Functionally Integrated Top-Down Proteomics for Standardized Assessment of Human Induced Pluripotent Stem Cell-Derived Engineered Cardiac Tissues

Three-dimensional (3D) human induced pluripotent stem cell-derived engineered cardiac tissues (hiPSC-ECTs) have emerged as a promising alternative to two-dimensional hiPSC-cardiomyocyte monolayer systems because hiPSC-ECTs are a closer representation of endogenous cardiac tissues and more faithfully reflect the relevant cardiac pathophysiology. The ability to perform functional and molecular assessments using the same hiPSC-ECT construct would allow for more reliable correlation between observed functional performance and underlying molecular events, and thus is critically needed. Herein, for the first time, we have established an integrated method that permits sequential assessment of functional properties and top-down proteomics from the same single hiPSC-ECT construct. We quantitatively determined the differences in isometric twitch force and the sarcomeric proteoforms between two groups of hiPSC-ECTs that differed in the duration of time of 3D-ECT culture. Importantly, by using this integrated method we discovered a new and strong correlation between the measured contractile parameters and the phosphorylation levels of alpha-tropomyosin between the two groups of hiPSC-ECTs. The integration of functional assessments together with molecular characterization by top-down proteomics in the same hiPSC-ECT construct enables a holistic analysis of hiPSC-ECTs to accelerate their applications in disease modeling, cardiotoxicity, and drug discovery. Data are available via ProteomeXchange with identifier PXD022814.

Nanoproteomics enables proteoform-resolved analysis of low-abundance proteins in human serum

Top-down mass spectrometry (MS)-based proteomics provides a comprehensive analysis of proteoforms to achieve a proteome-wide understanding of protein functions. However, the MS detection of low-abundance proteins from blood remains an unsolved challenge due to the extraordinary dynamic range of the blood proteome. Here, we develop an integrated nanoproteomics method coupling peptide-functionalized superparamagnetic nanoparticles (NPs) with top-down MS for the enrichment and comprehensive analysis of cardiac troponin I (cTnI), a gold-standard cardiac biomarker, directly from serum. These NPs enable the sensitive enrichment of cTnI (<1 ng/mL) with high specificity and reproducibility, while simultaneously depleting highly abundant proteins such as human serum albumin (>1010 more abundant than cTnI). We demonstrate that top-down nanoproteomics can provide high-resolution proteoform-resolved molecular fingerprints of diverse cTnI proteoforms to establish proteoform-pathophysiology relationships. This scalable and reproducible antibody-free strategy can generally enable the proteoform-resolved analysis of low-abundance proteins directly from serum to reveal previously unachievable molecular details.

An Unbiased Proteomics Method to Assess the Maturation of Human Pluripotent Stem Cell-Derived Cardiomyocytes

RATIONALE

Human pluripotent stem cell (hPSC)-derived cardiomyocytes exhibit the properties of fetal cardiomyocytes, which limits their applications. Various methods have been used to promote maturation of hPSC-cardiomyocytes; however, there is a lack of an unbiased and comprehensive method for accurate assessment of the maturity of hPSC-cardiomyocytes.

OBJECTIVE

We aim to develop an unbiased proteomics strategy integrating high-throughput top-down targeted proteomics and bottom-up global proteomics for the accurate and comprehensive assessment of hPSC-cardiomyocyte maturation.

METHODS AND RESULTS

Utilizing hPSC-cardiomyocytes from early- and late-stage 2-dimensional monolayer culture and 3-dimensional engineered cardiac tissue, we demonstrated the high reproducibility and reliability of a top-down proteomics method, which enabled simultaneous quantification of contractile protein isoform expression and associated post-translational modifications. This method allowed for the detection of known maturation-associated contractile protein alterations and, for the first time, identified contractile protein post-translational modifications as promising new markers of hPSC-cardiomyocytes maturation. Most notably, decreased phosphorylation of α-tropomyosin was found to be associated with hPSC-cardiomyocyte maturation. By employing a bottom-up global proteomics strategy, we identified candidate maturation-associated markers important for sarcomere organization, cardiac excitability, and Ca²⁺ homeostasis. In particular, upregulation of myomesin 1 and transmembrane 65 was associated with hPSC-cardiomyocyte maturation and validated in cardiac development, making these promising markers for assessing maturity of hPSC-cardiomyocytes. We have further validated α-actinin isoforms, phospholamban, dystrophin, αB-crystallin, and calsequestrin 2 as novel maturation-associated markers, in the developing mouse cardiac ventricles.

