Analysis of global publications. Variations in the quantity of academic papers on a certain research field is a significant indicator for the development trend. Plotting the quantity of publications over time and conducting multivariate statistical analysis contribute to understanding the research level and future trend. A total of 2999 publications from 2000 to 2019 were derived from WOS database according to the search criteria. Most research was published in the last 10 years (2010–2019, 2,830, 94.36%). An increasing trend of global publications during the last 20 years was found, which shows the relative research of mitochondrial dynamics will be more and more concerned (Fig. 2c). Furthermore, Fig. 2d showed the logistic regression model fitting curves of the number of publications on mitochondrial dynamics research in the future per year. According to publications, the top 20 productive countries were listed in the Fig. 2b. USA (1184,38.542༅) with the most number was the most contributor, followed by China (699༌23.0༅), Germany (235༌7.65༅), Italy (204༌6.641༅) and Canada (182༌5.924༅), the top 25 countries that had made the greatest contributions in mitochondrial dynamics research were shown in Fig. 2a, the darker the color, the more the number of publications. As expected, these productive countries are either economically developed or in a rapid development stage, which attach great importance to scientific research. When it comes to the most contributive institutions, research orientations and funding, the ranking from WOS database were as followed respectively (Fig. 3): The Johns Hopkins University (59༌1.921༅), Chinese Academy of Sciences (53༌1.725༅) and Universitat de Barcelona (50༌1.628༅) and were listed in the top 3, and Cell Biology (930༌30.273༅), Biochemistry Molecular Biology (879༌28.613༅) and Neurosciences Neurology (505༌16.439༅) were listed in the top 3, and NIH (853༌27.767༅), HHS (853༌27.767༅) and NSFC (452༌14.714༅) were listed in the top 3.
Quality of publications of different countries. In regards to WOS database analysis, we tallied the total citations, average citations and H-index of each country (Fig. 4). Papers from USA had the highest number of citations (65,447), followed by Germany (1,1653), China (1,1569). At the same time, Papers from USA had the highest H-index (125). Germany ranked second in H-index (55), followed by China (52), Canada (49) and Italy (49). While the top 5 countries in average citation frequency were Israel (63.54), Switzerland (59.33), USA (55.28), Germany (49.59) and Canada (48.13).
Bibliographic coupling analysis. Bibliographic coupling analysis aims to find the relatedness of items based on the number of references they share and generate the knowledge domain map (KDM) of main research journals, institutions and countries in order to demonstrate the collaboration network among them in mitochondrial dynamics research. In Fig. 5, each sphere represents a journal, an institution and a country, and the sphere size represents the power of total link strength (TLS). The links between sphere represent the associations where the greater width of the link (namely link strength) means the closer correlation, which is also applied to co-authorship analysis, co-citation analysis and co-occurrence analysis. Sixty-six journals were shown in Fig. 5a in accordance with total link strength (TLS) and the size of sphere representing the power of journal in the research field of subchondral bone. The top 5 journals with the greatest total link strength were as follows: Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease (Impact Factor, IF = 4.328, 2018, TLS = 102,519 times), Antioxidants & Redox Signaling (IF = 5.828, 2018, TLS = 79,934 times), PLoS ONE (IF = 2.776, 2018, TLS = 71,751 times), Mitochondrion (IF = 3.449, 2018, TLS = 71,751 times) and Journal of Biological Chemistry (IF = 4.106, 2018, TLS = 60,878 times). There were 151 institutions shown in Fig. 5b based on papers with the minimum number of documents of an organization more than 10. Universitat de Barcelona (TLS = 172,099 times) ranked the first, followed by Case Western Reserve University (TLS = 169,681 times), The Johns Hopkins University (TLS = 142,157 times), Caltech (TLS = 155,568 times) and The University California, San Diego (TLS = 137,743 times). The top 5 countries based on papers with the minimum number of documents of a country more than 5 were shown in Fig. 5c, including USA (TLS = 2,625,487times), China (TLS = 943,403 times), Germany (TLS = 724,311 times), Italy (TLS = 603,911 times) and England (TLS = 550,749 times).
