Increasing evidence has shown that ferroptosis, a recently discovered PCD, plays a crucial role in progression of MS. However, profiling of it regulars across MS has yet to be clarified. In the current study, we systematically investigated FRGs associated with MS on the basis of WGCNA and 3 FRG signatures for MS were firstly constructed. The core genes interacted with each FRG signature were analyzed in PPI. Functional analyses revealed that biological functions related to metabolism, inflammation and immunity, microglia activation, oxidation, and mitochondria were enriched.
Previous studies demonstrated that ferroptotic cell death resulted from fatal lipid peroxidation [22]. In this regard, the accumulation of intracellular iron caused by the depletion of ferritin or iron transporters and subsequent peroxidation are fundamental mechanisms that lead to the accumulation of lipid peroxides and ferroptosis. Among the 3 identified FRG signatures, HMOX1 is a phase II enzyme which is widely recognized to metabolize heme into biliverdin/bilirubin, carbon monoxide, and ferrous iron, and it has been suggested to demonstrate cytoprotective effects or govern ferroptotic progression depends on the degree of ROS production and following oxidative damage in response to stimulatory cues [40]. LPCAT3, a trans-acylase, is one of important factors in ferroptosis. It was reported to participate in the maintenance of sufficient levels of oxidation substrates which is a significant required constituent of the ferroptotic program. On the other hand, LPCAT3 was also crucial in M1/M2-macrophage polarization by promoting M2 polarization [38]. In the previous rare studies, RPL8 encoded a component of the 60S ribosomal subunit presumably regulating mitochondrial fatty-acid metabolism and translation, which might be a specifically required gene for ferroptosis [39]. It was noteworthy that HMOX1 was significantly down-regulated in MS, and LPCAT3, RPL8 were expressed significantly differently from HC but similarly undetermined in MS in the present study. And there might be 3-fold main implications existing in the expressions of these 3 genes. First, the down-regulation of HMOX1 and uncertainty of LPCAT3 and RPL8 in MS approximately adhered to their bright and dark sides in ferroptosis. Second, the mentioned consistency additionally provided robust evidence that ferroptosis played a critical role in the progression of MS. Third, the current study further demonstrated that the ROC curve generated using these 3 FRGs accurately predicted MS with AUC of 0.76, 0.90, and 0.99. The coexistence of HMOX1, LPCAT3 and RPL8 might trigger ferroptosis, highlighting the pivotal roles of these FRGs in MS, and the potential of HMOX1-based, LPCAT3-based and RPL8-baesd MS therapy.
Although the mechanisms underlying MS progression to ferroptosis have been an intense area of research in the past few years, the whole and specific modulation between ferroptosis and MS remains elusive. GO and KEGG analyses of DEGs between MS and HC indicated that the DEGs corresponding to biological functions were closely related to inflammation and immunity such as protein antigen binding, mitochondrial dysfunction such as mitochondrial translation, microglia activation such as toll-like receptor signaling pathway, oxidation such as phosphatase activity, which further verified aforementioned pathogenic mechanisms of MS. Based on 3 identified FRG signatures, we performed GSEA and GSVA analyses and interestingly discovered that the immunity and inflammation-related biological function such as primary immunodeficiency, microglia activation-related biological function such as JAK STAT signaling pathway, oxidation-related biological function such as oxidative phosphorylation pathway, mitochondria-related biological function such as DNA replication pathway were enriched in the high-expression groups of these FRGs, which strongly validated that ferroptosis was indeed closely related to MS and shared common pathways with MS in gene aspects. Remarkablely, this study demonstrated that many metabolism-related biological functions such as glycolysis gluconeogenesis, amino sugar and nucleotide sugar metabolism, pyruvate metabolism, and fatty acid elongation were significantly enriched in high expression of HMOX1, LPCAT3 and RPL8 groups, which gave a novel crosstalk between ferroptosis and MS from the point of metabolism. As the understanding of complex biological processes of ferroptosis increases, it has been revealed that the initiation and execution of ferroptosis is not only closely connected with metal ions dysfunction, but also crosslinks with energy metabolism including amino acid, fatty acid, pyruvate, glutathione, phospholipids, and NADPH [12]. Moreover, the imbalance between energy production and consumption has been observed in demyelination during MS lesions including the activation of aerobic glycolysis, the increase of aerobic glycolysis and lactate production, and the decrease of pyruvate dehydrogenase activity [41]. Based on these valuable enrichment and PPI results of 3 FRG signatures in the present study, one possible speculation is that the role of ferroptosis in myelin breakdown might not only be neurotoxicity concomitant with CNS inflammation, mitochondrial dysfunction, oxidative stress, and microglia activation, but also be a direct and important regulator of metabolism in demyelination in MS. And it is reasonable to assume that HMOX1, LPCAT3 and RPL8, as FRGs, are likely to be correlated with pathogenic mechanisms of metabolism, inflammation and immunity, mitochondrial dysfunction, oxidation, and microglia activation in MS. In addition, the core genes of HMOX1, LPCAT3, and RPL8 during the progress of MS were investigated in PPI, which further provided insights into the potential of FRG-based MS therapies.
There are several limitations of this study. First, 3 FRG signatures were all constructed and validated with retrospective data from GEO. More prospective real-world data are warranted. Second, since current data only provide RNA-level quantifications for FRGs, whereas the ferroptosis process relies on proteins, there could be a variety of inaccuracies. Third, the detailed molecular mechanisms for ferroptosis are still unclear, and currently, the identified FRGs potential have various other functions; thus, the clinical utility of FRG signature might be limited and needs further evaluation.