Identifying characteristics and clinical conditions associated with hand grip strength in adults: the Project Baseline Health Study.

Low hand grip strength (HGS) is associated with several conditions, but its value outside of the older adult population is unclear. We sought to identify the most salient factors associated with HGS from an extensive list of candidate variables while stratifying by age and sex. We used data from the initial visit from the Project Baseline Health Study (N = 2502) which captured detailed demographic, occupational, social, lifestyle, and clinical data. We applied MI-LASSO using group methods to determine variables most associated with HGS out of 175 candidate variables. We performed analyses separately for sex and age (< 65 vs. ≥ 65 years). Race was associated with HGS to varying degrees across groups. Osteoporosis and osteopenia were negatively associated with HGS in female study participants. Immune cell counts were negatively associated with HGS for male participants ≥ 65 (neutrophils) and female participants (≥ 65, monocytes; < 65, lymphocytes). Most findings were age and/or sex group-specific; few were common across all groups. Several of the variables associated with HGS in each group were novel, while others corroborate previous research. Our results support HGS as a useful indicator of a variety of clinical characteristics; however, its utility varies by age and sex.

Structure of mavacamten-free human cardiac thick filaments within the sarcomere by cryoelectron tomography.

Heart muscle has the unique property that it can never rest; all cardiomyocytes contract with each heartbeat which requires a complex control mechanism to regulate cardiac output to physiological requirements. Changes in calcium concentration regulate the thin filament activation. A separate but linked mechanism regulates the thick filament activation, which frees sufficient myosin heads to bind the thin filament, thereby producing the required force. Thick filaments contain additional nonmyosin proteins, myosin-binding protein C and titin, the latter being the protein that transmits applied tension to the thick filament. How these three proteins interact to control thick filament activation is poorly understood. Here, we show using 3-D image reconstruction of frozen-hydrated human cardiac muscle myofibrils lacking exogenous drugs that the thick filament is structured to provide three levels of myosin activation corresponding to the three crowns of myosin heads in each 429Å repeat. In one crown, the myosin heads are almost completely activated and disordered. In another crown, many myosin heads are inactive, ordered into a structure called the interacting heads motif. At the third crown, the myosin heads are ordered into the interacting heads motif, but the stability of that motif is affected by myosin-binding protein C. We think that this hierarchy of control explains many of the effects of length-dependent activation as well as stretch activation in cardiac muscle control.

Characterizing Acute Low Back Pain in a Community-Based Cohort.

Acute low back pain (LBP) is a common experience, however, the associated pain severity, pain frequency, and characteristics of individuals with acute LBP in community settings have yet to be well understood. In this manuscript, three acute LBP severity categorization definitions were used based on LBP frequency combined with either 1) pain impact frequency (impact-based) or 2) pain intensity (intensity-based), as well as LBP pain interference frequency (interference only-based) severity categories. The purpose of this manuscript is to describe and then compare these acute LBP severity groups in the following characteristics: 1) sociodemographic, 2) general and physical health, and 3) psychological. This cross-sectional study used baseline data from 131 community-based participants with acute LBP (<4 weeks duration before screening and ≥30 pain-free days before acute LBP onset). Descriptive associations were calculated as prevalence ratios for categorical variables and Hedges' g for continuous variables. Our analyses identified several large associations for impact-based and intensity-based categories with global mental health, global physical health, STarT Back Screening Tool risk category, and general health. Larger associations were found with social constructs (racially and ethnically minoritized, performance of social roles, and isolation) when using the intensity-based versus impact-based categorization. The interference-based category did not capture as much variability between acute LBP severity categories. This study adds to the literature by providing standard ways to characterize community-based individuals experiencing acute LBP. The robust differences observed between these categorization approaches suggest that how we define acute LBP severity is consequential; these different approaches may be used to improve the early identification of factors potentially contributing to the development of chronic LBP.

Structure of the Drosophila melanogaster Flight Muscle Myosin Filament at 4.7 Å Resolution Reveals New Details of Non-Myosin Proteins.