CONCLUSIONS

We established an unbiased proteomics method that can provide accurate and specific assessment of the maturity of hPSC-cardiomyocytes and identified new markers of maturation. Furthermore, this integrated proteomics strategy laid a strong foundation for uncovering the molecular pathways involved in cardiac development and disease using hPSC-cardiomyocytes.

Abstract 405: Functional Maturation of Human iPSC-Derived Cardiomyocytes by Prolonged 3D Culture in Engineered Cardiac Tissue Constructs

The advent of human induced pluripotent stem cell (hiPSC) technology has revolutionized the way we study inherited diseases, as it allows us to study the effect of mutations in a human context. This is particularly true in the heart were species-specific differences has dramatic effects on heart rate, and expression of protein isoforms involved in excitation-contraction coupling. A major drawback of using hiPSCs is, however that cardiomyocytes derived from hiPSC (hiPSC-CM) are relatively immature, limiting their utility as a tool to study adult onset cardiac diseases.

We postulated that culturing hiPSC-CM in a 3D environment in engineered cardiac tissue constructs (ECT) would promote hiPSC-CM maturation.

ECTs were generated from lactate-selected day 30 hiPSCs that were mixed with isogenic hiPSC derived cardiac fibroblasts in a 10:1 ratio. Cells were mixed with fibrinogen and thrombin and seeded into molds under vacuum in FlexCell dishes to form ECT. ECTs were harvested 14-21 or 42-52 days later and subjected to functional testing, transcriptional analysis and top-down mass-spectrometry of sarcomeric proteins to assess maturation.

Functionally, we found that prolonged culture of hiPSCs in ECT resulted in increased calcium transient amplitude (0.856 vs. 0.462; P < 0.01) and an acceleration of calcium kinetics (calcium release time 67.7 ms vs. 109.3 ms; P < 0.01 and calcium decay time 148.3 ms vs. 188.0 ms; P < 0.05). This acceleration of calcium kinetics with time in culture was also true for twitch force kinetics (time to peak twitch force 178.6 ms vs. 208.0 ms; P < 0.05). Furthermore, beta adrenergic stimulation had a much greater effect on twitch kinetics in older ECTs (reduction in contraction time of 26.5% vs. 7.1%; P < 0.01). Transcriptional analysis revealed an increase in expression level of the beta 1 adrenergic receptor in older ECTs, while top-down mass spectrometry showed increased expression and phosphorylation of cardiac troponin I (cTnI) and mono-phosphorylated cTnI, as well as decreased phosphorylation of alpha-tropomyocin, all markers of myocardial maturation.

Taken together, these data supports our hypothesis that prolonged culture of hiPSC-CM in ECT promotes maturation of the calcium handling system and the contractile apparatus.

Simultaneous Quantification of Protein Expression and Modifications by Top-down Targeted Proteomics: A Case of the Sarcomeric Subproteome

Determining changes in protein expression and post-translational modifications (PTMs) is crucial for elucidating cellular signal transduction and disease mechanisms. Conventional antibody-based approaches have inherent problems such as the limited availability of high-quality antibodies and batch-to-batch variation. Top-down mass spectrometry (MS)-based proteomics has emerged as the most powerful method for characterization and quantification of protein modifications. Nevertheless, robust methods to simultaneously determine changes in protein expression and PTMs remain lacking. Herein, we have developed a straightforward and robust top-down liquid chromatography (LC)/MS-based targeted proteomics platform for simultaneous quantification of protein expression and PTMs with high throughput and high reproducibility. We employed this method to analyze the sarcomeric subproteome from various muscle types of different species, which successfully revealed skeletal muscle heterogeneity and cardiac developmental changes in sarcomeric protein isoform expression and PTMs. As demonstrated, this targeted top-down proteomics platform offers an excellent 'antibody-independent' alternative for the accurate quantification of sarcomeric protein expression and PTMs concurrently in complex mixtures, which is generally applicable to different species and various tissue types.

Abstract P2-18-07: Nipple sparing mastectomy-infectious complication risk. A preliminary assessment of the American Society of Breast Surgeons nipple sparing mastectomy registry

Objectives: The American Society of Breast Surgeons (ASBS) Nipple Sparing Mastectomy Registry (NSMR) is a prospective, IRB approved, non-randomized, multi-institutional registry assessing surgical techniques, utilized metrics, oncologic outcome, and aesthetic outcome of nipple sparing mastectomies. The registry has been open for enrollment for 26 months. The target accrual is 1000 individuals. This abstract specifically analyzes rates of post-operative infection in NSMs.

