Skeletal muscle expression of adipose-specific phospholipase in peripheral artery disease

Flow-limiting atherosclerotic lesions of arteries supplying the limbs are a cause of symptoms in patients with peripheral artery disease (PAD). Musculoskeletal metabolic factors also contribute to the pathophysiology of claudication, which is manifest as leg discomfort that impairs walking capacity. Accordingly, we conducted a case-control study to determine whether skeletal muscle metabolic gene expression is altered in PAD. Calf skeletal muscle gene expression of patients with PAD and healthy subjects was analyzed using microarrays. The top-ranking gene differentially expressed between PAD and controls (FDR < 0.001) was PLA2G16, which encodes adipose-specific phospholipase A2 (AdPLA) and is implicated in the maintenance of insulin sensitivity and regulation of lipid metabolism. Differential expression was confirmed by qRT-PCR; PLA2G16 was downregulated by 68% in patients with PAD (p < 0.001). Expression of Pla2g16 was then measured in control (db/+) and diabetic (db/db) mice that underwent unilateral femoral artery ligation. There was significantly reduced expression of Pla2g16 in the ischemic leg of both control and diabetic mice (by 51%), with significantly greater magnitude of reduction in the diabetic mice (by 79%). We conclude that AdPLA is downregulated in humans with PAD and in mice with hindlimb ischemia. Reduced AdPLA may contribute to impaired walking capacity in patients with PAD via its effects on skeletal muscle metabolism. Further studies are needed to fully characterize the role of AdPLA in PAD and to investigate its potential as a therapeutic target for alleviating symptoms of claudication.

Metabolic control of primed human pluripotent stem cell fate and function by the miR-200c-SIRT2 axis

A hallmark of cancer cells is the metabolic switch from oxidative phosphorylation (OXPHOS) to glycolysis, a phenomenon referred to as the 'Warburg effect', which is also observed in primed human pluripotent stem cells (hPSCs). Here, we report that downregulation of SIRT2 and upregulation of SIRT1 is a molecular signature of primed hPSCs and that SIRT2 critically regulates metabolic reprogramming during induced pluripotency by targeting glycolytic enzymes including aldolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and enolase. Remarkably, knockdown of SIRT2 in human fibroblasts resulted in significantly decreased OXPHOS and increased glycolysis. In addition, we found that miR-200c-5p specifically targets SIRT2, downregulating its expression. Furthermore, SIRT2 overexpression in hPSCs significantly affected energy metabolism, altering stem cell functions such as pluripotent differentiation properties. Taken together, our results identify the miR-200c-SIRT2 axis as a key regulator of metabolic reprogramming (Warburg-like effect), via regulation of glycolytic enzymes, during human induced pluripotency and pluripotent stem cell function.

Sun-induced fluorescence - a new probe of photosynthesis: First maps from the imaging spectrometer HyPlant

Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO2 uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun-induced fluorescence signal on the ground and on a coarse spatial scale using space-borne imaging spectrometers. Intermediate-scale observations using airborne-based imaging spectroscopy, which are critical to bridge the existing gap between small-scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun-induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun-induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun-induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun-induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.

Severe insulin resistance alters metabolism in mesenchymal progenitor cells

Donohue syndrome (DS) is characterized by severe insulin resistance due to mutations in the insulin receptor (INSR) gene. To identify molecular defects contributing to metabolic dysregulation in DS in the undifferentiated state, we generated mesenchymal progenitor cells (MPCs) from induced pluripotent stem cells derived from a 4-week-old female with DS and a healthy newborn male (control). INSR mRNA and protein were significantly reduced in DS MPC (for β-subunit, 64% and 89% reduction, respectively, P < .05), but IGF1R mRNA and protein did not differ vs control. Insulin-stimulated phosphorylation of INSR or the downstream substrates insulin receptor substrate 1 and protein kinase B did not differ, but ERK phosphorylation tended to be reduced in DS (32% decrease, P = .07). By contrast, IGF-1 and insulin-stimulated insulin-like growth factor 1 (IGF-1) receptor phosphorylation were increased in DS (IGF-1, 8.5- vs 4.5-fold increase; INS, 11- vs 6-fold; P < .05). DS MPC tended to have higher oxygen consumption in both the basal state (87% higher, P =.09) and in response to the uncoupler carbonyl cyanide-p-triflouromethoxyphenylhydrazone (2-fold increase, P =.06). Although mitochondrial DNA or mass did not differ, oxidative phosphorylation protein complexes III and V were increased in DS (by 37% and 6%, respectively; P < .05). Extracellular acidification also tended to increase in DS (91% increase, P = .07), with parallel significant increases in lactate secretion (34% higher at 4 h, P < .05). In summary, DS MPC maintain signaling downstream of the INSR, suggesting that IGF-1R signaling may partly compensate for INSR mutations. However, alterations in receptor expression and pathway-specific defects in insulin signaling, even in undifferentiated cells, can alter cellular oxidative metabolism, potentially via transcriptional mechanisms.

