 0.001) and pain with activity (from a mean of 4.12 points before treatment to a mean of 1.33 points at the final evaluation; p < 0.0001). On the average, active forward elevation increased 43 degrees, active external rotation increased 25 degrees, passive internal rotation increased eight vertebral levels, and the glenohumeral rotation arc at 90 degrees of abduction increased 72 degrees (p < 0.00001). The number of "yes" responses to the Simple Shoulder Test increased from a mean of 4.1 (of a possible twelve) to a mean of 10.75 (p < 0.00001). Despite the significant improvements and the high rate of patient satisfaction, there were still significant differences in the pain and motion of the affected shoulder when compared with those of the unaffected, contralateral shoulder (p < 0.00001). At the final outcome evaluation, the DASH scores demonstrated limitations when compared with known population norms, whereas the profiles of the SF-36 were comparable with those of age and gender-matched control populations. Prior treatment with physical therapy and a Workers' Compensation claim or pending litigation were the only variables that were associated with the eventual need for manipulation or capsular release. Male gender and diabetes mellitus were associated with worse motion at the final evaluation. Patients with a greater severity of pain with activity at the initial evaluation had significantly lower DASH scores at the final evaluation, and patients with lower initial scores on the Simple Shoulder Test had comparatively lower scores on the Simple Shoulder Test at the outcome evaluation.

CONCLUSIONS

The vast majority of patients who have phase-II idiopathic adhesive capsulitis can be successfully treated with a specific four-direction shoulder-stretching exercise program. Although measurable limitations and deficiencies were noted at the outcome evaluation, these appeared to be acceptable to most of the patients and did not affect their general health status. Patients with more severe pain and functional limitations before treatment had relatively worse outcomes. More aggressive treatment such as manipulation or capsular release was rarely necessary, and the efficacy of early use of these treatments should be further studied.

Formation and characterization of the trimeric form of the fusion protein of Semliki Forest Virus

Enveloped animal viruses infect cells via fusion of the viral membrane with a host cell membrane. Fusion is mediated by a viral envelope glycoprotein, which for a number of enveloped animal viruses rearranges itself during fusion to form a trimeric alpha-helical coiled-coil structure. This conformational change from the metastable, nonfusogenic form of the spike protein to the highly stable form involved in fusion can be induced by physiological activators of virus fusion and also by a variety of destabilizing conditions. The E1 spike protein subunit of Semliki Forest virus (SFV) triggers membrane fusion upon exposure to mildly acidic pH and forms a homotrimer that appears necessary for fusion. We have here demonstrated that formation of the E1 homotrimer was efficiently triggered under low-pH conditions but not by perturbants such as heat or urea, despite their induction of generalized conformational changes in the E1 and E2 subunits and partial exposure of an acid-specific E1 epitope. We used a sensitive fluorescence assay to show that neither heat nor urea treatment triggered SFV-liposome fusion at neutral pH, although either treatment inactivated subsequent low-pH-triggered fusion activity. Once formed, the low-pH-induced E1 homotrimer was very stable and was only dissociated under harsh conditions such as heating in sodium dodecyl sulfate. Taken together, these data, as well as protein structure predictions, suggest a model in which the less stable native E1 subunit specifically responds to low pH to form the more stable E1 homotrimer via conformational changes different from those of the coiled-coil type of fusion proteins.

An epitope of the Semliki Forest virus fusion protein exposed during virus-membrane fusion

Semliki Forest virus (SFV) is an enveloped alphavirus that infects cells via a membrane fusion reaction triggered by acidic pH in the endocytic pathway. Fusion is mediated by the spike protein E1 subunit, an integral membrane protein that contains the viral fusion peptide and forms a stable homotrimer during fusion. We have characterized four monoclonal antibodies (MAbs) specific for the acid conformation of E1. These MAbs did not inhibit fusion, suggesting that they bind to an E1 region different from the fusion peptide. Competition analyses demonstrated that all four MAbs bound to spatially related sites on acid-treated virions or isolated spike proteins. To map the binding site, we selected for virus mutants resistant to one of the MAbs, E1a-1. One virus isolate, SFV 4-2, showed reduced binding of three acid-specific MAbs including E1a-1, while its binding of one acid-specific MAb as well as non-acid-specific MAbs to E1 and E2 was unchanged. The SFV 4-2 mutant was fully infectious, formed the E1 homotrimer, and had the wild-type pH dependence of infection. Sequence analysis demonstrated that the relevant mutation in SFV 4-2 was a change of E1 glycine 157 to arginine (G157R). Decreased binding of MAb E1a-1 was observed under a wide range of assay conditions, strongly suggesting that the E1 G157R mutation directly affects the MAb binding site. These data thus localize an E1 region that is normally hidden in the neutral pH structure and becomes exposed as part of the reorganization of the spike protein to its fusion-active conformation.