Co-authorship analysis. Co-authorship analysis aims to find the relatedness of items based on their number of co-authored documents and generate the knowledge domain map of main research authors, institutions and countries in order to demonstrate the collaboration network among them in mitochondrial dynamics research. Creating and analyzing the KDM of co-authorship network of productive authors, institutions and countries can provide valuable information for individual researchers to seek cooperation partners, for research organizations to develop cooperation groups, and for countries to achieve the goal of academic exchanges. Authors, institutions and countries were analyzed via VOS viewer and 67 authors, 150 institutions and 45 countries were shown in Fig. 6. Zhu, XW (TLS = 52 times), Wang, XL (TLS = 52 times), Perry, G (TLS = 44 times), Reddy, PH (TLS = 38 times) and Chattipakorn, N (TLS = 38 times) were considered as the top 5 authors with the largest TLS. By the same way, the top 5 institutions with the TLS were as follows: The Johns Hopkins University (TLS = 54 times), McGill University (TLS = 48 times), Centre National de la Recherche Scientifique (TLS = 46 times), Universitat de Barcelona (TLS = 45 times) and Baylor College of Medicine (TLS = 44 times). Both authors and institutions were based on papers with the minimum number of documents of an author or organization more than 10. The top 5 countries with largest TLS based on papers with the minimum number of documents of a country more than 5 were USA (TLS = 614 times), England (TLS = 216 times), Germany (TLS = 210 times), China (TLS = 205 times) and Italy (TLS = 167 times).
Co-citation analysis. Co-citation analysis is purposed to determine the relatedness of items based on the number of times they are cited together. Through co-citation analysis, the important knowledge bases of the research field can be found efficiently and conveniently from the mass of cited references. Furthermore, the relevance of publications can also be analyzed and excavated. Papers with the minimum number of citations of a cited reference more than 50 were analyzed using VOS viewer and 336 references were shown in Fig. 7a. The top 5 were as follows: The Journal of Cell Biology. 2003. 160(2): 189–200.( TLS = 14,056 times), The EMBO Journal. 2008. 27(2): 433 − 46.( TLS = 12,836 times), Molecular biology of the cell. 2001. 12(8): 2245-56.( TLS = 10,612 times), Developmental cell. 2001. 1(4): 515 − 25.( TLS = 10,325 times) and Nature genetics. 2000. 26(2): 207 − 10.( TLS = 9,976 times). Journals with at least 50 citations were analyzed through VOS viewer and there were 480 journals shown in Fig. 7b. The top 5 journals with the largest total link strength were following: The Journal of Biological Chemistry (TLS = 1,102,933 times), Proceedings of The National Academy of Sciences of The United States of America (TLS = 900,746 times), Journal of Cell Biology (TLS = 807,056 times), Cell (TLS = 581,151 times) and Nature (TLS = 557,495 times). Papers with the minimum number of citations of an author more than 50 were identified and analyzed via VOS viewer and 468 authors were shown in Fig. 7c. The top 5 authors with the greatest total link strength were as follows: Chen HC (TLS = 67,672 times), Ishihara N (TLS = 35,069 times), Karbowski M (TLS = 34,765 times), Twig G (TLS = 31,575 times) and Wang, XL (TLS = 24,143 times).
Co-occurrence analysis. Co-occurrence analysis purposes to determine the relatedness of items based on the number of documents in which they occur together. Through the analysis, popular topics and directions were identified, which contribute to monitor and follow up the development of science research and programs[47, 48]. Keywords with the minimum number of occurrences more than 80 in all included publications were analyzed via VOS viewer. As shown in Fig. 8a, 62 identified keywords were classified into the 3 clusters: “Related disease research”, “Mechanism research” and “Cell metabolism research”. The results demonstrated that the most prominent fields of mitochondrial dynamics included the above 3 directions. For the “Related disease research” cluster, the primary keywords were Alpha-Synuclein, Amyloid-Beta, Alzheimer-disease, Parkinsons-disease, mitochondrial dysfunction and oxidative stress. For the cluster of “Mechanism research”, frequently used keywords were Apoptosis, Cytochrome-c, Drp1, OPA1, Dynamin-related protein, Mitofusin 2, Mitochondrial fusion or fission. In the “Cell metabolism research” cluster, the main keywords were Activation, Autophagy, Metabolism, Mutation, Gene-expression and Degradation.
20,279Keywords were color coded by VOS viewer based on the average time they appeared in the total of 2999 publications (Fig. 8b). The blue color means the keywords appeared early and red colored keywords appeared later. Before 2012, most studies focused on “Saccharomyces-cerevisiae”, “Cytochrome-c release” and “Morphology”. The latest trends showed that “Mitofusin 2”, “Dynamin-related protein 1”, “Mitophagy”, “Biogenesis” and “Mechanism” would be concerned more widely in the future.
Papers with the minimum number of occurrences of a keyword more than 80 were identified and analyzed via VOS viewer. Density visualization map (Fig. 8c) was exported by VOS viewer. The times of occurrence of a key word was defined as the color of the area. The larger the tines, the warmer the color is. Blue corresponds with the lowest item density and red corresponds with the highest item density. “Fission”, “Fusion”, “Mitochondria”, “Oxidative stress” and “Apoptosis” were the most relevant keywords related to mitochondrial dynamics in general.