Ryanodine Receptor Glycation Favors Mitochondrial Damage in the Senescent Heart

BACKGROUND

Senescent cardiomyocytes exhibit a mismatch between energy demand and supply that facilitates their transition toward failing cells. Altered calcium transfer from sarcoplasmic reticulum (SR) to mitochondria has been causally linked to the pathophysiology of aging and heart failure.

METHODS

Because advanced glycation-end products accumulate throughout life, we investigated whether intracellular glycation occurs in aged cardiomyocytes and its impact on SR and mitochondria.

RESULTS

Quantitative proteomics, Western blot and immunofluorescence demonstrated a significant increase in advanced glycation-end product-modified proteins in the myocardium of old mice (≥20months) compared with young ones (4-6months). Glyoxalase-1 activity (responsible for detoxification of dicarbonyl intermediates) and its cofactor glutathione were decreased in aged hearts. Immunolabeling and proximity ligation assay identified the ryanodine receptor (RyR2) in the SR as prominent target of glycation in aged mice, and the sites of glycation were characterized by quantitative mass spectrometry. RyR2 glycation was associated with more pronounced calcium leak, determined by confocal microscopy in cardiomyocytes and SR vesicles. Interfibrillar mitochondria-directly exposed to SR calcium release-from aged mice had increased calcium content compared with those from young ones. Higher levels of advanced glycation-end products and reduced glyoxalase-1 activity and glutathione were also present in atrial appendages from surgical patients ≥75 years as compared with the younger ones. Elderly patients also exhibited RyR2 hyperglycation and increased mitochondrial calcium content that was associated with reduced myocardial aerobic capacity (mitochondrial O₂ consumption/g) attributable to less respiring mitochondria. In contracting HL-1 cardiomyocytes, pharmacological glyoxalase-1 inhibition recapitulated RyR2 glycation and defective SR-mitochondria calcium exchange of aging.

CONCLUSIONS

Mitochondria from aging hearts develop calcium overload secondary to SR calcium leak. Glycative damage of RyR2, favored by deficient dicarbonyl detoxification capacity, contributes to calcium leak and mitochondrial damage in the senescent myocardium.

Akt regulation of glycolysis mediates bioenergetic stability in epithelial cells

Cells use multiple feedback controls to regulate metabolism in response to nutrient and signaling inputs. However, feedback creates the potential for unstable network responses. We examined how concentrations of key metabolites and signaling pathways interact to maintain homeostasis in proliferating human cells, using fluorescent reporters for AMPK activity, Akt activity, and cytosolic NADH/NAD⁺ redox. Across various conditions, including glycolytic or mitochondrial inhibition or cell proliferation, we observed distinct patterns of AMPK activity, including both stable adaptation and highly dynamic behaviors such as periodic oscillations and irregular fluctuations that indicate a failure to reach a steady state. Fluctuations in AMPK activity, Akt activity, and cytosolic NADH/NAD⁺ redox state were temporally linked in individual cells adapting to metabolic perturbations. By monitoring single-cell dynamics in each of these contexts, we identified PI3K/Akt regulation of glycolysis as a multifaceted modulator of single-cell metabolic dynamics that is required to maintain metabolic stability in proliferating cells.

Linear Integration of ERK Activity Predominates over Persistence Detection in Fra-1 Regulation

ERK signaling regulates the expression of target genes, but it is unclear how ERK activity dynamics are interpreted. Here, we investigate this question using simultaneous, live, single-cell imaging of two ERK activity reporters and expression of Fra-1, a target gene controlling epithelial cell identity. We find that Fra-1 is expressed in proportion to the amplitude and duration of ERK activity. In contrast to previous "persistence detector" and "selective filter" models in which Fra-1 expression only occurs when ERK activity persists beyond a threshold duration, our observations demonstrate that the network regulating Fra-1 expression integrates total ERK activity and responds to it linearly. However, exploration of a generalized mathematical model of the Fra-1 coherent feedforward loop demonstrates that it can perform either linear integration or persistence detection, depending on the basal mRNA production rate and protein production delays. Our data indicate that significant basal expression and short delays cause Fra-1 to respond linearly to integrated ERK activity.

