## 3 Discussion
The significantly elevated levels of SAMM50 mRNA and protein in the established beige adipocytes (Figure 2D,E) were corresponding to its function analyzed by the lentiviral system (Figure 3). Either the suppression or overexpression of SAMM50 was correlated with the expression profile of thermogenic factors, including UCP1 and PPARGC1A (Figures 5 and 6), indicating that SAMM50 regulates the thermogenesis of differentiated beige adipocytes from hADSCs. SAMM50 is essential for mitochondrial membrane organization and respiratory complex assembly and regulates the cristae stability through an interaction with the mitochondrial contact site and the cristae organizing system complex [25; 26]. According to a recent study, SAMM50 can bind to the PINK1 and mitochondrial dynamic factors, including MFN1, MFN2, and MFF and, SAMM50 deficiency causes PINK1-Parkin-mediated activity [28]. This report indicates that SAMM50 plays an important role in mitochondrial dynamics and quality control and that SAMM50 inhibits PINK1-Parkin-mediated mitophagy. Additionally, it has been reported that PINK1-Parkin-mediated mitophagy is highly associated with mitochondrial dynamics [35]. Mitophagy is facilitated through either the increased fission or decreased fusion of mitochondria, whereas it is inhibited by an increased fusion or decreased fission [36]. In this study, the expression levels of the mitochondrial fusion genes, including _MFN1_, _MFN2_, and _OPA1_, were decreased in SAMM50 knockdown, however, no change was observed in SAMM50 overexpression (Figure 4A). Furthermore, the expression levels of the mitochondrial fission genes, including _DRP1_, _DNM2_, and _MFF_, were promoted in SAMM50 knockdown, while they were suppressed in SAMM50 overexpression (Figure 4B). In the knockdown of SAMM50, the mitophagy was promoted by a decreased fusion and increased fission, which is consistent with previous studies. However, in the overexpression of SAMM50, the fusion remained unchanged, but the fission was strongly suppressed, exhibiting results opposite to the previous study with HeLa cells [36]. These results are assumed to be characteristic of beige adipocytes having unique functions and morphology with different mitochondrial populations [37]. The results obtained in this study indicate that the expression of SAMM50 regulates the balance of mitochondrial fusion/fission. In addition, the expression levels of mitochondrial-related genes, including _CYCS_, _COX7A1_, _CPT1B_, and _CPT2_, were all inhibited by the inhibition of SAMM50, whereas it was all elevated in the overexpression of SAMM50 (Figure 4D,E). To confirm this role, the MitoTracker staining revealed that the mitochondrial content fluctuated when the expression of the SAMM50 changed, with the mtDNA copy number showing a consistent trend (Figure 4F,G). It was postulated that the number of mitochondria decreased as mitochondrial degradation was promoted through the inhibition of the fusion gene and the promotion of the fission gene in SAMM50 knockdown. These results are thought to increase mitochondrial biogenesis by inhibiting mitophagy as SAMM50 regulates fusion/fission. As a result, in the thermogenesis of beige adipocytes, the expression of SAMM50 was positively correlated with the expression profile of thermogenic factors, including UCP1 and PPARGC1A (Figures 5 and 6), indicating that SAMM50 could regulate the thermogenesis of differentiated beige adipocytes from hADSCs. Thus, these findings demonstrate that, along with the mitochondrial-related genes, thermogenic genes are also regulated in accordance with the mitochondrial content that is regulated through the expression of SAMM50. Especially, SAMM50, in these roles, may be involved in improving obesity. The thermogenesis of beige adipocytes induces energy consumption with a higher degree of thermogenic plasticity, thus contributing to the treatment of energy-accumulation-induced obesity [7].