Succinate induces skeletal muscle fiber remodeling via SUNCR1 signaling
Authors: Ye-Xian Yuan
Zheng-Rui Liao
Tao Wang
Bai-Chuan Deng
Zhi-Hui He
Li-Na Wang
Lv Luo
Can-Jun Zhu
Dong Yue
Qing-Yan Jiang
Ping Gao
Fan Li
Yu-Ping Zhou
Lu-Lu Yu
Pei-Pei Xie
Xing-Cai Cai
Gan Zhou
Yong-Liang Zhang
Ping-Wen Xu
Sarah Schaul
Jin-Ping Yang
Xiao-Tong Zhu
Bing-Qing Liang
Jing-Ren Xu
Man Du
Cong Yin
Cha Zhang
Song-Bo Wang
Qian-Yun Xi
Lin Zhang
Gang Shu
Ya-Qiong Xu
Journal: EMBO reports (2019)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: SUNCR1; aerobic exercise; fiber type; skeletal muscle; succinate.
Affiliations: Guangdong Province Key Laboratory of Animal Nutritional Regulation, College of Animal Science, South China Agricultural University, Guangzhou, Guangdong, China., Division of Endocrinology, Department of Medicine, The University of Illinois at Chicago, Chicago, IL, USA., National Engineering Research Center for Breeding Swine Industry, College of Animal Science, South China Agricultural University, Guangzhou, Guangdong, China.

Abstract:  The conversion of skeletal muscle fiber from fast twitch to slow-twitch is important for sustained and tonic contractile events, maintenance of energy homeostasis, and the alleviation of fatigue. Skeletal muscle remodeling is effectively induced by endurance or aerobic exercise, which also generates several tricarboxylic acid (TCA) cycle intermediates, including succinate. However, whether succinate regulates muscle fiber-type transitions remains unclear. Here, we found that dietary succinate supplementation increased endurance exercise ability, myosin heavy chain I expression, aerobic enzyme activity, oxygen consumption, and mitochondrial biogenesis in mouse skeletal muscle. By contrast, succinate decreased lactate dehydrogenase activity, lactate production, and myosin heavy chain IIb expression. Further, by using pharmacological or genetic loss-of-function models generated by phospholipase Cβ antagonists, SUNCR1 global knockout, or SUNCR1 gastrocnemius-specific knockdown, we found that the effects of succinate on skeletal muscle fiber-type remodeling are mediated by SUNCR1 and its downstream calcium/NFAT signaling pathway. In summary, our results demonstrate succinate induces transition of skeletal muscle fiber via SUNCR1 signaling pathway. These findings suggest the potential beneficial use of succinate-based compounds in both athletic and sedentary populations. 

