With the aging of the population, the incidence rate of cataract has been increasing year by year. With the rapid development of molecular biological cytology in recent years, the pathogenesis of cataract has been deeply studied at the molecular and genetic levels, but its exact mechanism remains unclear[13]. In recent years, increasing studies have focused on understanding the mechanisms of pyroptosis in various diseases, and identifying the genes and pathways that are implicated in this process. The aim of this study was to unravel genes involved in the pyroptosis related genes of age-related cataract, which was helpful in investigating the pathogenesis of age-related cataract and may provide valuable therapeutic targets for further clinical therapy. In this study, age-related cataract and pyroptosis-related genes were found from the GEO and previous studies, respectively. After analysis, 6156 DEGs genes of age-related cataract and 55 genes related to pyroptosis were obtained, including 7 pyroptosis related gens of age-related cataract.
GSEA analysis results showed that most of the upregulated genes and pathways were involved IL18 signaling pathway, IL2 signaling pathway, IL4 signaling pathway, Noth signaling pathway, MAPK signaling pathway, cytokines and inflammatory response, and also showed that most downregulated genes and pathways were involved FOXM1 signaling pathway, PLK1 signaling pathway.
GO annotation, KEGG and Reactome Pathway enrichment analysis were done by the Metascape online tool, and the upregulated genes were particularly concentrated in regulation of response to lipopolysaccharide(LPS), Cellular response to biotic stimulus, Cellular response to lipopolysaccharide, NOD-like receptor signaling pathway, TNF signaling pathway and Coronavirus disease -COVID-19. LPS could induce activation of p38, suggesting a possible mechanism by which aldose reductase(AR) inhibition reduces inflammation. Pandey et al[14] have hypothesized that blockade of AR helps to reduce the production of ROS and associated oxidative stress, which are important components that drive the pro-inflammatory response following exposure to cells to LPS.
The PPI network was obtained on the basis of analysis applying the STRING online tool and Cytoscape software. IL1β、IL1A、IL6、TNF、PSTPIP2、TNFAIP3、NLRP3 were the uppermost 7 genes in the PPI network, as their connectivity degree was relatively high.
The top 5 hub genes were IL6, TNF, IL1A, IL1β, NLRP3, all of these genes were significantly upregulated. To verify the expression of these genes in age-related cataract, relevant literature was searched and summarized in Table 1[15–18]. These genes need to be further verified by experiments, especially in the age-related cataract.
The original IL6 family cytokines consist of seven cytokines: IL6, LIF, CNTF, CLCF1, OSM, CT-1, and IL11. Soluble IL6Ra (sIL-6Ra) interacts with IL-6, forming the IL-6/sIL-6Ra complex, which subsequently induces IL6 trans-signalling by binding cell membrane expressed gp130[19]. Initiation of IL6 signaling through gp130 is mainly mediated by phosphorylation of JAK family kinases, which are constitutively associated with the cytoplasmic region of gp130. JAK1 elicits phosphorylation and homodimerization of STAT3, and then induces translocation into the nucleus and its transcriptional activity[20]. IL6 trans-signalling is recognized to enhance IL-6 activity under inflammatory conditions and moreover to inhibit intraocular T-cell apoptosis, which likely exacerbates or prolongs the inflammatory and oxidative stress process, which are closely related to age-related cataracts [21].
TNF-α is a kind of pyrogen that could increase the secretion of IL1β by stimulating Macrophages, while IL1β can stimulate other cells to release IL6[22]. IL1β can also cause inflammation and the induction of inflammatory responses, induce IL6 and TNF-α expression, stimulate immune cells and stroma cell to produce IL1β[23], more worse, the property of IL6 is similar to that of IL-1β, thus forming a vicious circle and accelerating the inflammatory response. TNF-α levels in cataract lens that also activates NF-kB signal pathway that is involved in cataractogenesis[24].
IL-1α and IL-1β are synthesized as precursor proteins, which are then proteolytically cleaved. Both IL-1α and IL-1β share IL-1R as their common receptor. It is a key event in the induction of inflammatory and pyroptosis response[25]. As IL-1α is present in the cell in a fully bioactive form, necrotic cell death results in the liberation of full-length IL-1α, which serves as an alarmin such as S100A proteins or HMGB1 are preformed proteins, which are expelled from the cell after disruption of the cell membrane to induce inflammation[26]. IL-1β cannot act as an alarmin as it needs to be processed to be active. Inflammasomes as cytosolic protein complexes responsible for the activation of inflammatory caspases can once being activated then cleave IL-1β and IL-18 and release IL-1α, IL-1β, and also IL-18 as pro-inflammatory mediators of pyroptosis, as not only caspase-1 itself but pro-IL-1β and pro-IL-18 are substrates of caspase-1, activated caspase-1 cleaves these mediators into their biologically active forms, which are then secreted[27].
Inflammasomes structurally consist of a NOD-like receptor (NLR) protein such as NLRP1, NLRP3, or NLRC4 and the adaptor protein ASC, via which caspase-1 is recruited to the complex[28]. NLRP3 plays a vital role in modulating innate immune function. Activation of the NLRP3 inflammasome is dependent on ROS accumulation, which then mediates caspase-1 activation followed by increases in proinflammatory IL-1β expression[29]. Zou et.al[30] proposed an important and interesting viewpoint that NLRP3 may have a functional role during the progression of cataract because of the significant increase of NLRP3 mRNA and protein expressions in H2O2-induced HLEB3 cells in comparison with the control, and the protein level of caspase-1 and IL-1 also increased. All these phenotypic changes may be related to pyroptosis.
Table 1
The expression of related genes level in age-related cataract by literature.
| Express | Type | Sample | Conclusion |
IL6 | Upregulation | Cytokines | Tear | Higher tear levels of IL-6 correlated with age of cataract patients[15] |
TNF-α | Upregulation | Cytokines | Serum | TNF-α levels significantly increased in age-related cataract as compared to normal healthy Individual[16] |
IL1A | Upregulation | Cytokines | Tear | IL1A levels increased in age-related cataract as compared to control, but P>0.05[15] |
IL1β | Upregulation | Cytokines | Serum | The serum levels of IL6, IL1β, CRP and TNF- α in the observation group were higher than tho- se in the control group[17] |
NLRP3 | Upregulation | mRNA | HLECs | The TXNIP/NLRP3 inflammasome pathway promotes HG-induced inflammation and HLEC pyroptosis, which is negatively regulated by SIRT1[18] |
HLEC: Human lens epithelial cells |