Wheat-Germ-Agglutinin Cross-Sectional Morphometry of Cardiomyocyte Hypertrophy in Transverse Aortic Constriction (TAC) Mouse Myocardium

Mice (e.g., C57BL/6J males, 10-12 weeks) are randomized to TAC or sham surgery (n≥8/group to allow for surgical attrition; final analysis n≥6). Pressure gradient is confirmed by Doppler echocardiography 3-7 days post-op; animals not achieving a target gradient are excluded a priori. Hearts are harvested at a fixed endpoint (e.g., 4 weeks). From each heart, ≥3 mid-ventricular sections are stained; ≥100-150 qualifying myocytes per heart (transverse, single central nucleus, intact membrane) are measured. All imaging and measurement are performed blinded to surgical group.

Animal work requires IACUC approval; TAC is a survival surgery demanding trained personnel, aseptic technique, analgesia, and appropriate anesthesia/monitoring. PFA is a fixative and probable carcinogen — handle in a fume hood with gloves; collect PFA waste as hazardous chemical waste. WGA is a lectin (mild irritant); DAPI is a potential mutagen — handle with gloves and dispose appropriately. Sharps (cryostat/microtome blades, surgical instruments) require sharps containers. PPE: lab coat, nitrile gloves, eye protection. Biological tissue waste follows institutional protocols.

Sham-surgery control: mice undergoing identical thoracotomy without aortic banding control for surgical stress and define baseline CSA. Staining control: a no-WGA (DAPI-only) section confirms membrane signal specificity; a secondary/autofluorescence control confirms signal is WGA-derived. Orientation control: only transversely cut, centrally nucleated myocytes are measured (oblique/longitudinal cuts excluded) — a built-in measurement control against angle artifact. Organ-level control: heart-weight/body-weight (or /tibia-length) ratio independently corroborates hypertrophy. Blinding control: section coding ensures the measurer cannot infer group.

Sham LV myocytes typically have CSA in the ~150-250 µm² range; 4-week TAC induces a 30-100% increase in mean CSA with a clear rightward shift of the distribution. Heart-weight/tibia-length ratio increases in TAC. WGA outlines appear as continuous bright sarcolemmal rings around polygonal myocytes with a central DAPI nucleus. Well-banded animals show consistent hypertrophy; failed bands (low gradient) appear sham-like and are excluded. Fetal genes (Nppa, Myh7) are induced in TAC by qPCR if assessed.

• C57BL/6J mice, 10-12 weeks (institutional IACUC-approved)
• Tissue fixative: 4% paraformaldehyde (PFA) in PBS, or OCT for cryosections
• Sucrose 30% (cryoprotection) for frozen sections; or paraffin processing reagents
• WGA conjugate, e.g., WGA-Alexa Fluor 488 (Thermo W11261), working 5-10 µg/mL
• DAPI nuclear counterstain, 1 µg/mL
• PBS (pH 7.4), blocking buffer (1% BSA), antifade mounting medium (e.g., ProLong Gold)
• Microscope slides, coverslips, charged slides for sections
• Cryostat or microtome; standard histology consumables
• (Optional) Doppler echocardiography ultrasound gel and depilatory cream

To quantify cardiomyocyte hypertrophy in mouse left-ventricular myocardium following pressure overload by transverse aortic constriction (TAC) versus sham surgery, using fluorescent wheat-germ-agglutinin (WGA) to outline myocyte sarcolemma in tissue sections and automated measurement of cross-sectional area (CSA) on transversely cut, centrally nucleated myocytes.

1. Confirm TAC gradient by echocardiography 3-7 days post-surgery; exclude animals below the target peak velocity/gradient threshold.
2. At endpoint, euthanize per IACUC, excise the heart, record heart weight, body weight, and tibia length; arrest in cold KCl/cardioplegia if assessing relaxed dimensions.
3. Fix in 4% PFA (or embed in OCT and freeze); cut 5-8 µm transverse mid-ventricular sections.
4. (Paraffin) deparaffinize/rehydrate; (cryo) post-fix briefly. Wash 3x in PBS.
5. Incubate sections with WGA conjugate (5-10 µg/mL) in PBS for 1 h at room temperature, protected from light.
6. Wash 3x in PBS; counterstain nuclei with DAPI (1 µg/mL, 5 min); wash and mount with antifade medium.
7. Image at 20-40x on a fluorescence/confocal microscope, acquiring multiple non-overlapping LV free-wall fields per section with identical exposure.
8. Measure CSA only on myocytes cut in true transverse orientation (roughly circular outline) with a single central nucleus and continuous WGA membrane outline.

Independent variable: surgical group (TAC vs sham) and endpoint duration. Dependent variables: myocyte cross-sectional area (µm²), CSA distribution, heart-weight/tibia-length ratio, and (optional) fetal-gene qPCR. Controlled variables: mouse strain/sex/age, section thickness (5-8 µm), section location (mid-ventricular LV free wall), WGA concentration and incubation time, imaging magnification/exposure, myocyte inclusion criteria (transverse, central nucleus, intact membrane), and number of cells measured per heart. Echo-confirmed gradient controls for surgical efficacy.

Chronic pressure overload from TAC will induce concentric cardiomyocyte hypertrophy, manifesting as a significantly increased mean myocyte cross-sectional area and a rightward shift in the CSA distribution relative to sham-operated controls, accompanied by increased heart-weight-to-body-weight (or tibia-length) ratio and induction of fetal-gene markers (Nppa/Nppb, Myh7).

WGA-bordered transverse myocytes are segmented in ImageJ/Fiji (threshold the WGA channel, watershed-separate, measure area) or with automated tools (e.g., MyoVision, CellProfiler) using the central-nucleus and circularity criteria to filter qualifying cells. ≥100-150 myocytes per heart are measured; the per-heart mean CSA is the experimental unit. Distributions are plotted as histograms/violin plots per group. Heart-weight ratios and qPCR (ΔΔCt vs sham, normalized to a stable reference gene) are tabulated alongside.

1. Faint/uneven WGA outlines: under-staining or thick sections — increase WGA to 10 µg/mL, extend incubation, and cut thinner (5 µm) sections. 2. Cannot find transverse myocytes: oblique sectioning plane — re-orient embedding to the LV short axis and section mid-ventricle. 3. High measurement variance: too few cells or inconsistent inclusion criteria — measure ≥100-150 qualifying (transverse, central-nucleus) myocytes per heart and standardize the segmentation threshold. 4. No hypertrophy difference: ineffective banding — verify the echo gradient and exclude low-gradient animals before analysis. 5. Membrane signal merges between adjacent cells: over-staining/poor separation — apply watershed segmentation and tighten the WGA threshold, or reduce WGA concentration.

Per-heart mean CSA is compared between TAC and sham by a two-tailed unpaired t-test (Welch's if variances differ) or Mann-Whitney if non-normal (Shapiro-Wilk), with the heart as the experimental unit (n≥6/group) to avoid pseudoreplication of individual myocytes. Distribution shifts are tested by Kolmogorov-Smirnov. Heart-weight ratios use the same framework. For multiple time points, two-way ANOVA with Sidak correction. Power analysis (detect ~30% CSA increase, SD≈20%, 80% power, α=0.05) supports n≈6-8/group, with surgical attrition built into the initial n.