Bone marrow lesion volume reduction is not associated with improvement of other periarticular bone measures: data from the Osteoarthritis Initiative

Introduction

We evaluated the associations between bone marrow lesion (BML) volume change and changes in periarticular bone mineral density (paBMD) as well as subchondral sclerosis to determine whether BML change is associated with other local bone changes.

Methods

The convenience sample comprised participants in the Osteoarthritis Initiative (OAI) with weight-bearing posterior-anterior knee radiographs and magnetic resonance images (MRIs) at the 24- and 48-month visits and dual-energy x-ray absorptiometry (DXA) at the 30-/36-month and 48-month visits. The right knee was assessed unless contraindicated for MRI. We used knee DXA scans to measure medial tibia paBMD and medial/lateral paBMD ratio (M:L paBMD). Knee radiographs were scored for sclerosis (grades 0 to 3) in the medial tibia. Two raters determined BML volume on sagittal fat-suppressed MRI by using a semiautomated segmentation method. To focus on knees with only medial tibia BML changes, knees with lateral tibial BMLs were excluded. Medial tibial BML volume change was classified into three groups: BML regression (lowest quartile of medial tibial BML volume change), no-to-minimal change (middle two quartiles), and BML progression (highest quartile). We used proportional odds logistic regression models to evaluate the association between quartiles of changes in medial paBMD or M:L paBMD ratio, as outcomes, and BML volume change.

Results

The sample (n = 308) included 163 (53%) female subjects, 212 (69%) knees with radiographic osteoarthritis, and participants with a mean age of 63.8 ± 9.3 years and mean body mass index of 29.8 ± 4.7 kg/m². We found an association between greater increases in medial tibia paBMD and BML regression (OR = 1.7 (95% confidence interval (CI) = 1.1 to 2.8)) and a similar trend for BML progression (OR = 1.6 (95% CI = 1.0 to 2.6]). We also detected associations between greater increase in M:L paBMD and BML regression (OR = 1.6 (95% CI = 1.0 to 2.7]) and BML progression (OR = 1.8 (95% CI = 1.1 to 3.0)), although BML regression had borderline statistical significance. The frequency of sclerosis progression in the medial tibia (n = 14) was greater among knees with BML progression or regression compared with knees without BML change (P = 0.01 and P = 0.04, respectively).

Conclusion

BML regression and BML progression are characterized by concurrent increases in paBMD and sclerosis, which are characteristic of increased radiographic osteoarthritis severity. At least during 24 months, BML regression is not representative of improvement in other periarticular bone measures.     

Profiling Protein Kinases and Other ATP Binding Proteins in Arabidopsis Using Acyl-ATP Probes