Metabolic modeling of muscle metabolism identifies key reactions linked to insulin resistance phenotypes

Objective

Dysregulated muscle metabolism is a cardinal feature of human insulin resistance (IR) and associated diseases, including type 2 diabetes (T2D). However, specific reactions contributing to abnormal energetics and metabolic inflexibility in IR are unknown.

Methods

We utilize flux balance computational modeling to develop the first systems-level analysis of IR metabolism in fasted and fed states, and varying nutrient conditions. We systematically perturb the metabolic network to identify reactions that reproduce key features of IR-linked metabolism.

Results

While reduced glucose uptake is a major hallmark of IR, model-based reductions in either extracellular glucose availability or uptake do not alter metabolic flexibility, and thus are not sufficient to fully recapitulate IR-linked metabolism. Moreover, experimentally-reduced flux through single reactions does not reproduce key features of IR-linked metabolism. However, dual knockdowns of pyruvate dehydrogenase (PDH), in combination with reduced lipid uptake or lipid/amino acid oxidation (ETFDH), does reduce ATP synthesis, TCA cycle flux, and metabolic flexibility. Experimental validation demonstrates robust impact of dual knockdowns in PDH/ETFDH on cellular energetics and TCA cycle flux in cultured myocytes. Parallel analysis of transcriptomic and metabolomics data in humans with IR and T2D demonstrates downregulation of PDH subunits and upregulation of its inhibitory kinase PDK4, both of which would be predicted to decrease PDH flux, concordant with the model.

Conclusions

Our results indicate that complex interactions between multiple biochemical reactions contribute to metabolic perturbations observed in human IR, and that the PDH complex plays a key role in these metabolic phenotypes.

Topology and self-assembly of defect-colloidal superstructure in confined chiral nematic liquid crystals

We describe formation of defect-colloidal superstructures induced by microspheres with normal surface anchoring dispersed in chiral nematic liquid crystals in confinement-unwound homeotropic cells. Using three-dimensional nonlinear optical imaging of the director field, we demonstrate that some of the induced defects have nonsingular solitonic nature while others are singular point and line topological defects. The common director structures induced by individual microspheres have dipolar symmetry. These topological dipoles are formed by the particle and a hyperbolic point defect (or small disclination loop) of elementary hedgehog charge opposite to that of a sphere with perpendicular boundary conditions, which in cells with thickness over equilibrium cholesteric pitch ratio approaching unity are additionally interspaced by a looped double-twist cylinder of continuous director deformations. The long-range elastic interactions are probed by holographic optical tweezers and videomicroscopy, providing insights to the physical underpinnings behind self-assembled colloidal structures entangled by twisted solitons. Computer-simulated field and defect configurations induced by the colloidal particles and their assemblies, which are obtained by numerically minimizing the Landau-de Gennes free energy, are in agreement with the experimental findings.

Self-assembly of skyrmion-dressed chiral nematic colloids with tangential anchoring

We describe dipolar nematic colloids comprising mutually bound solid microspheres, three-dimensional skyrmions, and point defects in a molecular alignment field of chiral nematic liquid crystals. Nonlinear optical imaging and numerical modeling based on minimization of Landau-de Gennes free energy reveal that the particle-induced skyrmions resemble torons and hopfions, while matching surface boundary conditions at the interfaces of liquid crystal and colloidal spheres. Laser tweezers and videomicroscopy reveal that the skyrmion-colloidal hybrids exhibit purely repulsive elastic pair interactions in the case of parallel dipoles and an unexpected reversal of interaction forces from repulsive to attractive as the center-to-center distance decreases for antiparallel dipoles. The ensuing elastic self-assembly gives rise to colloidal chains of antiparallel dipoles with particles entangled by skyrmions.

Assessment of pollen reward and pollen availability in Solanum stramoniifolium and Solanum paniculatum for buzz-pollinating carpenter bees

The two widespread tropical Solanum species S. paniculatum and S. stramoniifolium are highly dependent on the visits of large bees that pollinate the flowers while buzzing them. Both Solanum species do not offer nectar reward; the rewarding of bees is thus solely dependent on the availability of pollen. Flower visitors are unable to visually assess the amount of pollen, because the pollen is hidden in poricidal anthers. In this study we ask whether and how the amount of pollen determines the attractiveness of flowers for bees. The number of pollen grains in anthers of S. stramoniifolium was seven times higher than in S. paniculatum. By contrast, the handling time per five flowers for carpenter bees visiting S. paniculatum was 3.5 times shorter than of those visiting S. stramoniifolium. As a result foraging carpenter bees collected a similar number of pollen grains per unit time on flowers of both species. Experimental manipulation of pollen availability by gluing the anther pores showed that the carpenter bees were unable to detect the availability of pollen by means of chemical cues before landing and without buzzing. Our study shows that the efficiency of pollen collecting on S. paniculatum is based on large inflorescences with short between-flower search times and short handling time of individual flowers, whereas that of S. stramoniifolium relies on a large amount of pollen per flower. Interestingly, large carpenter bees are able to adjust their foraging behaviour to drastically different strategies of pollen reward in otherwise very similar plant species.

