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Representative Results






Fiber Type Identification of Human Skeletal Muscle

Published: September 22nd, 2023



1Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, School of Agriculture, Biomedicine and Environment, La Trobe University
* These authors contributed equally

This protocol demonstrates single-fiber isolation from freeze-dried human skeletal muscle and fiber-type classification according to Myosin heavy chain (MHC) isoform using the dot blotting technique. Identified MHC I and II fiber samples can then be further analyzed for fiber type-specific differences in protein expression using western blotting.

The technique described here can be used to identify specific myosin heavy chain (MHC) isoforms in segments of individual muscle fibers using dot blotting, hereafter referred to as Myosin heavy chain detection by Dot Blotting for IDentification of muscle fiber type (MyDoBID). This protocol describes the process of freeze-drying human skeletal muscle and isolating segments of single muscle fibers. Using MyDoBID, type I and II fibers are classified with MHCI- and IIa-specific antibodies, respectively. Classified fibers are then combined into fiber type-specific samples for each biopsy.

The total protein in each sample is determined by Sodium Dodecyl-Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) and UV-activated gel technology. The fiber type of samples is validated using western blotting. The importance of performing protein loading normalization to enhance target protein detection across multiple western blots is also described. The benefits of consolidating classified fibers into fiber type-specific samples compared to single-fiber western blots, include sample versatility, increased sample throughput, shorter time investment, and cost-saving measures, all while retaining valuable fiber type-specific information that is frequently overlooked using homogenized muscle samples. The purpose of the protocol is to achieve accurate and efficient identification of type I and type II fibers isolated from freeze-dried human skeletal muscle samples.

These individual fibers are subsequently combined to create type I and type II fiber type-specific samples. Furthermore, the protocol is extended to include the identification of type IIx fibers, using Actin as a marker for fibers that were negative for MHCI and MHCIIa, which are confirmed as IIx fibers by western blotting. Each fiber type-specific sample is then used to quantify the expression of various target proteins using western blotting techniques.

Skeletal muscle is a heterogeneous tissue, with distinct cellular metabolic and contractile properties that are dependent on whether the cell (fiber) is slow twitch (type I) or fast twitch (type II). The fiber type can be identified by examining the myosin heavy chain (MHC) isoforms, which differ from each other in several ways, including contraction time, speed of shortening, and fatigue resistance1. Major MHC isoforms include type I, type IIa, type IIb, and type IIx and their metabolic profiles are either oxidative (type I and IIa) or glycolytic (IIx, IIb)1. The proportion of these fiber types varies in muscle type and....

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Human muscle samples were obtained from the vastus lateralis from n = 3 (2 males, 1 female), aged 70-74 years old under sterile conditions using local anesthesia (Xylocaine) and a Bergstrom needle modified for manual suction11,12. Samples were a subset of a previous study approved by the Victoria University Human Research Ethics Committee (HRETH11/221) and conducted in accordance with the Declaration of Helsinki13. Participants pr.......

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Identification of individual MHCI, MHCIIa, and MHCIIx muscle fibers using dot blotting
A feature of MyDoBID is the categorization of the varying MHC and Actin signal intensity strength in a given fiber (Figure 4A). Fiber type was identified by the presence or absence of MHCI and IIa isoforms (Figure 4B). Six fibers showed no MHC or actin detection, indicating that there was no fiber collected. The results of this specific dot blot were the.......

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Fiber collection
Based on several years of experience, most researchers can master this technique; however, practice leads to faster and more efficient fiber collection for downstream analyses. To be able to isolate 30 single fiber segments of a quality for pooling, it is recommended that 50 fiber segments are collected per sample. Studying the fiber collection video carefully and after performing two practice sessions (~50 fibers per session) is recommended to achieve a reasonable standard. All fi.......

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The antibodies against MHC I (A4.840) and MHCIIa (A4.74) used in this study were developed by Dr. H. M. Blau and the antibody against MHCIIx (6H1) was developed by Dr. C. A. Lucas and obtained from the Developmental Studies Hybridoma Bank (DSHB), thanks to the auspices of the National Institute of Child Health and Human Development and maintained by the University of Iowa, Department of Biological Sciences (Iowa City, IA). We thank Victoria L. Wyckelsma for providing the human muscle samples for this study. The majority of the images in Figure 1 was sourced from

This study received no external ....