Many protein activities are driven by ATP binding and hydrolysis. Here, we explore the ATP binding proteome of the model plant Arabidopsis thaliana using acyl-ATP (AcATP)¹ probes. These probes target ATP binding sites and covalently label lysine residues in the ATP binding pocket. Gel-based profiling using biotinylated AcATP showed that labeling is dependent on pH and divalent ions and can be competed by nucleotides. The vast majority of these AcATP-labeled proteins are known ATP binding proteins. Our search for labeled peptides upon in-gel digest led to the discovery that the biotin moiety of the labeled peptides is oxidized. The in-gel analysis displayed kinase domains of two receptor-like kinases (RLKs) at a lower than expected molecular weight, indicating that these RLKs lost the extracellular domain, possibly as a result of receptor shedding. Analysis of modified peptides using a gel-free platform identified 242 different labeling sites for AcATP in the Arabidopsis proteome. Examination of each individual labeling site revealed a preference of labeling in ATP binding pockets for a broad diversity of ATP binding proteins. Of these, 24 labeled peptides were from a diverse range of protein kinases, including RLKs, mitogen-activated protein kinases, and calcium-dependent kinases. A significant portion of the labeling sites could not be assigned to known nucleotide binding sites. However, the fact that labeling could be competed with ATP indicates that these labeling sites might represent previously uncharacterized nucleotide binding sites. A plot of spectral counts against expression levels illustrates the high specificity of AcATP probes for protein kinases and known ATP binding proteins. This work introduces profiling of ATP binding activities of a large diversity of proteins in plant proteomes. The data have been deposited in ProteomeXchange with the identifier PXD000188.ATP binding and hydrolysis are the driving processes in all living organisms. Hundreds of cellular proteins are able to bind and hydrolyze ATP to unfold proteins, transport molecules over membranes, or phosphorylate small molecules or proteins. Proteins with very different structures are able to bind ATP. A large and important class of ATP binding proteins is that of the kinases, which transfer the gamma phosphate from ATP to substrates. Kinases, and particularly protein kinases, play pivotal roles in signaling and protein regulation.The genome of the model plant Arabidopsis thaliana encodes for over 1099 protein kinases and hundreds of other ATP binding proteins (1, 2). Protein kinases are involved in nearly all signaling cascades and regulate processes ranging from cell cycle to flowering and from immunity to germination. Many protein kinases in plants are receptor-like kinases (RLKs), often carrying extracellular leucine-rich repeats (LRRs). The RLK class contains at least 610 members (3), including famous examples such as receptors involved in development (e.g. BRI1, ER, CLV1) and immunity (e.g. FLS2, EFR). Other important classes are mitogen-activated protein (MAP) kinases (MPKs) (20 different members), MPK kinase kinase kinases (MAP3Ks) (60 different members (4)), and calcium-dependent protein kinases (CPKs) (34 different members (5)). Because of their diverse and important roles, protein kinases have been intensively studied in plant science. The current approach is to study protein kinases individually—a daunting task, considering the remaining hundreds of uncharacterized protein kinases. New approaches are necessary in order to study protein kinases and other ATP binding proteins globally rather than individually.ATP binding activities of protein kinases and other proteins can be detected globally by acyl-ATP (AcATP) probes (6, 7) (Fig. 1A). AcATP binds to the ATP pocket of ATP binding proteins and places the acyl group in close proximity to conserved lysine residues in the ATP binding pocket. The acyl phosphonate moiety serves as an electrophilic warhead that can be nucleophilically attacked by the amino group of the lysine, resulting in a covalent attachment of the acyl reporter of the AcATP probe on the lysine and a concomitant release of ATP. The reporter tag is usually a biotin to capture and identify the labeled proteins. Labeled proteins can be displayed on protein blots using streptavidin-HRP. However, because AcATP labels many ATP binding proteins and protein kinases are of relatively low abundance, mass spectrometry is more often used to identify and quantify labeling with AcATP probes. The analysis is preferably done using Xsite, a procedure that involves trypsination of the entire labeled proteome, followed by analysis of the biotinylated peptides rather than the biotinylated proteins (8). This “KiNativ ” approach provides enough depth and resolving power to monitor ∼160 protein kinases in a crude mammalian proteome (7). Of the 518 human protein kinases (9), 394 (76%) have been detected via AcATP labeling (6).Open in a separate windowFig. 1.Structure and mechanism of labeling with BHAcATP. A, BHAcATP contains ATP, an acyl phosphate reactive group, and a biotin tag. When BHAcATP binds to the ATP binding pocket of a protein, the amino group of the nearby lysine reacts with the carbonyl carbon, which results in the covalent binding of the biotin tag to the protein while ATP is released. B, typical BHAcATP labeling profile of Arabidopsis leaf proteome. Arabidopsis leaf extracts were labeled with BHAcATP and the biotinylated proteins were detected on protein blots using streptavidin-HRP. Coomassie Brilliant Blue staining indicates equal loading. Asterisks indicate endogenously biotinylated proteins MCCA and BCCP. White, black, and gray arrowheads indicate bands containing ATBP+RBCL, PGK1, and a mix of ATP binding proteins, respectively. Abbreviations: MCCA, 3-methylcrotonyl-CoA carboxylase; BCCP, biotin carboxyl carrier protein; ATPB, chloroplastic ATPase; RBCL, ribulose-bisphosphate carboxylase; PGK1, phosphoglycerate kinase-1.KiNativ has mostly been used to validate targets of human drugs that target protein kinases using competitive labeling experiments. This approach has been used to identify selective inhibitors of, for example, Parkinson''s disease protein kinase LRRK2 (10), the BMK1 and JNK MAP kinases (11, 12), and the mTOR kinase (13). Importantly, the correlation of the biological activity of protein-kinase-inhibiting drugs with inhibitor affinity detected using KiNativ is better than that achieved when affinities are determined by assays using heterologously expressed protein kinases (7). This improved correlation illustrates that assays in the native environment provide a more realistic measure of protein kinase function.In addition to characterizing inhibitors selectively, AcATP probes can also display differential ATP binding activities of protein kinases. For example, labeling with AcATP probes during infection with dengue virus displayed a 2- to 8-fold activation of a DNA-dependent protein kinase (14) Similarly, AcATP labeling revealed an unexpected Raf kinase activation in extracts upon protein kinase inhibitor treatment (7). In conclusion, profiling with AcATP probes is a powerful approach for monitoring protein kinases and offers unprecedented opportunities to identify selective protein kinase inhibitors and discover protein kinases with differential ATP binding activities.In this work, we introduce AcATP profiling of plant proteomes. In addition to the analysis of labeled peptides, we characterized labeling using gel-based approaches and discovered that biotin is often oxidized in this procedure. We also performed an in-depth analysis of labeling sites in proteins other than protein kinases, which had not been done before. We discuss labeling outside known nucleotide binding pockets and investigate the correlation of labeling sites with protein abundance. We describe 63 labeling sites of known nucleotide binding pockets, of which 24 represent a remarkable diversity of protein kinases, including several LRR-RLKs. This work launches a new approach to study ATP binding proteins in plant science.     

