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Improved identification of proteoforms using FAIMS with internal CV stepping in top-down proteomics

ABSTRACT: In top-down (TD) proteomics, fractionation prior to mass spectrometric (MS) analysis is a crucial step for the high confidence identification of proteoforms and increased sample depth. In addition to liquid phase separations, gas-phase fractionation strategies such as field asymmetric ion mobility spectrometry (FAIMS) have been shown to be highly beneficial in TD proteomics. However, the need for multiple injections using different compensation voltages (CV) leads to a huge increase in measurement time and the amount of sample required. Therefore, we here investigated for the first time the use of internal CV stepping for single shot TD analysis, i.e., the application of multiple CVs per acquisition. In addition, MS parameters were optimized for the individual CVs since different CVs target certain mass ranges. For example, small proteoforms identified mainly with lower CVs can be identified with a lower resolution and number of microscans than larger proteins identified mainly with higher CVs. We investigated the optimal combination and number of CVs for different gradient lengths and validated the optimized settings with the low molecular weight proteome of CaCo 2 cells obtained by different sample preparation techniques. Compared to measurements without FAIMS, both the number of identified protein groups (+60-94%) and proteoforms (+46-127%), and their confidence were significantly increased, while the measurement time remained identical. In total, we identified 684 protein groups and 2,675 proteoforms from CaCo-2 cells in less than 24 hours using the optimized multi-CV method.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture, Colon

DISEASE(S): Colon Cancer

SUBMITTER: Andreas Tholey

LAB HEAD: Andreas Tholey

PROVIDER: PXD029792 | Pride | 2022-02-28

REPOSITORIES: Pride

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Project description:Episodes of chronic stress can result in psychic disorders like post-traumatic stress disorder, but also promote the development of metabolic syndrome and type 2 diabetes. We hypothesize that muscle, as main regulator of whole-body energy expenditure, is a central target of acute and adaptive molecular effects of stress in this context. Here, we investigate the immediate effect of a stress period on energy metabolism in Musculus gastrocnemius in our established C57BL/6 chronic variable stress (Cvs) mouse model. Cvs decreased lean body mass despite increased energy intake, reduced circadian energy expenditure (EE), and substrate utilization. Cvs altered the proteome of metabolic components but not of the oxidative phosphorylation system (OXPHOS), or other mitochondrial structural components. Functionally, Cvs impaired the electron transport chain (ETC) capacity of complex I and complex II, and reduces respiratory capacity of the ETC from complex I to ATP synthase. Complex I-OXPHOS correlated to diurnal EE and complex II-maximal uncoupled respiration correlated to diurnal and reduced nocturnal EE. Bioenergetics assessment revealed higher optimal thermodynamic efficiencies (ƞ-opt) of mitochondria via complex II after Cvs. Interestingly, transcriptome and methylome were unaffected by Cvs, thus excluding major contributions to supposed metabolic adaptation processes. In summary, the preclinical Cvs model shows that metabolic pressure by Cvs is initially compensated by adaptation of mitochondria function associated with high thermodynamic efficiency and decreased EE to manage the energy balance. This counter-regulation of mitochondrial complex II may be the driving force to longitudinal metabolic changes of muscle physiological adaptation as the basis of stress memory.Chronic stress targets mitochondrial respiratory efficiency in the skeletal muscle of C57BL/6 mice.Nikolic A, Fahlbusch P, Wahlers N, Riffelmann NK, Jacob S, Hartwig S, Kettel U, Dille M, Al-Hasani H, Kotzka J, Knebel B. Cell Mol Life Sci. 2023 Mar 29;80(4):108. doi: 10.1007/s00018-023-04761-4.PMID: 36988756

Project description:Chronic stress leads post-traumatic stress disorder (PTSD) and to metabolic complications, including fatty liver. It is feasible, that stress immediately initiates molecular mechanisms to alter energy metabolism and glucose homeostasis which interfere with hepatic lipid accumulation after stress recovery. We aim to elucidate these molecular mechanisms of long term stress effects on metabolism and focus on physiological adaptation and the role of FGF21, which is protective in hepatic lipid accumulation. Methods FGF21 knockout and control mice were exposed to chronic variable stress (Cvs) and recovered for 3 months to simulate PTSD. We determined in vivo and ex vivo energy metabolism, mitochondrial function by extracellular flux analysis, alterations in DNA modifying enzymes and gene regulation immediately after stress and after the recovery period to determine long term alterations. Results Chronic stress leads to reduced insulin sensitivity and hepatic lipid accumulation with increased fatty acid uptake (FAU), stress-induced lipolysis, and reduction in NAD+/NAD ratio and Sirt activity. Immediately after stress, PPARa and SREBP-1 target genes are differentially regulated and are involved in the development of stress-induced fatty liver. After recovery, insulin sensitivity increases but insulin-induced de novo lipogenesis (DNL) is reduced and FAU is increased. HDAC and MT activity are suppressed, whereas HAT activity increases, linking metabolic adjustments to transcriptional regulators. Thus, key metabolic genes are differentially regulated and secreted proteins indicate the activation of liver disease by Cvs only in FGF21WT. GR binding to the Cd36 promoter is altered. After stress recovery, serum FGF21 is increased and protects against lipid accumulation. FGF21 interacts by attenuating DNL, increasing FAU and HAT activity, and balancing mitochondrial activity. Higher long-term stress-induced activation and binding of GR to the FGF21 promoter may contribute to the prolonged FGF21 release. Conclusions We show that previous stress exposure determines predisposition to fatty liver disease is regulated by FGF21. Immediately after Cvs, altered gene regulation and activity of DNA-modifying enzymes determine the metabolic late effects seen in PTSD. FGF21 functions after chronic stress exposure i) to protect against hepatic lipid accumulation, ii) to maintain mitochondrial capacity, and iii) to mediate in the modulation of DNA-modifying enzymes. These findings highlight the protective role of FGF21 even in stress-induced hepatic lipid accumulation.

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Improved identification of proteoforms using FAIMS with internal CV stepping in top-down proteomics

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