Adenylate kinase 2 links mitochondrial energy metabolism to the induction of the unfolded protein response

The unfolded protein response (UPR) is a homeostatic signaling mechanism that balances the protein folding capacity of the endoplasmic reticulum (ER) with the secretory protein load of the cell. ER protein folding capacity is dependent on the abundance of chaperones, which is increased in response to UPR signaling, and on a sufficient ATP supply for their activity. An essential branch of the UPR entails the splicing of XBP1 mRNA to form the XBP1 transcription factor. XBP1 has been shown to be required during adipocyte differentiation, enabling mature adipocytes to secrete adiponectin, and during differentiation of B cells into antibody-secreting plasma cells. Here we find that adenylate kinase 2 (AK2), a mitochondrial enzyme that regulates adenine nucleotide interconversion within the intermembrane space, is markedly induced during adipocyte and B cell differentiation. Depletion of AK2 by RNAi impairs adiponectin secretion in 3T3-L1 adipocytes, IgM secretion in BCL1 cells, and the induction of the UPR during differentiation of both cell types. These results reveal a new mechanism by which mitochondria support ER function and suggest that specific mitochondrial defects may give rise to impaired UPR signaling. The requirement for AK2 for UPR induction may explain the pathogenesis of the profound hematopoietic defects of reticular dysgenesis, a disease associated with mutations of the AK2 gene in humans.

Enhanced angiogenesis in obesity and in response to PPARgamma activators through adipocyte VEGF and ANGPTL4 production

PPARgamma activators such as rosiglitazone (RSG) stimulate adipocyte differentiation and increase subcutaneous adipose tissue mass. However, in addition to preadipocyte differentiation, adipose tissue expansion requires neovascularization to support increased adipocyte numbers. Paradoxically, endothelial cell growth and differentiation is potently inhibited by RSG in vitro, raising the question of how this drug can induce an increase in adipose tissue mass while inhibiting angiogenesis. We find that adipose tissue from mice treated with RSG have increased capillary density. To determine whether adipose tissue angiogenesis was stimulated by RSG, we developed a novel assay to study angiogenic sprout formation ex vivo. Angiogenic sprout formation from equally sized adipose tissue fragments, but not from aorta rings, was greatly increased by obesity and by TZD treatment in vivo. To define the mechanism involved in RSG-stimulated angiogenesis in adipose tissue, the expression of proangiogenic factors by adipocytes was examined. Expression of VEGFA and VEGFB, as well as of the angiopoietin-like factor-4 (ANGPTL4), was stimulated by in vivo treatment with RSG. To define the potential role of these factors, we analyzed their effects on endothelial cell growth and differentiation in vitro. We found that ANGPTL4 stimulates endothelial cell growth and tubule formation, albeit more weakly than VEGF. However, ANGPTL4 mitigates the growth inhibitory actions of RSG on endothelial cells in the presence or absence of VEGF. Thus, the interplay between VEGF and ANGPTL4 could lead to a net expansion of the adipose tissue capillary network, required for adipose tissue growth, in response to PPARgamma activators.

Paradoxical effect of mitochondrial respiratory chain impairment on insulin signaling and glucose transport in adipose cells

Adipocyte function is crucial for the control of whole body energy homeostasis. Pathway analysis of differentiating 3T3-L1 adipocytes reveals that major metabolic pathways induced during differentiation involve mitochondrial function. However, it is not clear why differentiated white adipocytes require enhanced respiratory chain activity relative to pre-adipocytes. To address this question, we used small interference RNA to interfere with the induction of the transcription factor Tfam, which is highly induced between days 2 and 4 of differentiation and is crucial for replication of mitochondrial DNA. Interference with Tfam resulted in cells with decreased respiratory chain capacity, reflected by decreased basal oxygen consumption, and decreased mitochondrial ATP synthesis, but no difference in many other adipocyte functions or expression levels of adipose-specific genes. However, insulin-stimulated GLUT4 translocation to the cell surface and subsequent glucose transport are impaired in Tfam knockdown cells. Paradoxically, insulin-stimulated Akt phosphorylation is significantly enhanced in these cells. These studies reveal independent links between mitochondrial function, insulin signaling, and glucose transport, in which impaired respiratory chain activity enhances insulin signaling to Akt phosphorylation, but impairs GLUT4 translocation. These results indicate that mitochondrial respiratory chain dysfunction in adipocytes can cause impaired insulin responsiveness of GLUT4 translocation by a mechanism downstream of the Akt protein kinase.

