Genomics & Pharmacogenomics

Biography

Biography: Günter Müller

Abstract

Most conventional approaches toward biomarker identification have failed to provide tools that would enable to stratify cellular stress responses and pave the way for a more personalized medicine for stress-related diseases, such as type 2 diabetes (T2D). We are therefore taking an entirely different path relying on novel technology and a minimal (biophysical) bias. We established and validated a chip-based biosensor based on the principle of surface acoustic waves (SAW) which enables characterization and quantification of extracellular complexes in plasma. These harbor glycosylphosphatidylinositol-anchored proteins (GPI-APs) and phospholipids (ECGAPP). ECGAPP have already been shown to be released from the surface of metabolically relevant cells through non-classical secretory mechanisms in response to metabolic stress as is prevalent during T2D. Importantly, ECGAPP are assumed to differ in level, morphology, structure and biophysical properties between distinct states of (metabolic) stress. Strikingly, GPI-APs have been shown to exhibit high susceptibility for release in ECGAPP from the surface of mammalian cells in response to T2D. The presence of ECGAPP in body fluids of stressed people has not been studied so far, possibly due to conceptual (reductionistic and causal thinking) and technological limitations. To overcome these hurdles, the SAW biosensor will be used for the specific detection and biophysical characterization of ECGAPP. Any specific interaction of ECGAPP with the gold surface via the capturing molecule alpha-toxin and the monitoring molecule annexin-V (for the detection of phospholipids) will result in corresponding changes in the shape of the SAW, altering both their phase and amplitude and thereby reflecting changes in mass loading and biophysical properties. The data indicate that the time-resolved signatures recorded in course of successive binding and releasing of ECGAPP to the chip surface in the presence of differential concentrations of synthetic phosphoinositolglycans (PIG), that interfere with the specific interaction of the core glycan portion of the GPI anchors contained in the ECGAPP and alpha-toxin, differ significantly between sera from wildtype and ZF (either normal or obese) rats with regard to amplitude reductions and between wildtype and ZDF (either normal and obese) rats with regard to phase shifts. Trends in either amplitude reductions or phase shifts were measured between sera from normal and obese ZF rats, normal and obese ZDF obese rats, normal and obese wildtype rats as well as betwee normal ZF and ZDF rats. Measurement of phase shifts and amplitude reductions of SAW exposed to complexes, which interact with the biosensor chip surface via GPI-APs and phospholipids as their constituents as a minimal bias, was sufficient to differentiate between sera from normal and (pre-)diabetic rats on the basis of mass reflecting differences in the amount of ECGAPP released and their putative post-translational modifications as well as on the basis of viscoelasticity reflecting alterations in the spatial configuration and conformation of the ECGAPP constituents. The requirement for the presence of limiting concentrations of PIG, that compete for the interaction of the ECGAPP with the chip, indicate that a subset of ECGAPP is relevant for the successful differentiation, only, rather than that the differentiating signatures represent a summation signal over all ECGAPP released. This phenomenological approach may open new avenues for biomarker research for and the prediction of common diseases since it does not depend on knowledge of the underlying molecular basis for the monitored differences in the ECGAPP signatures a priori as is the case for conventional reductionistic and causal approaches.