Getting started with CEAS

Setup

library(ceas)

Importing Seahorse rates data

The read_data function takes a list of Excel files. An easy way to get such a list is to put all your data in a directory and list its contents. Here we use the package’s internal datasets, but list.files will take a directory name as its first argument.

rep_list <- system.file("extdata", package = "ceas") |>
  list.files(pattern = "*.xlsx", full.names = TRUE)
raw_data <- readxl::read_excel(rep_list[1], sheet = 2)
knitr::kable(head(raw_data))

Measurement	Well	Group	Time	OCR	ECAR	PER
1	A01	Background	1.304765	0.0000	0.00000	0.0000
1	A02	Group_1 MITO	1.304765	305.2426	30.64529	334.4771
1	A03	Group_1 MITO	1.304765	307.9862	33.27668	358.4754
1	A04	Group_2 MITO	1.304765	339.3399	49.17751	503.4910
1	A05	Group_2 MITO	1.304765	321.9398	47.94602	492.2597
1	A06	Group_2 MITO	1.304765	323.7962	46.84232	482.1940

The data requires the following columns: Measurement, Well, Group, Time, OCR, ECAR, PER. The Group column needs to be in the format biological_group<space>Assay_type as shown above. Upon reading with read_data, the Group column is split into two group and assay columns on the space. This output format can be set in the Seahorse machine before starting the experiment. If you already have the data, this column will have to be converted to this format to work with ceas.

seahorse_rates <- read_data(rep_list)
knitr::kable(head(seahorse_rates))

Measurement	Well	Time	OCR	ECAR	PER	exp_group	assay_type	replicate
1	A01	1.304765	0.0000	0.00000	0.0000	Background	NA	1
1	A02	1.304765	305.2426	30.64529	334.4771	Group_1	MITO	1
1	A03	1.304765	307.9862	33.27668	358.4754	Group_1	MITO	1
1	A04	1.304765	339.3399	49.17751	503.4910	Group_2	MITO	1
1	A05	1.304765	321.9398	47.94602	492.2597	Group_2	MITO	1
1	A06	1.304765	323.7962	46.84232	482.1940	Group_2	MITO	1

Normalization

There are two types of normalization involved in Seahorse data analysis. One is background normalization done by the Wave software. ceas will produce a warning if it finds that the “Background” data are not 0 (see first row of the table above).

The other is biological normalization based on the cell count or the mass of protein. If the data is not already biologically normalized, you will need a csv file containing experimental groups and cell counts or $\mu$g of protein in this format:

norm_csv <- system.file("extdata", package = "ceas") |>
  list.files(pattern = "norm.csv", full.names = TRUE)
read.csv(norm_csv) |> knitr::kable()

exp_group	measure
Group_1	30000
Group_2	30000
Group_3	5000
Group_4	5000

Your csv file’s full path may be passed into read_data() using the norm argument.

read_data(rep_list, norm = norm_csv) |> head() |> knitr::kable()

Measurement	Well	Time	OCR	ECAR	PER	exp_group	assay_type	replicate
1	A01	1.304765	0.00000	0.000000	0.00000	Background	NA	1
1	A02	1.304765	50.87376	5.107549	55.74619	Group_1	MITO	1
1	A03	1.304765	51.33103	5.546114	59.74590	Group_1	MITO	1
1	A04	1.304765	56.55665	8.196252	83.91516	Group_2	MITO	1
1	A05	1.304765	53.65663	7.991003	82.04329	Group_2	MITO	1
1	A06	1.304765	53.96603	7.807053	80.36566	Group_2	MITO	1

Calculating energetics

Partitioning data

Note:
When we use the term ‘max’ in the package documentation we mean the maximal experimental OCR and ECAR values rather than absolute biological maximums.

The energetics calculation workflow involves partitioning the data into its time point and assay intervals.

partitioned_data <- partition_data(seahorse_rates)

Alternative data formats

While the default options are set for an experiment with both a mitochondrial and glycolysis assay, if you have only a mitochondrial assay or no glycolysis assay, the assay_types list parameter can be modified to account for that.