Abstract B1-30: Receptor-level feedback mechanisms distinguish frequency- and amplitude-modulated ERK activation

Receptor tyrosine kinases transduce signals through ERK and drive distinct cellular behaviors, but it is not clear how dynamic patterns of ERK activity are generated. To approach this question quantitatively, we have generated an epithelial cell line expressing a tunable version of the canonical nerve growth factor (NGF) receptor TrkA. Upon NGF stimulation, we visualized the dynamics of ERK activity in live cells using an improved fluorescent reporter for ERK activity, EKAR3. Examination of the NGF receptor pathway in isolation revealed that stimulation with NGF promotes a prolonged ERK activity pulse that is amplitude-modulated by the concentration of the stimulus, in contrast to the frequency modulation observed in the epidermal growth factor (EGF)-RAS-ERK pathway. This result implies that the primary determinants of ERK kinetics are the unique set of signaling proteins recruited to the activating receptor. To dissect the context in which ERK is activated in respect to parallel signaling pathways, we have engineered mutant NGF receptors that cannot be phosphorylated at one or more of the three adaptor binding sites and characterized how each signaling pathway contributes to the pattern of dynamic ERK activity. Furthermore, because our NGF receptor expression system allows the tunable and quantifiable expression of receptor levels, we have evaluated the effect of receptor number on ERK kinetics in single cells. Our findings indicate that the dynamics of ERK activity are in fact decided at the receptor-level and may explain how different receptor tyrosine kinase profiles in cancer cells modulate distinct patterns of ERK activity.

Citation Format: Breanne Sparta, Michael Pargett, Kevin Distor, Marta Minguet, John G. Albeck. Receptor-level feedback mechanisms distinguish frequency- and amplitude-modulated ERK activation. [abstract]. In: Proceedings of the AACR Special Conference on Computational and Systems Biology of Cancer; Feb 8-11 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 2):Abstract nr B1-30.

Abstract B2-38: Learning the dynamic response to Ras-ERK signaling with paired reporters

To characterize key cell signaling pathways in cancer, we employ a modular strategy to examine how signals propagate between two members in a pathway, using paired time series measurements in live cells. The two pathway members chosen bracket a sub-network for which we measure input and output signals. In this study, we characterize models for the response of FRA1 (Fos related antigen 1) to ERK (extracelluar regulated kinase) activity. Mathematical response models are constrained by the paired signal data to produce a predictive module for the ERK-to-FRA1 sub-network, complementing existing modeling efforts as a building block for complete models.

Background: Many mutations in cancer impair cellular information processing by hyperactivating signaling pathways associated with proliferation and migration. However, targeted inhibitors for hyperactivated elements have not yielded consistent responses, and acquired resistance hinders their use in therapy. Cell signaling can be a complex dynamic process [1], the detailed understanding of which will support development of new research directions and clinical therapies.

The Ras-ERK signaling pathway regulates cell proliferation and migration, and is often mutated in cancer. ERK activity (the nominal pathway output) regulates major drivers of cell decision making, such as the transcription factor FRA1 which is involved in migration and invasion [2]. FRA1 is observed being regulated by ERK at three levels: (1) transcription via ERK-dependent phosphorylation of transcription factors; (2) translation via promotion of mTORC1 (mammalian target of rapamycin complex 1), and (3) stability via ERK-dependent phosphorylation of a c-terminal destabilization motif. The interplay of multiple regulation points in this feed-forward manner may lead to complex responses, including behavior as a ‘persistence detector’ for ERK activity, where only long term activity produces strong responses because short pulses fail to stabilize the protein.

Experimental method: To make paired measurements, we generate a cell line expressing both a fluorescent reporter for ERK activity, and a fluorescent FRA1 fusion protein on the genomic locus. Cells are treated with varied levels of extracellular ligands and therapeutic drugs to elicit varied ERK responses, and time series images taken for up to 72 hours. Segmentation and particle tracking yield individual cell time courses over the length of the experiment.