Cidea is associated with lipid droplets and insulin sensitivity in humans

Storage of energy as triglyceride in large adipose-specific lipid droplets is a fundamental need in all mammals. Efficient sequestration of fat in adipocytes also prevents fatty acid overload in skeletal muscle and liver, which can impair insulin signaling. Here we report that the Cide domain-containing protein Cidea, previously thought to be a mitochondrial protein, colocalizes around lipid droplets with perilipin, a regulator of lipolysis. Cidea-GFP greatly enhances lipid droplet size when ectopically expressed in preadipocytes or COS cells. These results explain previous findings showing that depletion of Cidea with RNAi markedly elevates lipolysis in human adipocytes. Like perilipin, Cidea and the related lipid droplet protein Cidec/FSP27 are controlled by peroxisome proliferator-activated receptor gamma (PPARgamma). Treatment of lean or obese mice with the PPARgamma agonist rosiglitazone markedly up-regulates Cidea expression in white adipose tissue (WAT), increasing lipid deposition. Strikingly, in both omental and s.c. WAT from BMI-matched obese humans, expression of Cidea, Cidec/FSP27, and perilipin correlates positively with insulin sensitivity (HOMA-IR index). Thus, Cidea and other lipid droplet proteins define a novel, highly regulated pathway of triglyceride deposition in human WAT. The data support a model whereby failure of this pathway results in ectopic lipid accumulation, insulin resistance, and its associated comorbidities in humans.

Keystone meeting summary: 'Adipogenesis, obesity, and inflammation' and 'Diabetes mellitus and the control of cellular energy metabolism, ' January 21-26, 2006, Vancouver, Canada

The dysregulation of specific cellular functions in adipocytes, muscle cells, beta cells, and the liver leads to changes in systemic metabolic processes and ultimately to the pathophysiological manifestations that cause type 2 diabetes. The underlying cellular mechanisms are complex. The two meetings summarized here aimed to highlight the recent advances in our understanding of the molecular basis of feeding and nutrient storage and on the molecular consequences of obesity in terms of promoting risk for type 2 diabetes and cardiovascular disease.

[The arthroscopic SLAP refixation]

Lesions of the superior glenoid labrum and the insertion of the biceps tendon are a common cause for shoulder pain in patients performing overhead sports. The therapeutic management depends on the type of lesion, and should be carried out using an arthroscopic procedure. While type I SLAP lesions should be treated conservatively or with simple debridement, SLAP II, IV, and V lesions, with a detachment of the labrumanchor- complex, should be refixed with suture anchors. Only in cases of type III lesions with a bucket handle-like lesion of the labrum, but stable insertion of the biceps tendon, a simple debridement can be performed. From the biomechanical point of view, large type III lesions should also be reconstructed. To improve the arthroscopic view for preparation of the glenoid neck, an intraarticular loop ("Imhoff-suspension sling") can prevent the posterosuperior labrum from falling into the joint. The arthroscopic SLAP refixation is a technically highly demanding procedure which provides good clinical results for the patient.

[Biomechanical tests for type II SLAP lesions of the shoulder joint before and after arthroscopic repair]

Superior labral anterior-to-posterior (SLAP) lesions can cause shoulder pain partly by causing glenohumeral instability. The purpose of this study was to examine the effect of a simulated type II SLAP lesion and subsequent repair on glenohumeral translation of the vented shoulder. In eight cadaver joints, a robotic/UFS testing system was used to measure joint translation by applying an anterior, posterior, or inferior load of 50 N to each shoulder. The "apprehension tests" for anterior and posterior instability were simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm or a posterior load of 50 N with an internal rotation torque of 3 Nm. Each loading condition was applied at 30 degrees and 60 degrees of glenohumeral abduction with a constant joint compressive load (44 N) to the intact, simulated SLAP lesion, and repaired shoulder. Repair of the type II SLAP was then performed by placing a Suretac through the labrum both anterior and posterior to the biceps anchor and testing was repeated. ANOVA was used to compare translation of the intact joint, the joint after the type II SLAP lesion had been simulated, and after repair. At 30 degrees of abduction, anterior translation of the intact vented shoulder joint from anterior loading was 18.7+/-8.5 mm and increased to 26.2+/-6.5 mm after simulation of the type II SLAP lesion ( p< or =0.05). The arthroscopic repair did not restore anterior translation (23.9+/-8.6 mm) to the same degree as the intact joint ( p> or =0.05). At 60 degrees of abduction, anterior translation of 16.6+/-9.6mm in the intact joint was not significantly increased at 19.4+/-10.1 after simulation of the type II SLAP lesion ( p=0.0527). AP loading also resulted in inferior translation. At 30 degrees of abduction it was 3.8+/-4.0 mm in the intact joint and increased to 8.5+/-5.4 mm after the type II SLAP lesion ( p< or =0.05. After repair the inferior translation decreased significantly to 6.7+/-5.3 mm ( p< or =0.05). Although inferior translations were less at 60 degrees of abduction, results were similar to those at 30 degrees after repair. There were no significant increases in translation after SI/AP combined external rotation torque or posterior-anterior combined internal rotation torque loading. In this study the repair of a type II SLAP lesion only partially restored translations to the same degree as an intact vented shoulder joint. Therefore, improved repair techniques or an anteroinferior capsulolabral procedure in addition to the type II SLAP lesion repair might be needed to restore normal joint function.

