Fig 2: LIN up regulated the expression of myogenesis related factors in GA muscle and down regulated the expression of muscle degradation related factors (A) The mRNA expression of Myh2, 4, 7, Trim63, Fbxo32, Igf1 in the GA muscle was assessed by qRT-PCR, 18S was used as an internal control. (B) Protein expression of MyHC, MuRF1, Atrogin1 was evaluated by western blotting, Tubulin was used as an internal control. (C) The relative expression levels of the proteins were quantified using ImageJ software and normalized to Tubulin and corrected to Group NC. Data shown as mean ± S.E.M. (n = 3); *p < 0.05, **p < 0.01, ***p < 0.001 vs. Group LLC + DDP, #p < 0.05 vs. Group LLC + DDP + LIN(L).

Fig 3: High glucose induces SUMOylation of MuRF1. (A) WB of empty vector transfected C2C12 cells (mock) or cells after transfection with GFP, GFP-MuRF1, and GFP-MuRF1-K238R plasmids cultured in normal (N) and high glucose (H) medium for 6 h. Cell lysates were fractionated by SDS-PAGE and membranes probed with anti-SUMO2 antibodies to determine the conjugation level of SUMOylated protein. SUMOylated proteins decreased in cells cultured in high glucose medium and transfected with GFP-MuRF1-K238R. Anti-GFP antibodies were used to identify the GFP and GFP-MuRF1 protein levels and anti-GAPDH antibodies were used as protein loading control. (B) Quantification of SUMO2 conjugates from three independent experiments and normalized with the loading control GAPDH. ***P < 0.001, **P < 0.01. (C) Membranes in a were also probed with anti-PIAS4 and anti-UBC9 antibodies to detect the endogenous level of two SUMO-conjugating enzymes. (D) Quantification of three independent experiments normalized with the correspondent GAPDH signal as loading control. PIAS4 and UBC9 protein levels increased in cells cultured in high glucose medium. Gray bars indicate normal glucose (5.5 mM) and red bars indicate high glucose (25 mM). (E) Cellular ROS detection in C2C12 cells transfected with mock, GFP, GFP-MuRF1, and GFP-MuRF1-K238R plasmids and incubated for 6 h with fresh normal glucose (N) and high glucose (H) medium. ROS measurement was determined with fluorescence intensity as the ratio between excitation and emission values from 485/535 nm wavelength. The experiment was performed in triplicated from of three independent transfection experiments. The fluorescence detected in the non-transfected cells was removed from all the values. Cellular ROS activity was reduced in C2C12 cells transfected with GFP-MuRF1 and incubated in high glucose for 6 h before the assay. ***P < 0.001.

Fig 4: BiP expression correlated with myofiber atrophy. (A) BiP staining of muscle from a patient with IMNM, a patient with DM, and, a patient with ASS showing abnormal positivity in these cells (*). These cells were positive for muscle RING finger protein-1 (MuRF1). Magnification: ×200. (B) Double IF staining demonstrating the staining of BiP and MuRF1 in the same myofibers in a section from a patient with IMNM. Scale bar, 50 µm. (C) Associations between the percentage of positive BiP and sarcoplasmic MuRF1 expression in muscle tissue obtained from patients with IMNM, DM, and ASS. (D) Relationships between the expression levels of BiP and sarcoplasmic muscle atrophy F-box (MAFbx) expression levels in patients with IMNM, DM, and ASS biopsied muscle. (E) Correlations between the expression levels of BiP and variability coefficient in IMNM, DM, and ASS skeletal muscle sections.

Fig 5: LIN activated Akt/FoxO pathway in GA muscle (A) Protein expression of MyHC, MuRF1, Atrogin1 was evaluated by western blotting, Tubulin was used as an internal control. (B) The relative expression levels of the proteins were quantified using ImageJ software and normalized to Tubulin and corrected to Group NC. Data shown as mean ± S.E.M. (n = 3); *p < 0.05, **p < 0.01 vs. Group LLC + DDP, #p < 0.05 vs. Group LLC + DDP + LIN(L).