Specific Antibody Production by Blood B Cells is Retained in Late Stage Drug-naïve HIV-infected Africans

Unseparated peripheral blood mononuclear cells (PBMCs) obtained from drug-naïve African individuals living in a context of multi-infections and presenting with high viral load (VL), were cultured in vitro and tested for their ability to produce antibodies (Abs) reacting with HIV-1 antigens. Within these PBMCs, circulating B cells were differentiated in vitro and produced IgG Abs against not only ENV, but also GAG and POL proteins. Under similar experimental conditions, HAART treated patients produced Abs to ENV proteins only. The in vitro antibody production by drug-naïve individuals' PBMCs depended on exogenous cytokines (IL-2 and IL-10) but neither on the re-stimulation of reactive cells in cultures by purified HIV-1-gp 160 antigen nor on the re-engagement of CD40 surface molecules. Further, it was not abrogated by the addition of various monoclonal Abs (mAbs) to co-stimulatory molecules. This suggests that the in vitro antibody production by drug-naïve individuals' PBMCs resulted from the maturation of already envelope and core antigen-primed, differentiated B cells, presumably pre-plasma cells, which are not known to circulate at homeostasy. As in vitro produced Abs retained the capacity of binding antigen and forming complexes, this study provides pre-clinical support for functional humoral responses despite major HIV- and other tropical pathogen-induced B cell perturbations

A united statement of the global chiropractic research community against the pseudoscientific claim that chiropractic care boosts immunity.

BACKGROUND: In the midst of the coronavirus pandemic, the International Chiropractors Association (ICA) posted reports claiming that chiropractic care can impact the immune system. These claims clash with recommendations from the World Health Organization and World Federation of Chiropractic. We discuss the scientific validity of the claims made in these ICA reports. MAIN BODY: We reviewed the two reports posted by the ICA on their website on March 20 and March 28, 2020. We explored the method used to develop the claim that chiropractic adjustments impact the immune system and discuss the scientific merit of that claim. We provide a response to the ICA reports and explain why this claim lacks scientific credibility and is dangerous to the public. More than 150 researchers from 11 countries reviewed and endorsed our response. CONCLUSION: In their reports, the ICA provided no valid clinical scientific evidence that chiropractic care can impact the immune system. We call on regulatory authorities and professional leaders to take robust political and regulatory action against those claiming that chiropractic adjustments have a clinical impact on the immune system

Insight into muscle physiology through understanding mechanisms of muscle pathology

International audienc

Regional variation in myofilament length-dependent activation.

International audienceThe Frank-Starling law is an important regulatory mechanism of the heart that links the end-diastolic volume with the systolic ejection fraction. This beat-to-beat regulation of the heart, underlined at the cellular level by higher myofilament calcium sensitivity at longer sarcomere length, is known as length-dependent activation or stretch sensitization of activation. However, the heart is structurally and functionally heterogeneous and asymmetrical. Specifically, contractile properties are not uniform within the left ventricle partly due to transmural differences in action potential waveforms and calcium homeostasis. The present review will focus on the role of the contractile machinery in the transmural contractile heterogeneity and its adaptation to changes in muscle strain. The expression of different myosin isoforms, the level of titin-based passive tension, and thin and thick sarcomeric regulatory proteins are considered to explain the regional cellular contractile properties. Finally, the importance of transmural heterogeneity of length-dependent activation and the consequences of its modification on the heart mechanics are discussed. Despite extensive research since the characterization of the Frank-Starling law, the molecular mechanisms by which strain information is transduced to the contractile machinery have not been fully determined yet