Growth and stability of a cholesterol-independent Semliki Forest virus mutant in mosquitoes

Semliki Forest virus (SFV) is an enveloped alphavirus that is transmitted in the wild by mosquito vectors. In tissue culture cells, SFV requires cholesterol in the cell membrane both for virus membrane fusion and for the efficient exit of progeny virus from the cell. A previously isolated SFV mutant, srf-3, is strikingly less cholesterol-dependent for virus fusion, exit, and growth due to a single amino acid change in the E1 spike protein subunit, proline 226 to serine. Here we show that when mosquitoes were infected by intrathoracic injection at a range of virus multiplicities, the growth of srf-3 was significantly more rapid than that of wild-type virus, particularly at low multiplicity infection. The differential cholesterol requirements for wild-type and srf-3 infection were maintained during virus passage through mosquitoes. The presence or absence of cholesterol in the srf-3 virus membrane did not affect its infection properties in mosquitoes. Thus the srf-3 mutation causes a growth advantage in the tissues of the mosquito host.

Static forces and moments generated in the insect leg: comparison of a three-dimensional musculo-skeletal computer model with experimental measurements

As a first step towards the integration of information on neural control, biomechanics and isolated muscle function, we constructed a three-dimensional musculo-skeletal model of the hind leg of the death-head cockroach Blaberus discoidalis. We tested the model by measuring the maximum force generated in vivo by the hind leg of the cockroach, the coxa&shy;femur joint angle and the position of this leg during a behavior, wedging, that was likely to require maximum torque or moment production. The product of the maximum force of the leg and its moment arm yielded a measured coxa&shy;femur joint moment for wedging behavior. The maximum musculo-apodeme moment predicted by summing all extensor muscle moments in the model was adequate to explain the magnitude of the coxa&shy;femur joint moment produced in vivo by the cockroach and occurred at the same joint angle measured during wedging. Active isometric muscle forces predicted from our model varied by 3.5-fold among muscles and by as much as 70 % with joint angle. Sums of active and passive forces varied by less than 3.5 % over the entire range of possible joint angles (0&shy;125 &deg;). Maximum musculo-apodeme moment arms varied nearly twofold among muscles. Moment arm lengths decreased to zero and switched to the opposite side of the center of rotation at joint angles within the normal range of motion. At large joint angles (&gt;100 &deg;), extensors acted as flexors. The effective mechanical advantage (musculo-apodeme moment arm/leg moment arm = 0.10) resulted in the six femoral extensor muscles of the model developing a summed force (1.4 N) equal to over 50 times the body weight. The model's three major force-producing extensor muscles attained 95 % of their maximum force, moment arm and moment at the joint angle used by the animal during wedging.

Intrastriatal injections of quinolinic acid or kainic acid: differential patterns of cell survival and the effects of data analysis on outcome

There is controversy about the extent to which lesions of the rat striatum with excitatory amino acids mimic the cellular pathology seen in Huntington's Disease (HD). We sought to resolve this debate by determining with cell counts in adjacent sections the patterns of survival of medium spiny and aspiny striatal neurons using enkephalin immunohistochemistry and NADPH-diaphorase histochemistry as markers of these cell populations, respectively. Results showed that 2 weeks after quinolinic acid lesions, cell loss was qualitatively similar for the two cell groups. However, by varying the size of the sampling area for quantitative analyses and its distance from the lesion zone, the outcome of the statistical analyses varied enormously. Thus, a relative sparing of NADPH-diaphorase-labeled cells compared to enkephalin-labeled cells could be detected quantitatively in transition areas bordering the lesion under some but not all analytical conditions. Kainic acid lesions depleted both cell populations similarly, except in regions of transition farthest from the lesion, where enkephalin-containing neurons were more resistant than NADPH-diaphorase-containing cells. The size of the transition area around the lesion also differed depending upon excitotoxin and cell population. These results help to reconcile the controversy and suggest that with highly specified quantitative conditions quinolinic acid-induced injury of the striatum can resemble the histopathology of HD.