Striated muscle thick filaments are composed of myosin II and several non-myosin proteins which define the filament length and modify its function. Myosin II has a globular N-terminal motor domain comprising its catalytic and actin-binding activities and a long α-helical, coiled tail that forms the dense filament backbone. Myosin alone polymerizes into filaments of irregular length, but striated muscle thick filaments have defined lengths that, with thin filaments, define the sarcomere structure. The motor domain structure and function are well understood, but the myosin filament backbone is not. Here we report on the structure of the flight muscle thick filaments from Drosophila melanogaster at 4.7 Å resolution, which eliminates previous ambiguities in non-myosin densities. The full proximal S2 region is resolved, as are the connecting densities between the Ig domains of stretchin-klp. The proteins, flightin, and myofilin are resolved in sufficient detail to build an atomic model based on an AlphaFold prediction. Our results suggest a method by which flightin and myofilin cooperate to define the structure of the thick filament and explains a key myosin mutation that affects flightin incorporation. Drosophila is a genetic model organism for which our results can define strategies for functional testing.

The cryo-EM 3D image reconstruction of isolated Lethocerus indicus Z-discs.

The Z-disk of striated muscle defines the ends of the sarcomere, which repeats many times within the muscle fiber. Here we report application of cryoelectron tomography and subtomogram averaging to Z-disks isolated from the flight muscles of the large waterbug Lethocerus indicus. We use high salt solutions to remove the myosin containing filaments and use gelsolin to remove the actin filaments of the A- and I-bands leaving only the thin filaments within the Z-disk which were then frozen for cryoelectron microscopy. The Lethocerus Z-disk structure is similar in many ways to the previously studied Z-disk of the honeybee Apis mellifera. At the corners of the unit cell are positioned trimers of paired antiparallel F-actins defining a large solvent channel, whereas at the trigonal positions are positioned F-actin trimers converging slowly towards their (+) ends defining a small solvent channel through the Z-disk. These near parallel F-actins terminate at different Z-heights within the Z-disk. The two types of solvent channel in Lethocerus are similar in size compared to those of Apis which are very different in size. Two types of α-actinin crosslinks were observed between oppositely oriented actin filaments. In one of these, the α-actinin long axis is almost parallel to the F-actins it crosslinks. In the other, the α-actinins are at a small but distinctive angle with respect to the crosslinked actin filaments. The utility of isolated Z-disks for structure determination is discussed.

Double-headed binding of myosin II to F-actin shows the effect of strain on head structure.

Force production in muscle is achieved through the interaction of myosin and actin. Strong binding states in active muscle are associated with Mg·ADP bound to the active site; release of Mg·ADP allows rebinding of ATP and dissociation from actin. Thus, Mg·ADP binding is positioned for adaptation as a force sensor. Mechanical loads on the lever arm can affect the ability of myosin to release Mg·ADP but exactly how this is done is poorly defined. Here we use F-actin decorated with double-headed smooth muscle myosin fragments in the presence of Mg·ADP to visualize the effect of internally supplied tension on the paired lever arms using cryoEM. The interaction of the paired heads with two adjacent actin subunits is predicted to place one lever arm under positive and the other under negative strain. The converter domain is believed to be the most flexible domain within myosin head. Our results, instead, point to the segment of heavy chain between the essential and regulatory light chains as the location of the largest structural change. Moreover, our results suggest no large changes in the myosin coiled coil tail as the locus of strain relief when both heads bind F-actin. The method would be adaptable to double-headed members of the myosin family. We anticipate that the study of actin-myosin interaction using double-headed fragments enables visualization of domains that are typically noisy in decoration with single-headed fragments.

Probable trauma associated sleep disorder in post-9/11 US Veterans.