[Normal anatomical variants of the superior labrum biceps tendon anchor complex. Anatomical and magnetic resonance findings]

There are difficulties in diagnosing pathologies of the labrum-biceps tendon complex (LBTC) because of the great individual variability of this structure. Anatomical variations, such as the sublabral recess, are frequently found and can also be misinterpreted as Andrews or SLAP II lesions. The etiology and mechanisms of creating such a sublabral recess are not exactly known. The examination of 31 cadaveric shoulder specimens from an age group between 49.3 and 83.6 years showed a sublabral recess in 63.6-85%. This high frequency of sublabral detachment of the labrum in older patients indicates that according to the high range of motion of the humeral head and therefore the changing angle of the long biceps tendon (LBS) a certain mobility of the superior LBTC is physiological and should not necessarily be seen as a sign of instability. Besides mobility-increasing factors such as overhead professions and sports with high repetitive maximal abduction and external rotation and the individual age, the type of insertion of the LBT at the glenoid influences the development of sublabral recess. Accordingly, posterior oriented insertion types of the LBT determine deeper and more posterior oriented sublabral recesses whereas in cases of anterior directed types of insertions no or less deep recesses can be found. Anamnestic aspects, such as the mechanism of injury and overhead activities, these macroscopic and functional associations in MR arthrography and arthroscopic inspection have to be considered in order to differentiate between physiological and traumatic changes of the labrum-biceps tendon complex.

[Biomechanical investigations for the development of a SLAP-II-lesion]

The superior labral-biceps-tendon-complex forms an anatomical and functional unit and combines static and dynamic elements of shoulder stability. At present, only theoretical hypotheses exist on the etiology of the microtraumatic SLAP-II-lesion. To gain further insight into this, an instrument was developed to simulate throwing motions such as the late-cocking/early acceleration phase as well as deceleration/follow-through. Sixteen freshly frozen shoulder specimens were tested, varying the loads on the biceps tendon (25 N, 50 N, 100 N) and the compression of the humeral head against the glenoid (25 N, 50 N, 80 N). Each shoulder had to run through a certain number of cycles during the particular phase of throwing. The tests were stopped after a SLAP-II-lesion was observed, or after a limit of 15,000 cycles. Every 1,000 cycles the results of the tests were checked arthroscopically. A SLAP-II-lesion developed in only 10% of the specimens during the acceleration/ late cocking phase whereas in the deceleration/ follow-through phase 83% developed such a lesion. According to our results, the deceleration/follow-through of the throwing motion seems to be responsible for creating microtraumatic SLAP-II-lesions. One reason is the loss of the centering function of the long head of the biceps tendon during total internal rotation, another is the increased posterosuperior translation of the humeral head in this position, which leads to a non-physiological contact, creating lesions in this area due to the large sheering forces.

[SLAP lesions as a cause of posterior instability]

SLAP lesions disrupt the perilabral architecture, but so far there have been no reports about posterior instability due to SLAP lesions. In a prospective study of 30 patients with recurrent posterior instability, we found SLAP lesions as a reason for instability in three cases. The purpose of this study is to point out that SLAP lesions can be a cause of posterior instability. Thirty patients with clinical posterior shoulder instability underwent diagnostic arthroscopy before operative stabilization procedures, three of whom (three males, aged 29-51 years) showed a SLAP lesion (once case each of types II, III, and IV) as a cause of posterior instability. All three patients had a history of a fall on the outstretched arm. All patients underwent arthroscopic refixation of the labrum. After arthroscopic refixation of the SLAP lesions, two patients were completely stable (SLAP II and III), whereas one patient (SLAP IV) reported microinstability during overhead activity but complete stability during activity of daily living. The same patient complained about moderate pain in extreme external-flexion rotation with slightly reduced range of motion in external-flexion position. All other patients were free of pain and showed free range of motion. Our results demonstrate that SLAP lesions can be a cause for posterior shoulder instability. In our cases, posterior shoulder instability caused by SLAP lesions was successfully treated by arthroscopic refixation of the torn biceps anchor. When treating posterior shoulder instability, SLAP lesions should be taken into account.

Regulation of the SHP-2 tyrosine phosphatase by a novel cholesterol- and cell confluence-dependent mechanism

Endothelial cells approaching confluence exhibit marked decreases in tyrosine phosphorylation of receptor tyrosine kinases and adherens junctions proteins, required for cell cycle arrest and adherens junctions stability. Recently, we demonstrated a close correlation in endothelial cells between membrane cholesterol and tyrosine phosphorylation of adherens junctions proteins. Here, we probe the mechanistic basis for this correlation. We find that as endothelial cells reach confluence, the tyrosine phosphatase SHP-2 is recruited to a low-density membrane fraction in a cholesterol-dependent manner. Binding of SHP-2 to this fraction was not abolished by phenyl phosphate, strongly suggesting that this binding was mediated by other regions of SHP-2 beside its SH2 domains. Annexin II, previously implicated in cholesterol trafficking, was associated in a complex with SHP-2, and both proteins localized to adhesion bands in confluent endothelial monolayers. These studies reveal a novel, cholesterol-dependent mechanism for the recruitment of signaling proteins to specific plasma membrane domains via their interactions with annexin II.