• Mito + Glyco (our default)
• Data in the form of Mookerjee et al. (2017)
• Just Mito
• Respiratory control ratio (RCR) and glycolytic capacity (GC) assay

partitioned_data <- partition_data(
  seahorse_rates,
  assay_types = list(
    basal = "MITO",
    uncoupled = "MITO",
    maxresp = "MITO",
    nonmito = "MITO",
    no_glucose_glyc = "GLYCO",
    glucose_glyc = "GLYCO",
    max_glyc = "GLYCO"
  ),
  basal_tp = 3,
  uncoupled_tp = 6,
  maxresp_tp = 8,
  nonmito_tp = 12,
  no_glucose_glyc_tp = 3,
  glucose_glyc_tp = 6,
  max_glyc_tp = 8
)

partitioned_data <- partition_data(
  seahorse_rates,
  assay_types = list(
    basal = "RefAssay",
    uncoupled = "RefAssay",
    maxresp = NA,
    nonmito = "RefAssay",
    no_glucose_glyc = "RefAssay",
    glucose_glyc = "RefAssay",
    max_glyc = NA
  ),
  basal_tp = 5,
  uncoupled_tp = 10,
  nonmito_tp = 12,
  maxresp = NA,
  no_glucose_glyc_tp = 1,
  glucose_glyc_tp = 5,
  max_glyc = NA
)

partitioned_data <- partition_data(
  seahorse_rates,
  assay_types = list(
    basal = "MITO",
    uncoupled = "MITO",
    maxresp = "MITO",
    nonmito = "MITO",
    no_glucose_glyc = NA,
    glucose_glyc = "MITO",
    max_glyc = NA
  ),
  basal_tp = 3,
  uncoupled_tp = 6,
  maxresp_tp = 8,
  nonmito_tp = 12,
  no_glucose_glyc_tp = NA,
  glucose_glyc_tp = 3,
  max_glyc_tp = NA
)

partitioned_data <- partition_data(
  seahorse_rates,
  assay_types = list(
    basal = "RCR",
    uncoupled = "RCR",
    maxresp = "RCR,"
    nonmito = "RCR",
    no_glucose_glyc = NA,
    glucose_glyc = "GC",
    max_glyc = "GC"
  ),
  basal_tp = 3,
  uncoupled_tp = 6,
  maxresp_tp = 8,
  nonmito_tp = 12,
  no_glucose_glyc = NA,
  glucose_glyc_tp = 3,
  max_glyc_tp = 9
)

Note that the time point parameters (maxresp_tp and no_glucose_glyc_tp) also need to be changed accordingly.

The get_energetics function requires pH, pK$_a$ and buffer values.

energetics <- get_energetics(partitioned_data, ph = 7.4, pka = 6.093, buffer = 0.10)

For more information on the calculations see the article on ATP calculations.

Plotting

Bioenergetic scope plot

The bioscope_plot function plots a 2D representation of group “bioenergetic scope.” Bioenergetic scope describes the theoretical energetic space in which a matrix operates. The bioenergetic scope coordinates are JATP from OXPHOS on the y-axis and JATP from glycolysis on the x-axis. The points represent mean basal and/or max JATP from OXPHOS and glycolysis and the vertical and horizontal lines represent the standard deviation or confidence interval of JATP from OXPHOS or glycolysis, respectively.

(bioscope <- bioscope_plot(energetics))

Rate plots

The rate_plot function provides an overview of OCR or ECAR for each assay type over time, which enables cross-group energetic comparisons before and after the addition of energetic-modulating compounds. The rate_plot line represents mean group OCR or ECAR over the sequential measurements (x-axis) and the shaded variance region represents standard deviation or specified confidence interval.

• Oxygen consumption rate (OCR)
• Extracellular Acidification Rate (ECAR)

(ocr <- rate_plot(seahorse_rates, measure = "OCR", assay = "MITO"))

(ecar <- rate_plot(seahorse_rates, measure = "ECAR", assay = "GLYCO"))

ATP plots

The atp_plot function plots group JATP values, which enables cross-group OXPHOS and glycolytic JATP comparisons at basal and max conditions. The atp_plot symbols represent the mean basal or max JATP from OXPHOS or glycolysis, and the crossbar boundaries represent the standard deviation or confidence interval JATP variance.