Study Objectives: The purpose of this study was to (1) estimate trauma associated sleep disorder (TASD) prevalence among post-9/11 era veterans and to describe differences in service and comorbid mental health clinical characteristics among individuals with and without probable TASD, and (2) estimate TASD prevalence and characteristics of reported traumatic experiences stratified by sex. Methods: We used cross-sectional data from the post-deployment mental health study of post-9/11 veterans, which enrolled and collected baseline data from 2005 to 2018. We classified veterans as having probable TASD using self-reported measures: traumatic experiences from the traumatic life events questionnaire (TLEQ) and items from the Pittsburgh sleep quality index with Addendum for posttraumatic stress disorder (PTSD) mapped to TASD diagnostic criteria and ascertained mental health diagnoses (PTSD, major depressive disorder [MDD]) via Structured Clinical Interview for DSM-IV. We calculated effect sizes as prevalence ratios (PR) for categorical variables and Hedges' g for continuous variables. Results: Our final sample included 3618 veterans (22.7% female). TASD prevalence was 12.1% (95% CI: 11.1% to 13.2%) and sex-stratified prevalence was similar for female and male veterans. Veterans with TASD had a much higher comorbid prevalence of PTSD (PR: 3.72, 95% CI: 3.41 to 4.06) and MDD (PR: 3.93, 95% CI: 3.48 to 4.43). Combat was the highest reported most distressing traumatic experience among veterans with TASD (62.6%). When stratifying by sex, female veterans with TASD had a wider variety of traumatic experiences. Conclusions: Our results support the need for improved screening and evaluation for TASD in veterans, which is currently not performed in routine clinical practice.

John Squire and the myosin thick filament structure in muscle.

The structure of the thin, actin-containing filament of muscle is both highly conserved across a broad range of muscle types and is now well understood. The structure of the thick, myosin-containing filaments of striated muscle are quite variable and remained comparatively unknown until recently, particularly in the arrangement of the myosin tails. John Squire played a major role not only in our understanding of thin filament structure and function but also in the structure of the thick filaments. Long before much was known about the structure and composition of muscle thick filaments, he proposed a general model for how myosin filaments were constructed. His role in our current understanding the structure of striated muscle thick filaments and the extent through which his predictions have held true is the topic of this review.

Nightmares: an independent risk factor for cardiovascular disease?

STUDY OBJECTIVES: Prior work has established associations between post-traumatic stress disorder (PTSD), disrupted sleep, and cardiovascular disease (CVD), but few studies have examined health correlates of nightmares beyond risks conferred by PTSD. This study examined associations between nightmares and CVD in military veterans. METHODS: Participants were veterans (N = 3468; 77% male) serving since September 11, 2001, aged 38 years (SD = 10.4); approximately 30% were diagnosed with PTSD. Nightmare frequency and severity were assessed using the Davidson Trauma Scale (DTS). Self-reported medical issues were assessed using the National Vietnam Veterans Readjustment Study Self-report Medical Questionnaire. Mental health disorders were established using the Structured Clinical Interview for DSM-IV. The sample was stratified by the presence or absence of PTSD. Within-group associations between nightmare frequency and severity and self-reported CVD conditions, adjusting for age, sex, race, current smoking, depression, and sleep duration. RESULTS: Frequent and severe nightmares during the past week were endorsed by 32% and 35% of participants, respectively. Those endorsing nightmares that were frequent, severe, and the combination thereof were more likely to also evidence high blood pressure (ORs 1.42, OR 1.56, and OR 1.47, respectively) and heart problems (OR 1.43, OR 1.48, and OR 1.59, respectively) after adjusting for PTSD diagnosis and other covariates. CONCLUSIONS: Nightmare frequency and severity among veterans are associated with cardiovascular conditions, even after controlling for PTSD diagnosis. Study findings suggest that nightmares may be an independent risk factor for CVD. Additional research is needed to validate these findings using confirmed diagnoses and explore potential mechanisms.

Nightmare disorder and low back pain in veterans: cross-sectional association and effect over time.