Expression of two membrane fusion proteins, synaptosome-associated protein of 25 kDa and vesicle-associated membrane protein, in choroid plexus epithelium

In addition to being the major site of cerebrospinal fluid formation, the choroid plexus epithelium emerges as an important source of polypeptides in the brain. Physiologically regulated release of some polypeptides synthesized by the choroid plexus has been shown. The molecular mechanisms underlying this polypeptide secretion have not been characterized, however. In the present study, synaptosome-associated protein of 25 kDa and vesicle-associated membrane protein, two membrane fusion proteins playing a critical role in exocytosis in neurons and endocrine cells, were found to be expressed in the choroid plexus epithelium. It was also shown that in choroidal epithelium, synaptosome-associated protein of 25 kDa and vesicle-associated membrane protein stably interact. Two members of the vesicle-associated membrane protein family, vesicle-associated membrane protein-1 and vesicle-associated membrane protein-2, were expressed in the rat choroid plexus at the messenger RNA and protein level. However, their newly discovered isoforms, vesicle-associated membrane protein-1b and vesicle-associated membrane protein-2b, produced by alternative RNA splicing, were not detected in choroidal tissue. Immunohistochemistry demonstrated that vesicle-associated membrane protein is confined to the cytoplasm of choroidal epithelium, whereas synaptosome-associated protein of 25 kDa is associated with plasma membranes, albeit with a varied cellular distribution among species studied. Specifically, in the rat choroid plexus, synaptosome-associated protein of 25 kDa was localized to the basolateral membrane domain of choroidal epithelium and was expressed in small groups of cells. In comparison, in ovine and human choroidal tissues, apical staining for synaptosome-associated protein of 25 kDa was found in the majority of epithelial cells. These species-related differences in cellular synaptosome-associated protein of 25 kDa distribution suggested that the synaptosome-associated protein of 25 kDa homologue, synaptosome-associated protein of 23 kDa, is also expressed in the rat choroid plexus, which was confirmed by reverse-transcriptase polymerase chain reaction. Our findings suggest that synaptosome-associated protein of 25 kDa and vesicle-associated membrane protein are involved in secretion of polypeptides from the choroid plexus epithelium. The presence of synaptosome-associated protein of 25 kDa and its homologue as well as multiple isoforms of vesicle-associated membrane protein in choroidal epithelium may play a role in the apical versus basolateral targeting of secretory vesicles.

[Development of a 3-dimensional method to determine the tibial slope with multislice-CT]

AIM

The measurement or, respectively, the correction of the tibial slope is an important subject in the field of knee arthroplasty and in the procedure of cruciate ligament reconstruction. However, a valid value of the tibial slope cannot be obtained from the conventional plain X-rays in a reproducible way. The aim of this study was to evaluate the proximal tibial slope with a new CT measurement system and to compare the values with the X-ray method.

METHOD

Using 6 cadaver tibiae, the antero-posterior slope of the proximal tibia was measured at 0 degrees, 2.5 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees, 30 degrees internal rotation using the plain X-ray and spiral CT (3D-MPR reconstruction). Both methods were compared.

RESULTS

The variation of the measurement of the tibial slope with the X-ray method was > 5 degrees even if the optimal 0 degrees rotation in the lateral view was applied. Moreover, the measurement error increased to 14 degrees while increasing the rotation of the tibia. Using the new CT system, the error was less than 3 degrees in all measurements.

CONCLUSION

The measurement of the tibial slope in the conventional X-ray technique showed a high variation of the values depending on the rotation of the tibia in the lateral view. In contrast, the measurements with the new CT system represented a precise method with a small variation of the tibial slope values. For this reason detailed questions regarding the precise anatomy of the proximal tibia cannot be answered precisely with plain X-rays.

Mitochondrial biogenesis and remodeling during adipogenesis and in response to the insulin sensitizer rosiglitazone

White adipose tissue is an important endocrine organ involved in the control of whole-body metabolism, insulin sensitivity, and food intake. To better understand these functions, 3T3-L1 cell differentiation was studied by using combined proteomic and genomic strategies. The proteomics approach developed here exploits velocity gradient centrifugation as an alternative to isoelectric focusing for protein separation in the first dimension. A 20- to 30-fold increase in the concentration of numerous mitochondrial proteins was observed during adipogenesis, as determined by mass spectrometry and database correlation analysis. Light and electron microscopy confirmed a large increase in the number of mitochondrion profiles with differentiation. Furthermore, mRNA profiles obtained by using Affymetrix GeneChips revealed statistically significant increases in the expression of many nucleus-encoded mitochondrial genes during adipogenesis. Qualitative changes in mitochondrial composition also occur during adipose differentiation, as exemplified by increases in expression of proteins involved in fatty acid metabolism and of mitochondrial chaperones. Furthermore, the insulin sensitizer rosiglitazone caused striking changes in mitochondrial shape and expression of selective mitochondrial proteins. Thus, although mitochondrial biogenesis has classically been associated with brown adipocyte differentiation and thermogenesis, our results reveal that mitochondrial biogenesis and remodeling are inherent to adipose differentiation per se and are influenced by the actions of insulin sensitizers.

