Impact of TIEG1 Deletion on the Passive Mechanical Properties of Fast and Slow Twitch Skeletal Muscles in Female Mice

Abstract

As transforming growth factor (TGF)-β inducible early gene-1 is highly expressed in skeletal muscle, the effect of TIEG1 gene deletion on the passive mechanical properties of slow and fast twitch muscle fibers was analyzed. Twenty five muscle fibers were harvested from soleus (Sol) and extensor digitorum longus (EDL) muscles from TIEG1-/- (N = 5) and control (N = 5) mice. Mechanical tests were performed on fibers and the dynamic and static stresses were measured. A viscoelastic Hill model of 3rd order was used to fit the experimental relaxation test data. In parallel, immunohistochemical analyses were performed on three serial transverse sections to detect the myosin isoforms within the slow and fast muscles. The percentage and the mean cross sectional area of each fiber type were calculated. These tests revealed a significant increase in the mechanical stress properties for the TIEG1-/- Sol fibers while a significant decrease appeared for the TIEG1-/- EDL fibers. Hill model tracked the shape of the experimental relaxation curve for both genotypes and both fiber types. Immunohistochemical results showed hypertrophy of all fiber types for TIEG1-/- muscles with an increase in the percentage of glycolytic fibers (IIX, and IIB) and a decrease of oxidative fibers (I, and IIA). This study has provided new insights into the role of TIEG1, known as KLF10, in the functional (SoltypeI: more resistant, EDLtypeIIB: less resistant) and morphological (glycolytic hypertrophy) properties of fast and slow twitch skeletal muscles. Further investigation at the cellular level will better reveal the role of the TIEG1 gene in skeletal muscle tissue.

Fig 1. Representative force-length curve measurement.

Hysteresis ΔA (hatched area) was calculated as the difference between the areas under the extension curve ① (arrow from left to right) and the de-stretch curve ② (arrow from right to left).

Fig 2. Normalized hysteresis ± SEM values measured after the two preconditioning tests performed on Sol and EDL fibers for each genotype.

Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1.

Fig 3. Experimental mechanical behavior of the Sol and EDL fibers, for each genotype, after a ramp stretch.

The static stress (σs) was measured at the end of the stretch. Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1.

Fig 4. Experimental representations of the dynamic (σd) and static (σs) stresses obtained during the relaxation test performed on TIEG1^-/^- and WT muscle fibers (Sol, EDL).

Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1.

Fig 5. Comparison of experimental and numerical viscoelastic behaviors using a 3rd order Hill model for TIEG1^-/^- and WT fibers (Sol, EDL).

Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1.

Fig 6. (A) Sol and (B) EDL fiber areas (mean ± SEM) for TIEG1^-/^- and WT mice.

Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1. Signification:*: P<0.05; **: P<0.01.

Fig 7. Percentage of fiber type (I, IIA, IIB, IIX) within Sol (A) and EDL (B) muscles for both genotypes (TIEG1^-/^-,WT). Representation of the fiber types through immunohistological staining.

Soleus: Sol, extensor digitorum longus: EDL, WT: wild type, TIEG1^-/^-: Transforming Growth Factor β inducible early gene-1. Signification: *: P<0.05; **: P<0.01; NS: Not significant; t: Tendency.