Low back pain (LBP) disproportionately impacts US military veterans compared with nonveterans. Although the effect of psychological conditions on LBP is regularly studied, there is little published to date investigating nightmare disorder (NMD) and LBP. The purpose of this study was to (1) investigate whether an association exists between NMD and LBP and (2) estimate the effect of NMD diagnosis on time to LBP. We used a retrospective cohort design with oversampling of those with NMD from the Veterans Health Administration (n = 15 983). We used logistic regression to assess for a cross-sectional association between NMD and LBP and survival analysis to estimate the effect of NMD on time to LBP, up to 60-month follow-up, conditioning on age, sex, race, index year, Charlson Comorbidity Index, depression, anxiety, insomnia, combat exposure, and prisoner of war history to address confounding. Odds ratios (with 95% confidence intervals [CIs]) indicated a cross-sectional association of 1.35 (1.13 to 1.60) and 1.21 (1.02 to 1.42) for NMD and LBP within 6 months and 12 months pre- or post-NMD diagnosis, respectively. Hazard ratios (HRs) indicated the effect of NMD on time to LBP that was time-dependent-HR (with 95% CIs) 1.27 (1.02 to 1.59), 1.23 (1.03 to 1.48), 1.19 (1.01 to 1.40), and 1.10 (0.94 to 1.29) in the first 3, 6, 9, and 12 months post-diagnosis, respectively-approximating the null (1.00) at >12 months. The estimated effect of NMD on LBP suggests that improved screening for NMD among veterans may help clinicians and researchers predict (or intervene to reduce) risk of future back pain.

Biomarker clusters differentiate phenotypes of lumbar spine degeneration and low back pain: The Johnston County Osteoarthritis Project.

Objective: Describe the association between biomarkers and lumbar spine degeneration (vertebral osteophytes [OST], facet joint osteoarthritis [FOA], and disc space narrowing [DSN]), for persons with and without low back pain (LBP) and determine whether clusters based on biomarkers differentiate lumbar spine structure with and without LBP. Methods: Using data from the Johnston County Osteoarthritis Project (2006-2010), we measured serum N-cadherin, Keratin-19, Lumican, CXCL6, RANTES, HA, IL-6, BDNF, OPG, and NPY, and urinary CTX-II. Biomarkers were used to group participants using k-means cluster analysis. Logistic regression models were used to compare biomarker clusters. Results: The sample consisted of 731 participants with biospecimens and lumbar spine radiographic data. Three biomarker subgroups were identified: one characterized by structural degenerative changes; another characterized by structural degenerative changes and inflammation, with pain; and a referent cluster with lower levels of biomarkers, pain, and structural degenerative changes. Compared to the referent subgroup, the structural change subgroup was associated with DSN (OR = 1.94, 95% CI 1.30-2.90) and FOA (OR = 1.72, 95% CI 1.12-2.62), and the subgroup with structural degenerative change, inflammation, and pain was associated with OST with LBP (OR = 1.60, 95% CI 1.04-2.46), FOA with LBP (OR = 1.59, 95% CI 1.04-2.45), and LBP (OR = 1.63, 95% CI 1.11-2.41). The subgroup with structural degenerative changes was more likely to have OST (OR = 1.82, 95% CI 1.06-3.13) and less likely to have FOA with LBP (OR = 0.62, 95% CI 0.40-0.96) compared to the group with inflammation and pain. Conclusion: Clustering by biomarkers may assist in differentiating patients for specific clinical interventions aimed at decreasing LBP.

Untwisted α-Synuclein Filaments Formed in the Presence of Lipid Vesicles.

Accumulation of filamentous aggregates of α-synuclein is a pathological hallmark of several neurodegenerative diseases, including Parkinson's disease (PD). The interaction between α-synuclein and phospholipids has been shown to play a critical role in the aggregation of α-synuclein. Most structural studies have, however, been focused on α-synuclein filaments formed in the absence of lipids. Here, we report the structural investigation of α-synuclein filaments assembled under the quiescent condition in the presence of anionic lipid vesicles using electron microscopy (EM), including cryogenic electron microscopy (cryo-EM). Our transmission electron microscopy (TEM) analyses reveal that α-synuclein forms curly protofilaments at an early stage of aggregation. The flexible protofilaments were then converted to long filaments after a longer incubation of 30 days. More detailed structural analyses using cryo-EM reveal that the long filaments adopt untwisted structures with different diameters, which have not been observed in previous α-synuclein fibrils formed in vitro. The untwisted filaments are rather similar to straight filaments with no observable twist that are extracted from patients with dementia with Lewy bodies. Our structural studies highlight the conformational diversity of α-synuclein filaments, requiring additional structural investigation of not only more ex vivo α-synuclein filaments but also in vitro α-synuclein filaments formed in the presence of diverse cofactors to better understand the molecular basis of diverse molecular conformations of α-synuclein filaments.