[Mega-OATS. Technique and outcome]

Big osteochondral defects in the weight-bearing zone of the medial respectively the lateral femoral condyle are still an unsolved problem especially in younger patients. The transfer of the posterior aspect of the femoral condyle was described as a salvage procedure. Mega-OATS is a technical improvement of the transfer of the posterior condyle-procedure. Essential advantages of the conventional OATS-technique are integrated in the Mega-OATS procedure, so that iatrogenic lesions of the transferred cartilage by press-fit-fixation and secondary hardware removal can be avoided. However, the Mega-OATS procedure itself remains a salvage procedure and should only be reserved for younger patients. The results of the first series of 17 patients (average follow-up 12 (5-19) months) showed an improvement of quality of life and a significant (p = 0.003) increase in the Lysholm-score.

Precision of ACL tunnel placement using traditional and robotic techniques

The objective of this study was to examine the precision of ACL tunnel placement using: (1) CASPAR (orto MAQUET GmbH Co. KG)--an active robotic system, and (2) four orthopedic surgeons with various levels of experience (between 100 and 3,500 ACL reconstructions). The robotic system and each surgeon drilled tunnels for ACL reconstruction in 10 plastic knees (total n = 50) that included a reference cube in the medial aspect of the proximal tibia and distal femur. For the robotic system, the placement of each tunnel was planned preoperatively using custom software and CT data for each femur and tibia. The robotic system then drilled the tunnels in the femur and tibia based on the preoperative plan. For the surgeons, tunnel placement was accomplished using their preferred technique, which was based on the one-incision arthroscopic technique. The distribution of intra-articular points on the tibia was contained within a sphere of radius 2.0 mm (robot system), 2.1 mm (Fellow 1), 2.4 mm (Fellow 2), 3.4 mm (Experienced Surgeon 1), or 2.0 mm (Experienced Surgeon 2). On the femur, no significant differences in the distribution of intra-articular points could be demonstrated between the robotic system (2.1 mm), Fellow 1 (4.5 mm), Fellow 2 (4.1 mm), Experienced Surgeon 1 (2.3 mm), and Experienced Surgeon 2 (3.0 mm). The direction of the tunnels drilled in the femur and tibia was different with the robotic and traditional techniques. However, the robotic system had the most consistent tunnel directions, while the surgeons' tunnels were more dispersed. Variation in surgeon precision of tunnel placement for ACL reconstruction is greater on the femur than the tibia, and this can be correlated with experience. Our data also suggest that the robotic system has the same precision as the most experienced surgeons.

[Axis deviation, cartilage damage and cruciate ligament rupture--concomitant interventions in replacement of the anterior cruciate ligament]

BACKGROUND

Osteochondral lesions and osteoarthritis in young patients are often caused by chronic knee instability and varus malalignment. We present the indications, operative technique, and results for the combined operation of high tibial osteotomy and cruciate ligament reconstruction.

MATERIALS AND METHODS

From April 1996 until December 2000, 58 patients (average age: 33 years) underwent simultaneous osteotomy (57 correcting valgus, 1 valgus malalignment) and cruciate ligament reconstruction (49 ACL, 7 PCL, 2 ACL & PCL) which was routinely performed with an arthroscopic technique after completion of the osteotomy (closed wedge technique). Average correction angle of the osteotomy was 7 degrees (4-10 degrees) with a mean malalignment of 5 degrees (0-10 degrees). Thirteen patients underwent additional cartilage surgery (osteochondral autograft transplantation, autologous chondrocyte transplantation, microfracturing), and two patients were implanted with a collagen meniscus (CMI) at the same time.

RESULTS

Preoperatively the Lysholm score was 66 (35-81) points and increased to 81 (74-95), 87 (79-99), and 93 (88-99) points 3, 6, and 12 months after surgery, respectively. Subjectively all patients reported an improvement of preoperative swelling, pain, and instability. Additional cartilage surgery or meniscus implantation did not significantly alter the clinical score values. Complications were noted in four patients.

CONCLUSIONS

Unstable knees with varus malalignment can be sufficiently treated by osteotomy and cruciate ligament reconstruction at the same time, suggesting that unicompartimental decompression and treatment of instability is a causal and cost-effective therapy delaying the progression of osteoarthritis and minimizing clinical symptoms. Performing both operations in one procedure facilitates early rehabilitation and the return of these patients to the activities of daily living and sports.