Retracted: No

PubPeer comments:
 ![file] ![file] ![file] A correction was already issued for this, due to a mis-spelling of SUCNR1 in the title abstract. Given that the paper also appears to contain numerous instances of duplicated images and western blots, it might be a good idea to just go ahead and retract the whole thing. The duplications have been resized and or rotated, and some features removed between images, which makes it highly unlikely this arose as a result of  accidental pasting in the wrong image, as is frequently claimed in such matters. , 
 Thanks for your academic supervision and rigorous attitude to our paper. I understand some of the points, such as tubulin WB in Fig3B 4I and MYCH I IIb of SUC group in Fig7M 3C, due to same samples or same group. For FigEV1M and MYCH I IIb of KO KO+SUC group in Fig7M 3C, we will re-check all our original pictures to response ASAP. , 
 #2 With respect, Dr. Shu, it is difficult to understand how the rotation of an image can occur by chance, or how the change in dimensions of an image can be attributed to an error. These type of errors appear more deliberate than accidental to me, a neutral third-party. No matter how skilled the person preparing the figure was, or how unorganized the record keeping system is (both explanations we often hear), in your reply, I would be interested in hearing exactly *how* these errors occurred. , 
 The journal is aware of these allegations. We would like to point out that the reuse of tubulin is already described in the legend for Figure 4I.  Immunoblots and quantification of pu2010AMPK, PGCu20101u03b1, and myoglobin in gastrocnemius. The same lysates were used for the detection of PGC1u03b1 (100 kDa, Fig 4I), myoglobin (17 kDa, Fig 4I), myosin heavy chain (180 kDa, Fig 3B), and tubulin (48 kDa, shared in both Figs 3B and 4I). , 
 #3 Dear Actinopolyspora Biskrensis, Thanks for your questioning and criticizing. At first glance, I was also shocked by the repeated use of images, and the obvious repetition of adjacent images in such a clumsy way. However, in skeletal muscle study, we cut the slice one by one, each of adjacent slices are almost like twins. So, when you compare this  same picture carefully, there are really different pictures which should be easily distinguished by specific software. I m not trying to find excuses for the responsibility for improper use of pictures. Actually, we repeated the immunostaining and tried to get more clear representative pictures with new microscope at other lab, when we already got the statistical analysis data. Now, we are trying to get the original picures for both statistical analysis and representative one. Thanks for your patient and we are also appreciate for the explanation from EMBO R. , 
 Thanks to EMBO for the comment regarding the western blot, that seems like a reasonable explanation. To the authors, regarding your assertion that the images appear similar due to the use of serial sectioning, this might be OK for when the conditions are the same, but of course you will take note that many of the duplicated images are between DIFFERENT experimental conditions. - In Figure EV1, two different conditions (control and 0.5% succinate) have portions of the same image. - In Fig 7M, two conditions have the same image (SUCNR1KO and SUCNR1KO+SUC). - In Figure 3C, two images in the same  SUC condition from Figure 7M have been reused to represent two different conditions... the 0.5% SUC (pink box) upper image and the 1% SUC (green box) lower image. How can one condition (SUC) in one figure now represent two different conditions in another Figure? TL DR this cannot be explained away by serial sectioning. The resizing and rotation of the images is also of concern. , 
 The duplication between 3B and 4I is noted in the figure legend for 4I:  Immunoblots and quantification of pu2010AMPK, PGCu20101u03b1, and myoglobin in gastrocnemius. The same lysates were used for the detection of PGC1u03b1 (100 kDa, Fig 4I), myoglobin (17 kDa, Fig 4I), myosin heavy chain (180 kDa, Fig 3B), and tubulin (48 kDa, shared in both Figs 3B and 4I). , 
 #6 Dear Paul S Brookes, we have got all the statistic original pictures and found the reason for this unforgivable mistake. I will arrange them in one Word file with detail file information (date) and attach it ASAP. , 
 #8 Dear Gang, we would very much appreciate for you to contact the journal so that we can review your source data and formally correct the scientific record. It s great that you re willing to share on PubPeer, but the platform does not replace the journal when it comes to correcting your paper. , 
 #6 Dear Paul S Brookes, would you please send your email and we will send the screen shot of our original pictures. The Word file is not supported by this reply. , 
 #9 Thanks for your kind remind. I just send the email to *contact@emboreports.org* and try to explain the reason for this mistake with the Word files containing the screen shot of all original pictures needed. , 
 Partial Withdrawal: 7 June 2021  The authors and journal were simultaneously informed of potential image duplications in the original paper in July 2020. The authors found an image processing error that affected Figures 3, 7, and EV1, which resulted in consecutive slices from the same sample being mislabeled and misrepresented as data deriving from different mice of different treatment groups and genotypes. The authors state that this happened during the repeat and staining process and in the preparation of representative images. The authors voluntarily conducted repeat experiments to confirm the conclusions of the affected figures. (figures available at journal site) The journal determined that the conclusions derived from the affected figures were supported by independent experimental results within the paper and recommended an evaluation by an independent institutional investigation. In December 2020, an institutional committee compared the data from the original paper with the repeated experimentation. The committee found that the figures and statistics reported in the original paper were consistent with the repeated experimental data: In Figure EV1E-F, the original data showed a dosage-dependent effect of dietary succinate on MyHC-I levels, which is not fully supported by the repeat data. The repeat data conclude that while there is a significant increase in MyHC-I percentage in response to 0.5% dietary succinate compared with the control, it is not dependent on the dosage. The authors withdraw the phrase u201cdose-dependentlyu201d in the following sentence: u201cConsistently, we found that succinate dose-dependently increased MyHC-I but not MyHC-IIb protein expression in soleus, suggesting an increased proportion of slow-twitch fiber (Figs EV1E-F)u201d. The journal agrees with the authorsu2019 decision to withdraw Figures 3C-D, 7M-N, and EV1E-N and to publish the repeat data with this partial withdrawal notice. All authors agree with this partial withdrawal and apologize for the inconvenience their mistake caused. ,