Structure of the Flight Muscle Thick Filament from the Bumble Bee, Bombus ignitus, at 6 Å Resolution.

Four insect orders have flight muscles that are both asynchronous and indirect; they are asynchronous in that the wingbeat frequency is decoupled from the frequency of nervous stimulation and indirect in that the muscles attach to the thoracic exoskeleton instead of directly to the wing. Flight muscle thick filaments from two orders, Hemiptera and Diptera, have been imaged at a subnanometer resolution, both of which revealed a myosin tail arrangement referred to as "curved molecular crystalline layers". Here, we report a thick filament structure from the indirect flight muscles of a third insect order, Hymenoptera, the Asian bumble bee Bombus ignitus. The myosin tails are in general agreement with previous determinations from Lethocerus indicus and Drosophila melanogaster. The Skip 2 region has the same unusual structure as found in Lethocerus indicus thick filaments, an α-helix discontinuity is also seen at Skip 4, but the orientation of the Skip 1 region on the surface of the backbone is less angled with respect to the filament axis than in the other two species. The heads are disordered as in Drosophila, but we observe no non-myosin proteins on the backbone surface that might prohibit the ordering of myosin heads onto the thick filament backbone. There are strong structural similarities among the three species in their non-myosin proteins within the backbone that suggest how one previously unassigned density in Lethocerus might be assigned. Overall, the structure conforms to the previously observed pattern of high similarity in the myosin tail arrangement, but differences in the non-myosin proteins.

Tau induces formation of α-synuclein filaments with distinct molecular conformations.

Recent structural investigation of amyloid filaments extracted from human patients demonstrated that the ex vivo filaments associated with different disease phenotypes adopt diverse molecular conformations, which are different from those of in vitro amyloid filaments. A very recent cryo-EM structural study also revealed that ex vivo α-synuclein filaments extracted from multiple system atrophy patients adopt distinct molecular structures from those of in vitro α-synuclein filaments, suggesting the presence of co-factors for α-synuclein aggregation in vivo. Here, we report structural characterizations of α-synuclein filaments formed in the presence of a potential co-factor, tau, using cryo-EM and solid-state NMR. Our cryo-EM structure of the tau-promoted α-synuclein filaments reveals some similarities to one of the previously reported polymorphs of in vitro α-synuclein filaments in the core region, while illustrating distinct conformations in the N- and C-terminal regions. The structural study highlights the conformational plasticity of α-synuclein filaments and the importance of the co-factors, requiring additional structural investigation of not only more ex vivo α-synuclein filaments, but also in vitro α-synuclein filaments formed in the presence of diverse co-factors. The comparative structural analyses will help better understand molecular basis of diverse structures of α-synuclein filaments and possible relevance of each structure to the disease phenotype.

The myosin II coiled-coil domain atomic structure in its native environment.

The atomic structure of the complete myosin tail within thick filaments isolated from Lethocerus indicus flight muscle is described and compared to crystal structures of recombinant, human cardiac myosin tail segments. Overall, the agreement is good with three exceptions: the proximal S2, in which the filament has heads attached but the crystal structure doesn't, and skip regions 2 and 4. At the head-tail junction, the tail α-helices are asymmetrically structured encompassing well-defined unfolding of 12 residues for one myosin tail, ∼4 residues of the other, and different degrees of α-helix unwinding for both tail α-helices, thereby providing an atomic resolution description of coiled-coil "uncoiling" at the head-tail junction. Asymmetry is observed in the nonhelical C termini; one C-terminal segment is intercalated between ribbons of myosin tails, the other apparently terminating at Skip 4 of another myosin tail. Between skip residues, crystal and filament structures agree well. Skips 1 and 3 also agree well and show the expected α-helix unwinding and coiled-coil untwisting in response to skip residue insertion. Skips 2 and 4 are different. Skip 2 is accommodated in an unusual manner through an increase in α-helix radius and corresponding reduction in rise/residue. Skip 4 remains helical in one chain, with the other chain unfolded, apparently influenced by the acidic myosin C terminus. The atomic model may shed some light on thick filament mechanosensing and is a step in understanding the complex roles that thick filaments of all species undergo during muscle contraction.