Methods: Fifty two investigators from 41 institutions are participating in the ASBS NSMR. A total of 373 patients underwent 631 mastectomies, with indications of prophylaxis (365), cancer (248), and unknown (18). We assessed a sub group of 449 mastectomies, with indications of prophylaxis (253) and cancer (196) that had all data sets completed. We assessed infection rates(characterized as needing oral or iv antibiotics with or without removal of implant/expander and/or debridement) in the entire group as well as by indication (cancer vs. prophylaxis). Factors such as smoking history, previous radiation therapy, previous surgery, incision type, reconstruction technique, and flap dissection technique were analyzed.

Results: In a subgroup of 449 mastectomies (253 prophylactic and 196 cancer):

Post operative infections were reported in 22 (4.9%) of patients: 7 (3.6%) of mastectomies with an indication of cancer and 15 (5.9%) of prophylactic mastectomies (p-value 0.3140). Infections were characterized as: treatment with oral antibiotics alone, treatment with i.v. antibiotics alone, iv antibiotics with washout or debridement, or antibiotics and implant/ tissue expander removal. No correlation was found in smoking history (p-value 1.000), previous breast surgery (p-value 0.1277) or previous radiation (p-value 0.6024). No correlation was found in incision utilized, reconstruction technique, or method of flap dissection either.

Conclusion:

The rate of postoperative infections in nipple sparing mastectomies is comparable if not lower than non-nipple sparing mastectomies. No statistically significant difference in infection rate was found between mastectomies completed for prophylaxis or cancer. No correlation was found between factors such as smoking history, history of radiation therapy, prior breast surgery, incision utilized, reconstruction technique, or method of flap dissection. Improved aesthetics with a nipple sparing approach (technically more demanding and typically through a smaller incision) does not come at the cost of a higher rate of infectious complications.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-18-07.

Identification by differential display of a protein phosphatase-2A regulatory subunit preferentially expressed in malignant melanoma cells

We described the occurrence of 4 transcripts differentially displayed between syngeneic murine B16F10 (metastatic melanoma) and Melan-a (immortalised melanocytes) cell lines. We now report that one such transcript, which is B16F10-specific, represents a protein phosphatase-2A B' regulatory subunit. No expression of this transcript was detected in the weakly metastatic B16F1 by Northern blotting. Moreover, the transcript was not expressed by spontaneously immortalised, non-tumorigenic, melanocytes (Melan-Ab and Melan-a2), nor was it expressed by ras-transformed, tumourigenic melanocytes (Melan-Ab-LTR-ras). Cloning of the 5'-end region of this transcript (termed band 8A) from B16F10 cells revealed an intracisternal A-particle insertion, including the long terminal repeat region, which could account for the observed high expression in B16F10 cells. Single cell clones of B16F10 manifested an experimental metastasis capacity, which correlated with band 8A expression with the lowest expressors being least metastatic. The human homologue of the B' regulatory subunit, B56gamma, is expressed preferentially at the mRNA level in human melanoma cell lines compared with normal epidermal melanocytes. In situ hybridisation studies on human clinical samples detected high expression of this gene in a number of malignant melanomas. Our results imply strongly that this protein phosphatase-2A regulatory subunit may have a role in melanoma tumour progression.

Identification by differential display of annexin-VI, a gene differentially expressed during melanoma progression

To identify genes involved in the melanocyte to malignant melanoma conversion, we have applied differential display to the comparison of syngeneic murine B16F10 (metastatic melanoma) and Melan-a-immortalized melanocyte cell lines. Approximately 7000 bands were analyzed, revealing approximately 80 to be differentially displayed. Reverse Northern blotting and subsequent Northern blotting confirmed the reproducible differential expression of four transcripts. Three B16F10-specific bands encode novel genes or partially sequenced cDNAs of unknown function. One Melan-a-specific band was found to be identical to the 3' end region of the mouse Annexin VI mRNA and shown to have a reduced message expression in B16F10 relative to Melan-a. Differential expression was confirmed at the protein level with Western blotting using a rabbit polyclonal antiserum. Immunohistochemistry of human melanoma specimens with this antiserum revealed a decrease or loss of Annexin VI expression as melanomas progressed from a benign to a more malignant phenotype. Our results provide further evidence for a potential role of Annexin VI in tumor suppression.

Veillonella myositis in an immunocompromised patient

Infectious myositis is rather uncommon. When caused by anaerobic organisms, myositis is usually polymicrobial. Trauma, ischemia, or a contiguous focus of infection is often an antecedent of myositis. We report a case of monomicrobial veillonella myositis in an immunocompromised patient. The infection responded to debridement and therapy with metronidazole.

