PMC:3681796 / 20374-25008 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/3681796","sourcedb":"PMC","sourceid":"3681796","source_url":"http://www.ncbi.nlm.nih.gov/pmc/3681796","text":"SCD1 knockout mice do not manifest motor impairment but display exacerbated muscle metabolic oxidative capacity\nTo gain insight into the way in which the lack of SCD1 expression impacts on muscle function, we investigated several characteristics of muscles in these SCD1 knockout mice reflecting their metabolic status, and also evaluated their motor behavior. At the molecular level, we measured the expression of PGC1-α, PPARα and PDK4, of which an increase is involved in stimulating mitochondrial biogenesis and in switching the energy source from glucose to fatty acids [22]. The expression of these genes was significantly higher in the gastrocnemius of SCD1 knockout mice, as compared to wild-type littermates; in the tibialis anterior, there was also a trend toward an increased expression (Figure 3A). Despite this latter attenuated response, the tibialis anterior represents, better than the gastrocnemius, a typical example of glycolytic muscle in which to evaluate changes in the relative density of the various fiber types. We therefore used this muscle to determine potential morphological and biochemical changes triggered by the absence of SCD1. The number of fibers per muscle section was higher in SCD1 knockout mice than in wild-type mice (Figure 3B). Accordingly, the distribution of fiber calibers showed an increase in the amount of fibers of small caliber in SCD1 knockout mice (Figure 3C). We extended these findings by performing SDH histochemistry, and found that the average cross-sectional area of both SDH-positive and SDH-negative fibers was smaller in SCD1 knockout mice than in wild-type mice (Figure 3D). These differences were associated in SCD1 knockout mice with a significant predominance of SDH-positive fibers, which are characterized by a higher metabolic oxidative capacity (Figure 3E).\n10.1371/journal.pone.0064525.g003 Figure 3 Metabolic phenotype of muscle from SCD1 knockout mice.\n(A) Expression of PGC1-α, PPARα and PDK4 in gastrocnemius and tibialis anterior from SCD1 knockout mice (brown columns) and wild-type littermates (white columns). *P\u003c0.05, **P\u003c0.01 (Unpaired t-test, n = 3–11). (B) Number of muscle fibers in tibialis anterior from SCD1 knockout mice (KO, brown column) and wild-type littermates (WT, white column). *P\u003c0.05 (Unpaired t-test, n = 7–10). (C) Distribution of the calibers of muscle fibers in tibialis anterior from SCD1 knockout mice (327 fibers, black circles) and wild-type littermates (283 fibers, white circles). Representative microphotographs of wild-type and knockout tibialis anterior are shown. (D) Averaged cross-sectional area of SDH-positive and SDH-negative fibers in tibialis anterior from SCD1 knockout mice (brown columns) and wild-type littermates (white columns). *P\u003c0.05, **P\u003c0.01 (Unpaired t-test, n = 7–10). (E) Number of SDH-positive (orange bars) and SDH-negative fibers (white bars) in tibialis anterior from SCD1 knockout mice (KO) and wild-type littermates (WT). ***P\u003c0.001 (Chi-square test, n = 283–327). Evaluation of muscle function using the grip strength test revealed no changes in the force developed by hind limbs between SCD1 knockout mice and their wild-type littermates (0.37±0.024 N in SCD1 knockout mice versus 0.37±0.021 N in wild-type mice, n = 7). Along with this, no abnormal spontaneous electrical activity, which would have reflected the typical response of muscle to loss of innervation, was found in the gastrocnemius of SCD1 knockout mice (data not shown). In contrast, we also measured the expression of a series of genes specific to the motor end plate, including the acetylcholine receptor subunits α, γ and ε (AChR-α, AChR-γ and AChR-ε, respectively), and muscle-specific receptor tyrosine kinase (MuSK). Except for AChR-γ, of which an increase would have been considered a sign of muscle denervation [23], the expression of these genes was significantly increased in the gastrocnemius of SCD1 knockout mice as compared to their wild-type littermates, although the changes were less pronounced in the tibialis anterior (Figure 4). In all, these results indicate that the genetic ablation of SCD1 is not detrimental per se to muscle function but promotes a metabolic shift toward a more oxidative capacity, and stimulates the neuromuscular junction gene expression program.\n10.1371/journal.pone.0064525.g004 Figure 4 Gene expression specific to the motor end plate in SCD1 knockout mice.\nExpression of AChR-α, AChR-γ, AChR-ε and MuSK in gastrocnemius and tibialis anterior from SCD1 knockout mice (brown columns) and wild-type littermates (white columns). *P\u003c0.05, ***P\u003c0.001 (Unpaired t-test, n = 4–11).\n\nS","divisions":[{"label":"Title","span":{"begin":0,"end":111}},{"label":"Figure caption","span":{"begin":1828,"end":3006}},{"label":"Title","span":{"begin":1872,"end":1926}},{"label":"Figure caption","span":{"begin":4300,"end":4633}},{"label":"Title","span":{"begin":4344,"end":4414}}],"tracks":[{"project":"2_test","denotations":[{"id":"23785402-21841792-91676678","span":{"begin":576,"end":578},"obj":"21841792"},{"id":"23785402-2027048-91676679","span":{"begin":3829,"end":3831},"obj":"2027048"}],"attributes":[{"subj":"23785402-21841792-91676678","pred":"source","obj":"2_test"},{"subj":"23785402-2027048-91676679","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"2_test","color":"#ec93a3","default":true}]}]}}