Involvement of the p38/MK2 Pathway in MCLR Hepatotoxicity Revealed through MAPK Pharmacological Inhibition and Phosphoproteomics in HepaRG Cells.

Microcystin-leucine arginine (MCLR) is one of the most common and toxic microcystin variants, a class of cyanotoxins produced by cyanobacteria. A major molecular mechanism for MCLR-elicited liver toxicity involves the dysregulation of protein phosphorylation through protein phosphatase (PP) inhibition and mitogen-activated protein kinase (MAPK) modulation. In this study, specific pharmacological MAPK inhibitors were used in HepaRG cells to examine the pathways associated with MCLR cytotoxicity. SB203580 (SB), a p38 inhibitor, rescued HepaRG cell viability, whereas treatment with SP600125 (JNK inhibitor), MK2206 (AKT inhibitor), or N-acetylcysteine (reactive oxygen species scavenger) did not. Phosphoproteomic analysis revealed that phosphosites-which were altered by the addition of SB compared to MCLR treatment alone-included proteins involved in RNA processing, cytoskeletal stability, DNA damage response, protein degradation, and cell death. A closer analysis of specific proteins in some of these pathways indicated that SB reversed the MCLR-mediated phosphorylation of the necroptosis-associated proteins, the mixed lineage kinase domain-like protein (MLKL), receptor-interacting serine/threonine kinase 1 (RIP1), DNA damage response proteins, ataxia telangiectasia and Rad3-related kinase (ATR), and checkpoint kinase 1 (CHK1). Overall, these data implicate p38/MK2, DNA damage, and necroptosis in MCLR-mediated hepatotoxicity, and suggest these pathways may be targets for prevention prior to, or treatment after, MCLR toxicity.

Glass microfluidic devices with thin membrane voltage junctions for electrospray mass spectrometry.

In this study a novel glass membrane was prepared for conducting high voltage (HV) to solution in the channel of a microfabricated device for generation of liquid electrospray. Taylor cone formation and mass spectra obtained from this microdevice confirmed the utility of the glass membrane, but voltage conduction through the membrane could not be successfully explained based solely on the conductivity of the glass itself. This novel method for developing a high-voltage interface for microdevices avoids direct metal/liquid contact eliminating bubble formation in the channel due to water hydrolysis on the surface of the metal. Further, this arrangement produces no dead volume as is often found with traditional liquid junctions. At the same time, preliminary investigations into the outlet design of glass microdevices for interfacing with electrospray mass spectrometry, was explored. Both the exit shape and the use of hydrophobic coatings at the channel exit of the microdevice electrospray interface were evaluated using standard proteins with results indicating the utility of this type of design after further optimization.

Protein digestion and phosphopeptide enrichment on a glass microchip.

This work describes an integrated glass microdevice for proteomics, which directly couples proteolysis with affinity selection. Initial results with standard phosphopeptide fragments from beta-casein in peptide mixtures showed selective capture of the phosphorylated fragments using immobilized metal affinity chromatography (IMAC) beads packed into a microchannel. Complete selectivity was seen with angiotensin, with capture of only the phosphorylated form. On-chip proteolysis, using immobilized trypsin beads packed into a separate channel, was directly coupled to the phosphopeptide capture and the integrated devices evaluated using beta-casein. Captured and eluted fragments were analyzed using both capillary electrophoresis (CE) and capillary liquid chromatography/mass spectrometry (cLC/MS). The results show selective capture of only phosphopeptide fragments, but incomplete digestion of the protein was apparent from multiple peaks in the CE separations. The MS analysis indicated a capture bias on the IMAC column for the tetraphosphorylated peptide fragment over the monophosphorylated fragment. Application to digestion and capture of a serum fraction showed capture of material; however, non-specific binding was evident. Additional work will be required to fully optimize this system, but this work represents a novel sample preparation method, incorporating protein digestion on-line with affinity capture for proteomic applications.