Expression and function of the CD44 glycoprotein in melanoma cell lines

We have analysed a panel of murine and human melanoma cell lines for expression of the glycoprotein CD44. All 12 cell lines examined expressed CD44 at their cell surfaces, as demonstrated by fluorocytometric analysis using monoclonal antibodies (MAbs) IM7 and F10.44.2. Northern analysis revealed three transcript sizes that were 4.5, 2.2, and 1.5 kb in the human cell lines and 4.5, 3.0, and 1.5 kb in the murine cell lines. Levels of mRNA did not correlate with level of surface expression, which was highly variable between the cell lines. RT-PCR analysis of mRNA revealed that the major band identified was the expected 792 bp fragment indicative of the CD44H haemopoietic form, compared to a 1194 bp form found in the human colorectal adenocarcinoma cell line HT29, indicative of the CD44E epithelial form. There was no evidence of variant CD44 mRNA in our panel of melanomas. Functional assays revealed no clear correlation between the level of cell surface CD44 and the ability of the melanoma cell lines to adhere to hyaluronate. Rather adherence appeared to relate to the activation status of CD44 on the different cell lines as a consequence of MAb stimulation (e.g. the 1735P line demonstrated a 46.2 +/- 5.7% adherence in an inactivated state versus 62.4 +/- 5.6% adherence in an activated state to 5 mg/ml hyaluronate) and suggests that the functional capacity of CD44 expressed by melanoma cells may be modified more by activation state than by RNA splicing.

Planned early discharge from New Zealand maternity hospitals

AIMS

The purpose of the Plunket National Child Health Study was to establish a database on health indicators of New Zealand children and families. This paper examines the issue of early discharge in New Zealand maternity hospitals.

METHODS

As part of the study, 4286 parents were interviewed when the child was around six weeks post partum regarding their planned choice for length of post natal hospital stay and their actual length of stay.

RESULTS

Most New Zealand mothers choose to stay in hospital for 4-7 days following childbirth. Those mothers choosing early discharge (within 48 hours of delivery), tended to be multiparous, nonEuropean, less educated and of lower socioeconomic status.

CONCLUSIONS

The characteristics of those choosing early discharge demonstrate the vulnerability of this group and also have implications for the provision of health care services which are discussed.

An improved metaphase index assay for detecting thyroid growth stimulators using FRTL-5 thyroid cells cultured on a microtitre plate

The metaphase index assay (MIA) for thyroid growth stimulators, as originally described, used FRTL-5 thyroid cells cultured in Bellco culture chambers and glass microscope slides. The metaphases were observed using the nuclear strain aceto-lacto orcein. However the surface properties of the glass proved to be variable and so polystyrene microscope slides were substituted. The aceto-lacto orcein stain was found to be unsuitable for use with polystyrene because of the solvents and mountant used. Therefore combinations of various other nuclear stains and mounting media were tested. The Giemsa stain, which was found to be the most satisfactory, could be applied to FRTL-5 cells maintained on the large variety of plastic supports now available for tissue culture, e.g., 96 well microtitre plates. This permitted the design of an MIA which is much more convenient, robust and economical in its use of clinical samples. The results with seven IgG preparations derived from the sera of patients with a variety of thyroid disorders are presented. In its revised form, the metaphase index assay provides a rapid screening assay for thyroid growth stimulators, such as autoantibodies and TSH.

Recovery of plant amines with carboxylic ion-exchange substrates and their subsequent analysis by thin-layer chromatography

Two grades of carboxymethylcellulose (CMC) and five ion-exchange resins were compared for their effectiveness in recovering endogenous amines from plant extracts. If amine loss was to be limited to 10%, the H+ and Na+ forms of CMC could not be loaded with the solutes from more than 0.25 and 1.5 gram fresh weight (gfw) tissue per ml bed volume respectively. The corresponding ionic forms of a typical resin, Amberlite CG-50, would tolerate loadings ca. 5 X higher than this. However, it was then necessary to use very slow flow-rates (13 ml cm-2 h-1) for both applying and eluting the amines and, even so, they could not be quantitatively displaced from any resin tested, with the possible exception of Duolite C433. If the extract was acidic, maximum permissible loadings were reduced by a factor of 3 to 20, depending on substrate and ionic form. The composition of the amine fraction was essentially the same whatever substrate was used for its recovery and whatever percentage of it had been lost.

Enhanced 3-methoxytyramine levels in crown gall tumours and other undifferentiated plant tissues

An amine, after dansylation, has been isolated from Nicotiana tabacum crown gall tumours for the first time and characterized as 4-hydroxy-3-methoxy-beta-phenylethylamine (3-methoxytyramine). The compound cannot be detected in differentiated N. tabacum tissues but appears in the corresponding callus controls. Its concentration is further increased 5-42-fold when N. tabacum is transformed with all strains of Agrobacterium tumefaciens so far tested.