• Basal glycolysis
• Basal respiration
• Maximal glycolysis
• Maximal respiration

(basal_glyc <- atp_plot(energetics, basal_vs_max = "basal", glyc_vs_resp = "glyc"))

(basal_resp <- atp_plot(energetics, basal_vs_max = "basal", glyc_vs_resp = "resp"))

(max_glyc <- atp_plot(energetics, basal_vs_max = "max", glyc_vs_resp = "glyc"))

(max_resp <- atp_plot(energetics, basal_vs_max = "max", glyc_vs_resp = "resp"))

Customizing plots

CEAS is designed to work with existing ggplot2 customization functionality and doesn’t include more than shape and size options for its plots.

For example, to change the colors used in the plot, simply make the plot and add the custom colors you’d like:

Colors

custom_colors <- c("#e36500", "#b52356", "#3cb62d", "#328fe1")

bioscope +
ggplot2::scale_color_manual(
  values = custom_colors
)

ocr +
ggplot2::scale_color_manual(
  values = custom_colors
)

Labels

• Change axis labels
• Change label size

ecar +
    ggplot2::labs(x = "Time points")

basal_glyc +
    ggplot2::theme(axis.text = ggplot2::element_text(size = 20))

Editing functions

We are working on making the plots as customizable as possible. However, if there are options that cannot be set in the calls to the plotting functions or with ggplot2 functions, you can get the code used to make the plots by running the function name without parenthesis and modify it. Further, since every step in the ceas workflow provides a dataset, you can run the modified function or your own custom plotting functions on those datasets.

rate_plot

function (seahorse_rates, measure = "OCR", assay = "MITO", error_bar = "ci", 
    conf_int = 0.95, group_label = "Experimental group") 
{
    stopifnot(`'measure' should be 'OCR' or 'ECAR'` = measure %in% 
        c("OCR", "ECAR"))
    stopifnot(`'error_bar' should be 'sd' or 'ci'` = error_bar %in% 
        c("sd", "ci"))
    stopifnot(`'conf_int' should be between 0 and 1` = conf_int > 
        0 && conf_int < 1)
    data_cols <- c("Measurement", "Well", "OCR", "ECAR", "PER", 
        "exp_group", "assay_type", "replicate")
    missing_cols <- setdiff(data_cols, colnames(seahorse_rates))
    if (length(missing_cols) != 0) {
        stop(paste0("'", missing_cols, "'", " column was not found in input data\n"))
    }
    Measurement <- NULL
    exp_group <- NULL
    lower_bound <- NULL
    upper_bound <- NULL
    plot_data <- get_rate_summary(seahorse_rates, measure, assay, 
        error_bar, conf_int)
    y_labels <- list(OCR = paste0(assay, " OCR (pmol/min)"), 
        ECAR = paste0(assay, " ECAR (mpH/min)"))
    ggplot(plot_data, aes(x = Measurement, y = mean, color = exp_group, 
        group = exp_group, fill = exp_group)) + geom_line(size = 2) + 
        geom_ribbon(aes(ymin = lower_bound, ymax = upper_bound), 
            alpha = 0.2, color = NA) + scale_x_continuous(breaks = seq(1, 
        12, by = 1)) + xlab("Measurement") + ylab(y_labels[measure]) + 
        labs(color = group_label, fill = group_label) + theme_bw()
}

In RStudio, you can run utils::edit to modify a function.

edit(rate_plot)

References

Mookerjee, Shona A., Akos A. Gerencser, David G. Nicholls, and Martin D. Brand. 2017. “Quantifying Intracellular Rates of Glycolytic and Oxidative ATP Production and Consumption Using Extracellular Flux Measurements.” Journal of Biological Chemistry 292 (17): 7189–7207. https://doi.org/10.1074/jbc.M116.774471.