Some rat: A very special rat with a rather special titin

International audienceEditorial Some rat: A very special rat with a rather special titin Cycling cross-bridges, the molecular interactions between the contractile proteins actin and myosin, generate the muscle force that underlies cardiac pressure development. In striated muscle, these proteins are organized in the thick and thin filaments that together form the sarcomere. A more recent discovery localizes a third filament to the sarcomere, one that is composed of titin. Titin, also known as connectin, is a giant protein (3–4 MDa) that is an abundant protein in striated muscle forming up to 10% of the total protein content of the cardiac cell. Titin extends half the length of the sarcomere from the Z-disc through the I-band and A-band on to the M-line (~1 μm). The molecule is tightly anchored at its NH 2-terminus in the Z-disk via interactions with alpha-actinin and at its C-terminal domain to the M-line via interactions with myosin. The cell biology of titin has been the subject of intense study by several groups following its discovery in the seventies [1,20]. It was immediately recognized that a significant function of titin in the sarcomere might be structural. Indeed, titin has emerged as the main cellular structure responsible for passive striated muscle cell stiffness [2,3]. Furthermore, within the physiological range of cardiac volume, titin appears to be responsible for a significant portion of the diastolic passive filling pressure of the heart; the remainder of the elastic force being generated by extra-cellular matrix collagen [4]. The elasticity of titin originates within the I-band portion due to the presence of i) tandem immunoglobulin (Ig) repeats, ii) a region rich in proline (P), glutamate (E), valine (V), and lysine (K), the PEVK region and iii) a region with a sequence unique to cardiac titin, the N2B region. Alternative splicing provides additional tandem Ig repeats that insert between the N2B and PEVK regions. These longer titin isoforms also have an N2A region and are termed N2BA. In a sarcomere at slack length, titin is highly folded with many of the regions acting as entropic springs. As the sarcomere is stretched, the links between the tandem Ig repeats extend first, followed by PEVK unfolding and finally N2B region unfolding at the upper end of the physiological range of sarcomere lengths. The tandem Ig repeats are thought to unfold only beyond the non physiological range of sarcomere lengths and forces [2,3]. It has become increasingly clear recently that titin's functions are far more complex and that this giant molecule may play a much larger role in striated muscle physiology than merely as a passive stress bearing protein. For example, it has been suggested that titin plays an important role in regulating both protein turnover and gene expression in response to mechanical strain [2,3]. Moreover, the protein itself is a kinase capable, at least in-vitro, of phosphorylating telethonin (T-cap), a titin capping protein located at the Z-disk region of titin. However, whether this actually occurs in vivo is not clear since titin's kinase domain is physically far removed from the T-cap substrate

Couplage excitation-métabolisme-contraction dans le coeur sain et insuffisant (mécanismes physiopathologiques, influence d'une pollution atmosphérique et stratégies préventives)

Bien que les progrès thérapeutiques aient permis de freiner la progression des maladies cardio-vasculaires (CV), mais surtout d'améliorer leur prévention et par conséquent de réduire la survenue d'accidents CV, ces maladies devraient rester les premières causes mondiales de décès dans les prochaines années. Cet état des lieux épidémiologique illustre donc des insuffisances concernant à la fois la prévention, mais également la prise en charge du risque CV. Ce travail de thèse s'est alors intéressé à la compréhension des mécanismes physiopathologiques de l'insuffisance cardiaque ischémique (ICi), maladie CV la plus répandue, afin de proposer des stratégies préventives limitant le remodelage cardiaque délétère ; ainsi qu'à l'étude de la pollution atmosphérique comme potentiel facteur de risque CV. Le couplage excitation-métabolisme-contraction (E-M-C), qui sous-tend la fonction de la pompe cardiaque, s'adapte en réponse à différents stimuli par une modification des interrelations spatiales et temporelles complexes entre activités électriques, énergétiques et mécaniques. Ces modifications à différents niveaux peuvent initier un remodelage délétère évoluant vers une altération du fonctionnement, voire une défaillance chronique, du myocarde.Ce travail de thèse met en évidence un découplage entre les activités mitochondriales et contractiles, à l'origine d'un déséquilibre des homéostasies ioniques et redox, responsables des dysfonctions cardiaques étudiées dans des contextes d'ICi et d'exposition en milieu pollué au CO. Ainsi, une approche thérapeutique, visant à restaurer les fonctions mitochondriales et à rétablir le couplage E-M-C cardiaque, pourrait être considérée afin de préserver au mieux la fonction myocardique. Ce travail de thèse permet alors une meilleure compréhension des mécanismes physiopathologiques de l'ICi, et identifie la pollution atmosphérique comme facteur de risque CV à considérer en clinique afin de mieux prévenir le risque CV.Abstract non available.MONTPELLIER-BU Médecine UPM (341722108) / SudocSudocFranceF

Effets de différents stress physio/pathologiques sur l'activation des myofilaments à travers la paroi du ventricule gauche de différentes espèces