Electrical Vestibular Stimulation after Vestibular Deafferentation and in Vestibular Schwannoma

Background

Vestibular reflexes, evoked by human electrical (galvanic) vestibular stimulation (EVS), are utilized to assess vestibular function and investigate its pathways. Our study aimed to investigate the electrically-evoked vestibulo-ocular reflex (eVOR) output after bilateral and unilateral vestibular deafferentations to determine the characteristics for interpreting unilateral lesions such as vestibular schwannomas.

Methods

EVOR was recorded with dual-search coils as binocular three-dimensional eye movements evoked by bipolar 100 ms-step at EVS intensities of [0.9, 2.5, 5.0, 7.5, 10.0]mA and unipolar 100 ms-step at 5 mA EVS intensity. Five bilateral vestibular deafferented (BVD), 12 unilateral vestibular deafferented (UVD), four unilateral vestibular schwannoma (UVS) patients and 17 healthy subjects were tested with bipolar EVS, and five UVDs with unipolar EVS.

Results

After BVD, bipolar EVS elicited no eVOR. After UVD, bipolar EVS of one functioning ear elicited bidirectional, excitatory eVOR to cathodal EVS with 9 ms latency and inhibitory eVOR to anodal EVS, opposite in direction, at half the amplitude with 12 ms latency, exhibiting an excitatory-inhibitory asymmetry. The eVOR patterns from UVS were consistent with responses from UVD confirming the vestibular loss on the lesion side. Unexpectedly, unipolar EVS of the UVD ear, instead of absent response, evoked one-third the bipolar eVOR while unipolar EVS of the functioning ear evoked half the bipolar response.

Conclusions

The bidirectional eVOR evoked by bipolar EVS from UVD with an excitatory-inhibitory asymmetry and the 3 ms latency difference between normal and lesion side may be useful for detecting vestibular lesions such as UVS. We suggest that current spread could account for the small eVOR to 5 mA unipolar EVS of the UVD ear.     

Glucose-6-Phosphate Dehydrogenase Deficiency in Nigerian Children

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common human enzymopathy and in Sub-Saharan Africa, is a significant cause of infection- and drug-induced hemolysis and neonatal jaundice. Our goals were to determine the prevalence of G6PD deficiency among Nigerian children of different ethnic backgrounds and to identify predictors of G6PD deficiency by analyzing vital signs and hematocrit and by asking screening questions about symptoms of hemolysis. We studied 1,122 children (561 males and 561 females) aged 1 month to 15 years. The mean age was 7.4±3.2 years. Children of Yoruba ethnicity made up the largest group (77.5%) followed by those Igbo descent (10.6%) and those of Igede (10.2%) and Tiv (1.8%) ethnicity. G6PD status was determined using the fluorescent spot method. We found that the overall prevalence of G6PD deficiency was 15.3% (24.1% in males, 6.6% in females). Yoruba children had a higher prevalence (16.9%) than Igede (10.5%), Igbo (10.1%) and Tiv (5.0%) children. The odds of G6PD deficiency were 0.38 times as high in Igbo children compared to Yoruba children (p = 0.0500). The odds for Igede and Tiv children were not significantly different from Yoruba children (p = 0.7528 and 0.9789 respectively). Mean oxygen saturation, heart rate and hematocrit were not significantly different in G6PD deficient and G6PD sufficient children. The odds of being G6PD deficient were 2.1 times higher in children with scleral icterus than those without (p = 0.0351). In conclusion, we determined the prevalence of G6PD deficiency in Nigerian sub-populations. The odds of G6PD deficiency were decreased in Igbo children compared to Yoruba children. There was no association between vital parameters or hematocrit and G6PD deficiency. We found that a history of scleral icterus may increase the odds of G6PD deficiency, but we did not exclude other common causes of icterus such as sickle cell disease or malarial infection.     