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Name Company Catalog Number Comments
1x Denaturing buffer Make according to recipe Constituents can be sourced from Sigma-Aldrich or other chemical distributing companies  1x denaturing buffer is made by diluting 3x denaturing buffer 1 in 3 v/v with 1X Tris-HCl (pH 6.8). Store at -20 °C.
3x Denaturing buffer Make according to recipe Constituents can be sourced from Sigma-Aldrich or other chemical distributors 3x denaturing buffer contains: 0.125M Tris-HCI, 10% glycerol, 4% SDS, 4 M urea, 10% 2-mercaptoethanol, and 0.001% bromophenol blue, pH 6.8.  Store at -20 °C.
95% Ethanol N/A 100% ethanol can be sourced from any company Diluted to 95% with ultra-pure H2O.
Actin rabbit polyclonal antibody Sigma-Aldrich   A2066 Dilute 1 in 1,000 with BSA buffer.
Analytical scales Mettler Toledo Model number: MSZ042101
Antibody enhancer Thermo Fischer Scientific 32110 Product name is Miser Antibody Extender Solution NC.
Beaker (100 mL) N/A N/A
Benchtop centrifuge Eppendorf 5452 Model name: Mini Spin.
Blocking buffer: 5% Skim milk in Wash buffer. Diploma Store bought
BSA buffer: 1 % BSA/PBST, 0.02 % NaN3 BSA: Sigma-Aldrich              PBS: Bio-Rad Laboratories. NaN3 : Sigma-Aldrich  BSA: A6003-25G                         10x PBS: 1610780                       NaN3: S2002 Bovine serum albumin (BSA), Phosphate-buffered saline (PBS), and Sodium azide (NaN3). Store at 4 °C.
Cassette opening lever  Bio-Rad Laboratories 4560000 Used to open the precast gel cassettes.
Chemidoc MP Imager  Bio-Rad Laboratories Model number: Universal hood III Any imaging system with Stain-Free gel imaging capabilities.
Criterion blotter Bio-Rad Laboratories 1704070 Includes ice pack, transfer tray, roller, 2 cassette holders, filter paper, foam pads and lid with cables.
Criterion Cell (Bio-Rad) Bio-Rad Laboratories 1656001
ECL (enhanced chemiluminescence) Bio-Rad Laboratories 1705062 Product name: Clarity Max Western ECL Substrate.
Electrophoresis buffer 1x Tris Glycine SDS (TGS) Bio-Rad Laboratories 1610772 Dilute 10x TGS 1 in 10 with ultra-pure H2O.
Filter paper, 0.34 mm thick Whatmann 3030917 Bulk size 3 MM, pack 100 sheets, 315 x 335 mm.
Fine tissue dissecting forceps Dumont F6521-1EA Jeweller’s forceps no. 5.
Flat plastic tray/lid   N/A N/A Large enough to place the membrane on. Ensure the surface is completely flat.
Freeze-drying System Labconco 7750030 Freezone 4.5 L with glass chamber sample stage.
Freezer -80 o N/A N/A Any freezer with a constant temperature of -80 °C is suitable.
Gel releasers 1653320 Bio-Rad Slide under the membrane to gather or move the membrane.
Grey lead pencil N/A N/A
 Image lab software  Bio-Rad Laboratories N/A Figures refers to software version 5.2.1 but other versions can used.
Incubator Bio-Rad Laboratories 1660521 Any incubator that can be set to 37 °C would suffice.
Lamp N/A N/A
Magnetic stirrer with flea N/A N/A
Membrane roller  Bio-Rad Laboratories 1651279 Can be purchased in the Transfer bundle pack. However, if this product is not available, any smooth surface cylindrical tube long enough to roll over the membrane would suffice. 
Microcentrifuge tubes  (0.6 mL) N/A N/A
Mouse IgG HRP secondary Thermo Fisher Scientific 31430 Goat anti-Mouse IgG (H+L), RRID AB_228341. Dilute at 1 in 20,000 in blocking buffer.
Mouse IgM HRP secondary Abcam ab97230 Goat Anti-Mouse IgM mu chain. Use at the same dilution as mouse IgG.
Myosin Heavy Chain I (MHCI) primary antibody DSHB A4.840  Dilution range: 1 in 200 to 1 in 500 in BSA buffer.
Myosin Heavy Chain IIa (MHCIIa) primary antibody DSHB A4.74  Dilution range: 1 in 200 to 1 in 500 in BSA buffer.
Myosin Heavy Chain IIx (MHCIIx) primary antibody DSHB 6H1 Dilution range: 1 in 200 to 1 in 500 in BSA buffer.
Nitrocellulose Membrane 0.45 µm  Bio-Rad Laboratories 1620115 For Western blotting.
Petri dish lid N/A N/A
Plastic tweezers N/A N/A
Power Pack  Bio-Rad Laboratories 164-5050 Product name: Basic power supply.
Protein ladder Thermo Fisher Scientific 26616 PageRuler Prestained Protein Ladder, 10 to 180 kDa.
PVDF Membrane 0.2 µm Bio-Rad Laboratories 1620177
Rabbit HRP secondary Thermo Fisher Scientific 31460 Goat anti-Rabbit IgG (H+L), RRID AB_228341. Dilution same as mouse secondary antibodies.
Rocker N/A N/A
Ruler N/A N/A
Scissors N/A N/A
Stereomicroscope Motic SMZ-168
Stripping buffer Thermo Fisher Scientific 21059 Product name: Restore Western Blot Stripping Buffer.
Tissue (lint free) Kimberly-Clark professional 34120 Product name: Kimwipe.
Transfer buffer (1x Tris Glycine buffer (TG), 20% Methanol) TG: Bio-Rad Laboratories   Methanol: Merck TG buffer: 1610771           Methanol: 1.06018 dilute 10x TG buffer with ultra-pure H2O to 1x. Add 100% Methanol to a final concentration of 20% Methanol. Store at 4 °C.
Transfer tray Bio-Rad Laboratories 1704089
 UV-activation precast gel Bio-Rad Laboratories 5678085 Gel type: 4–15% Criterion TGX Stain-Free Protein Gel, 26 well, 15 µL.
Vortex N/A N/A
Wash buffer (1x TBST) 10x TBS: Astral Scientific  Tween 20: Sigma  BIOA0027-4L 1x TBST recipe: 10x Tris-buffered saline (TBS) is diluted down to 1x with ultra-pure H2O, Tween 20 is added to a final concentration of 0.1%. Store buffer at 4 °C.
Wash containers Sistema Store bought Any tupperware container, that suits the approximate dimensions of the membrane would suffice.

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