Modeling: Models of the FRA1 response to ERK activity are considered at several levels of abstraction to evaluate the complexity of the response against a mechanistic model. The most parsimonious model, that which satisfies data with the least complexity, can then predict FRA1 levels based on ERK activity, with minimal bias from overfitting. Fitting individual cell time courses produces the distribution of cell responses over populations.

Conclusions: The characterized response models demonstrate the predictive capacity for FRA1 from ERK activity, revealing that the responsiveness to ERK varies from cell to cell. Over the cell populations observed, the models capture the distribution of the response. These models augment the existing body of work describing the ERK activity resulting from receptor stimulation, and may be further combined with future modular models toward a predictive global model.

References:

[1] Albeck JG, Mills GB, Brugge JS (2013) Frequency-modulated pulses of ERK activity transmit quantitative proliferation signals. Molecular cell, 49(2), 249-261.

[2] Dhillon AS, Tulchinsky E (2014) FRA-1 as a driver of tumour heterogeneity: a nexus between oncogenes and embryonic signalling pathways in cancer. Oncogene, doi: 10.1038/onc.2014.374.

Citation Format: Michael Pargett, Marta Minguet, Kevin Distor, John G. Albeck. Learning the dynamic response to Ras-ERK signaling with paired reporters. [abstract]. In: Proceedings of the AACR Special Conference on Computational and Systems Biology of Cancer; Feb 8-11 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 2):Abstract nr B2-38.

Receptor Level Mechanisms Are Required for Epidermal Growth Factor (EGF)-stimulated Extracellular Signal-regulated Kinase (ERK) Activity Pulses

In both physiological and cell culture systems, EGF-stimulated ERK activity occurs in discrete pulses within individual cells. Many feedback loops are present in the EGF receptor (EGFR)-ERK network, but the mechanisms driving pulsatile ERK kinetics are unknown. Here, we find that in cells that respond to EGF with frequency-modulated pulsatile ERK activity, stimulation through a heterologous TrkA receptor system results in non-pulsatile, amplitude-modulated activation of ERK. We further dissect the kinetics of pulse activity using a combination of FRET- and translocation-based reporters and find that EGFR activity is required to maintain ERK activity throughout the 10-20-minute lifetime of pulses. Together, these data indicate that feedbacks operating within the core Ras-Raf-MEK-ERK cascade are insufficient to drive discrete pulses of ERK activity and instead implicate mechanisms acting at the level of EGFR.

Changes in cervicocephalic kinesthesia after a proprioceptive rehabilitation program in patients with neck pain: a randomized controlled study

Head repositioning accuracy (HRA) after full range active motion was evaluated in 60 cervicalgic patients. The mean angular error was 7.7 degrees +/- 3.3 (mean +/- SD) and 82% were outside a threshold value of 4.5 degrees. After randomization 30 patients followed a rehabilitation program based on eye-head coupling (RG) and 30 served as a control group (CG). At 10 week follow-up, a greater gain in HRA was observed in the RG (2 degrees +/- 2.7, mean +/- SD) than in the CG (0 +/- 2.6, mean +/- SD) (p = 0.005). Clinical parameters (pain, drug intake, range of motion, and self assessed functional improvement) were also more improved in the RG than in the CG. These data emphasize the role of a neck proprioception alteration in chronic neck pain and suggest that a rehabilitation program based on eye-head coupling should be included in most medical management of cervicalgic patients.

Cervicocephalic kinesthetic sensibility in patients with cervical pain

Head orientation in space makes use of multiple sensory afferents, among which the cervical proprioceptive cues could play a predominant role. To quantify the alteration of neck proprioception in patients with cervical pathology, we proposed a test for the clinical evaluation of the ability to relocate the head on the trunk after an active head movement, for 30 healthy subjects and 30 patients with cervical pain. The data demonstrated that this ability was significantly poorer in the patient group, indicating an alteration in neck proprioception. This test permits a discriminant classification of healthy and sick subjects, justifies proprioceptive rehabilitation programs, and allows a quantitative evaluation of their results.