Presynaptic to postsynaptic relationships of the neuromuscular junction are held constant across age and muscle fiber type

The neuromuscular junction (NMJ) displays considerable morphological plasticity as a result of differences in activity level, as well as aging. This is true of both presynaptic and postsynaptic components of the NMJ. Yet, despite these variations in NMJ structure, proper presynaptic to postsynaptic coupling must be maintained in order for effective cell‐to‐cell communication to occur. Here, we examined the NMJs of muscles with different activity profiles (soleus and EDL), on both slow‐ and fast‐twitch fibers in those muscles, and among young adult and aged animals. We used immunofluorescent techniques to stain nerve terminal branching, presynaptic vesicles, postsynaptic receptors, as well as fast/slow myosin heavy chain. Confocal microscopy was used to capture images of NMJs for later quantitative analysis. Data were subjected to a two‐way ANOVA (main effects for myofiber type and age), and in the event of a significant (p < 0.05) F ratio, a post hoc analysis was performed to identify pairwise differences. Results showed that the NMJs of different myofiber types routinely displayed differences in presynaptic and postsynaptic morphology (although the effect on NMJ size was reversed in the soleus and the EDL), but presynaptic to postsynaptic relationships were tightly maintained. Moreover, the ratio of presynaptic vesicles relative to nerve terminal branch length also was similar despite differences in muscles, their fiber type, and age. Thus, in the face of considerable overall structural differences of the NMJ, presynaptic to postsynaptic coupling remains constant, as does the relationship between presynaptic vesicles and the nerve terminal branches that support them. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 73: 744–753, 2013     

A Model of Chronic Nutrient Infusion in the Rat

Chronic exposure to excessive levels of nutrients is postulated to affect the function of several organs and tissues and to contribute to the development of the many complications associated with obesity and the metabolic syndrome, including type 2 diabetes. To study the mechanisms by which excessive levels of glucose and fatty acids affect the pancreatic beta-cell and the secretion of insulin, we have established a chronic nutrient infusion model in the rat. The procedure consists of catheterizing the right jugular vein and left carotid artery under general anesthesia; allowing a 7-day recuperation period; connecting the catheters to the pumps using a swivel and counterweight system that enables the animal to move freely in the cage; and infusing glucose and/or Intralipid (a soybean oil emulsion which generates a mixture of approximately 80% unsaturated/20% saturated fatty acids when infused with heparin) for 72 hr. This model offers several advantages, including the possibility to finely modulate the target levels of circulating glucose and fatty acids; the option to co-infuse pharmacological compounds; and the relatively short time frame as opposed to dietary models. It can be used to examine the mechanisms of nutrient-induced dysfunction in a variety of organs and to test the effectiveness of drugs in this context.     

Model-Based Assessment of Estuary Ecosystem Health Using the Latent Health Factor Index,with Application to the Richibucto Estuary

The ability to quantitatively assess ecological health is of great interest to those tasked with monitoring and conserving ecosystems. For decades, biomonitoring research and policies have relied on multimetric health indices of various forms. Although indices are numbers, many are constructed based on qualitative procedures, thus limiting the quantitative rigor of the practical interpretations of such indices. The statistical modeling approach to construct the latent health factor index (LHFI) was recently developed. With ecological data that otherwise are used to construct conventional multimetric indices, the LHFI framework expresses such data in a rigorous quantitative model, integrating qualitative features of ecosystem health and preconceived ecological relationships among such features. This hierarchical modeling approach allows unified statistical inference of health for observed sites (along with prediction of health for partially observed sites, if desired) and of the relevance of ecological drivers, all accompanied by formal uncertainty statements from a single, integrated analysis. Thus far, the LHFI approach has been demonstrated and validated in a freshwater context. We adapt this approach to modeling estuarine health, and illustrate it on the previously unassessed system in Richibucto in New Brunswick, Canada, where active oyster farming is a potential stressor through its effects on sediment properties. Field data correspond to health metrics that constitute the popular AZTI marine biotic index and the infaunal trophic index, as well as abiotic predictors preconceived to influence biota. Our paper is the first to construct a scientifically sensible model that rigorously identifies the collective explanatory capacity of salinity, distance downstream, channel depth, and silt–clay content–all regarded a priori as qualitatively important abiotic drivers–towards site health in the Richibucto ecosystem. This suggests the potential effectiveness of the LHFI approach for assessing not only freshwater systems but aquatic ecosystems in general.