[Diagnostic imaging after autologous chondrocyte transplantation. Correlation of magnetic resonance tomography, histological and arthroscopic findings]

Autologous chondrocyte transplantation (ACT) is a newly therapy option for treatment of cartilage damage. Since 1996 we performed the ACT in 10 patients with 14 cartilage damages. Magnetic resonance imaging (MRI) is a non-invasive method for postoperative controlling the transplantation area. The MRI showed in the first 3-6 months postoperatively signal irregularities with partial gadolinium uptake at the transplantation site. Arthroscopically the transplantation site was spongy, when it was probed and at the histological examination there was a hyalinlike appearance of the cells. 1 year postoperatively it seemed that process of reparation was finished. There was no more Gadolinium-uptake at the transplantation site and the borders of the transplant were hardly visible. The histological examination revealed hyalinlike repair tissue with a more columnar appearance of the cells. The Lysholm Score improved from 78 to 92 points, 1 year postoperatively.

Foreign-body reaction to the bioabsorbable suretac device

SUMMARY

Arthroscopic shoulder stabilization with the bioabsorbable Suretac device (Acufex Microsurgical, Mansfield, MA) offers some technical advantages compared with other approaches. However, in 4 patients (3 men, 1 woman; between 20 and 35 years of age) with 3 SLAP lesions grades 2 and 1 post-traumatic anterior shoulder instability, breakage and early loosening of the Suretac device was observed. All patients complained about shoulder pain and loss of active and passive motion. The arthroscopic examination revealed a massive synovitis without positive cultures. Loose fragments of the Suretac device spread in the joint cavity and induced a foreign-body reaction. Histologically, there was a massive infiltration of phagocytic cells (histiocytes, multinucleated giant cells) and birefringent polymeric particles surrounded by or within histiocytes and multinucleated giant cells. All patients underwent arthroscopic synovectomy. Because of instability, 2 of them required restabilization, which was performed with suture anchors (Fastak [Arthrex, Naples, FL], Mitek [Mitek Division, Ethicon, Norderstedt, Germany]). Postoperatively all patients were pain free, progressing to full active and passive range of motion. Our patients suffered from a mechanical failure rather than from a predisposition to exaggerated inflammatory response. According to this observation, the Suretac device seems to be prone to early failure in patients with SLAP lesions because of its biodegradability.

Treatment of experimental staphylococcal endocarditis due to a strain with reduced susceptibility in vitro to vancomycin: efficacy of ampicillin-sulbactam

We evaluated several 3-day antimicrobial regimens in the treatment of experimental endocarditis caused by an oxacillin-resistant Staphylococcus aureus strain exhibiting intermediate susceptibility in vitro to vancomycin (VISA). Neither vancomycin alone nor trovafloxacin exhibited in vivo efficacy; addition of amikacin to vancomycin yielded a modest in vivo effect. In contrast, the combination of ampicillin and sulbactam was highly effective in vivo, causing a mean decrease in VISA vegetation densities of >5 log(10) CFU/g versus those of untreated controls.

[Autologous osteochondral transplantation on various joints]

A chondral/osteochondral defect involving the articular surface of a joint is still a therapeutic problem. The goal of articular cartilage repair is restoration of cartilage congruity, accomplishing full painfree range of motion and elimination of cartilage detoriation. The use of autologous grafts was first reported by Wagner 1964. Now the use of cylindrical autograft plugs was described by Bobic 1996 and Hangody 1996. Operative management and early results of osteochondral cylindrical autograft plugs in the femoral condyle, patella, elbow and talar dome are presented. The arthroscopic/open use of autologous osteochondral grafts from the knee is indicated in osteochondral lesions in diameter from 1 to 3 cm, which can not be primarily refixed and in osteonecrosis at femoral condyle, patella, elbow, talar dome as well as shoulder.

[Transfer of the posterior femoral condyle. First experience with a salvage operation]

In this study large osteochondral defects on the weight-bearing surface of the medial and lateral femoral condyle were treated by transplantation of the autologous posterior condyle in 20 patients. The cartilage defects, type Outerbridge IV, ranged in size from 2 x 1.5 cm to 5 x 3.5 cm. 8 condyle transfers were done from 1984-1996 at the orthopaedic clinic of the university of Balgrist, Zürich. 12 condyle transfers at the department of orthopedic sports medicine at the technical university of Munich from 1996-1998. Patients were operated before the condyle transfer, 2 times on average. In 9 patients a high tibial osteotomy was performed simultaneously. Clinical evaluation was done according to the Lysholm score. The Lysholm score improved in the patient serie from 1996 from preoperatively 62 (54-81) points to postoperatively 85 (74-95) points. The follow-up was on average 9.8 (2-26) months. 18 patients reported about pain relief, 2 patients didn't improve. We describe the operative technique. Despite the lack of long-term results the transfer of the autologous posterior condyle seems to be an effective alternative for the knee prosthesis, especially for young patients with a great cartilage damage in the weight bearing area.