MONTPELLIER-BU Médecine UPM (341722108) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Length–Tension Relationships of Sub-epicardial and Sub-endocardial Single Ventricular Myocytes from Rat and Ferret Hearts

International audienceIn vivo the sub-epicardial myocardium (EPI) and sub-endocardial myocardium (ENDO) operate over different ranges of sarcomere length (SL). However, it has not been previously shown whether EPI and ENDO work upon different ranges of the same or differing length–tension curves. We have compared the SL–tension relationship of intact, single ventricular EPI and ENDO myocytes from rat and ferret hearts. Cells were attached to carbon fibres of known compliance in order to stretch them and to record force at rest (passive tension) and during contractions (active tension). In both species, ENDO cells were significantly stiffer (i.e. had steeper SL–passive tension relationships) than EPI cells. Ferret ENDO cells had significantly steeper SL–active tension relationships than EPI cells; rat cells tended to behave similarly but no significant regional differences in active properties were observed. There were no inter-species differences in the active and passive properties of EPI cells, but ferret ENDO cells displayed significantly steeper passive and active SL–tension relationships than rat ENDO. We conclude that in vivo, ferret EPI and ENDO myocytes will function over different ranges of different SL–tension curves. There is a close relationship between SL and active tension (the Frank–Starling law of the heart), and our observations suggest that regional differences in the response to ventricular dilation will depend on both the change in SL and differing regional slopes of the SL–active tension curves

Titin-Based Modulation of Calcium Sensitivity of Active Tension in Mouse Skinned Cardiac Myocytes Materials and Methods Preparations and Solutions

International audienceWe studied the effect of titin-based passive force on the length dependence of activation of cardiac myocytes to explore whether titin may play a role in the generation of systolic force. Force-pCa relations were measured at sarcomere lengths (SLs) of 2.0 and 2.3 m. Passive tension at 2.3 m SL was varied from 1 to 10 mN/mm 2 by adjusting the characteristics of the stretch imposed on the passive cell before activation. Relative to 2.0 m SL, the force-pCa curve at 2.3 m SL and low passive tension showed a leftward shift (pCa 50 [change in pCa at half-maximal activation]) of 0.090.02 pCa units while at 2.3 m SL and high passive tension the shift was increased to 0.250.03 pCa units. Passive tension also increased pCa 50 at reduced interfilament lattice spacing achieved with dextran. We tested whether titin-based passive tension influences the interfilament lattice spacing by measuring the width of the myocyte and by using small-angle x-ray diffraction of mouse left ventricular wall muscle. Cell width and interfilament lattice spacing varied inversely with passive tension, in the presence and absence of dextran. The passive tension effect on length-dependent activation may therefore result from a radial titin-based force that modulates the interfilament lattice spacing. (Circ Res. 2001;88:1028-1035.

Is titin the length sensor in cardiac muscle? Physiological and physiopathological perspectives.

International audienceOne of the most salient physiological characteristics of cardiac muscle is that a dilated heart pumps more vigorously, a phenomenon known as the Frank-Starling relationship (see Allen and Kentish, 1985). At least two cellular mechanisms participate in this phenomenon: the reduction of the interfilament lattice spacing which favors the formation of cross-bridges (Wang and Fuchs, 1995) and the increased affinity of troponin C (TnC) for calcium (Ca2+) (Babu et al., 1988). In the latter case, it has been established that TnC itself is not the length sensor (Moss et al., 1991). The intracellular structure(s) able to sense changes in cell length has always been challenged and is still not known. We previously observed on intact isolated cardiac cells that active tension is more closely related to passive tension than to sarcomere length per se (Cazorla et al., 1997). This might have some physiological implications in the working heart since we found that sub-epicardial cells are more supple than sub-endocardial cells. In the present work on skinned cells, we studied the relationship between different levels of passive tension (modulated by a mild trypsin digestion) and the shift in pCa50 of tension-pCa relations induced by a stretch of cells from 1.9 to 2.3 microns sarcomere length. A significant correlation was obtained between passive tension and the stretch-induced shift in pCa50, or stretch-sensitivity of the active force. These observations led us to assume that titin might play a role in sensing cell length to modulate the contractile activity. Besides, it is known that myocardial infarcted cells are less sensitive to stretch. We propose that, in such a rat model, alterations of titin might participate in heart failure