PCD is a rare genetic disease characterized by recurrent respiratory tract infections, bronchiectasis, and infertility . SI is often associated with PCD . The first internationally randomized controlled trial in PCD was recently conducted showing azithromycin is effective in reducing exacerbations . Although some cases of SI have been reported , the causes of SI remain unclear and the molecular studies of SI are even more sparse. With the rapid advancement of bioinformatics tools, e.g., the WGCNA, we intended to identify the molecules involved in the formation of SI.
We first identified the DEGs involved in PCD by classical analytical methods. Then, these DEGs were annotated and enriched in a group of GO terms and KEGG metabolic pathways, respectively. Studies have shown that many of these enriched pathways are involved in PCD [31–33]. Furthermore, our results of GSEA revealed that the gene set KEGG_MATURITY_ONSET_DIABETES_OF_THE_YOUNG showed significant difference, suggesting that PCD might be related to the maturity onset diabetes of the young. These results were consistent with those reported previously, showing that both disorders of SI and PCD occur more frequently in children [34, 35]. Because PCD is related to respiratory infections , and the quality of immune function is related to the severity of PCD . Our results of immune cells showed that there were significant differences in the amount of activated contents of dendritic cells in PCD, and the correlation analysis revealed either positive or negative effects of these immune cells, which was important information for the assessment of the immune functions of PCD . Studies on SI have shown that the Bi-allelic mutations in PKD1L1 are associated with the laterality defects in humans , while the DNAI1 gene defects are associated with PCD and situs solitus . Furthermore, two out of the thirteen novel variants, i.e., (1) c.11839 + 1G > A indynein, axonemal, heavy chain 11 (DNAH11) and (2) p.Lys92Trpfs in dynein, axonemal, intermediate chain 1 (DNAI1), were associated with dextrocardia with SI, while one variant, i.e., p.Gly21Val in coiled-coil domain-containing protein 40 (CCDC40), was involved in the absence of the inner dynein arm. Moreover, the homozygous C1orf127:p.Arg113Ter (rs558323413) was also associated with the laterality defects in two related patients . In addition, it has been reported that CCDC11 is associated with laterality disorder , while a homozygous NME7 mutation was associated with Situs Inversus Totalis . Although the discovery of these genes partly explains the occurrence of SI, the genes involved in the formation of SI still need to be further explored.
The molecular modules most closely related to SI were identified based on the WGCNA. The functional analysis of these molecules revealed a group of GO terms and KEGG pathways related to situs inversus. Studies have shown that imbalanced mitochondrial function provokes heterotaxy (i.e., the incorrect placement of visceral organs) via aberrant ciliogenesis, while faulty cilia also prevent the development of proper left-right asymmetry to cause heterotaxy . Furthermore, studies have reported that aberrant left-right patterning in the developing human embryo can lead to a broad spectrum of congenital malformations . About 50% of the SI cases are possibly caused by an inability of embryonic cilia to shift the heart to the left side. Based on the observation of electron microscopy, the missing ciliary components can be visualized directly to determine the heterogeneous nature of this disease based on the molecular basis of this congenital defect . To date, our study is the first report with the identification of these KEGG pathways involved in situs inversus, providing a new direction for the study of the causes of SI. Furthermore, a group of 6 core genes (i.e., ATP5A1, NDUFV2, FOXRED1, NDUFS3, ATP5I, and NDUFB10) closely related to SI were identified based on Cytoscape, indicating that these genes might be the potential targets for the treatment of SI.
Gene regulatory network plays an important role in the pathophysiological process of SI. Our results provide novel insights into the understanding of the pathogenesis of SI and provide potentially novel treatment strategies for this medical disorder. It is noted that our study contains the following limitations: (1) only the top 10 hub genes were comprehensively investigated; (2) it is challenging to verify our conclusions in this study due to the difficulty in obtaining specimens of SI; (3) the functions of hub genes identified in the network constructed in this study need to be further verified.