Identification and assessment of differentially expressed necroptosis long non-coding RNAs associated with periodontitis in human.BACKGROUND
 Periodontitis is the most common oral disease and is closely related to immune infiltration in the periodontal microenvironment and its poor prognosis is related to the complex immune response.  The progression of periodontitis is closely related to necroptosis, but there is still no systematic study of long non-coding RNA (lncRNA) associated with necroptosis for diagnosis and treatment of periodontitis.


 MATERIAL AND METHODS
 Transcriptome data and clinical data of periodontitis and healthy populations were obtained from the Gene Expression Omnibus (GEO) database, and necroptosis-related genes were obtained from previously published literature.  FactoMineR package in R was used to perform principal component analysis (PCA) for obtaining the necroptosis-related lncRNAs.  The core necroptosis-related lncRNAs were screened by the Linear Models for Microarray Data (limma) package in R, PCA principal component analysis and lasso algorithm.  These lncRNAs were then used to construct a classifier for periodontitis with logistic regression.  The receiver operating characteristic (ROC) curve was used to evaluate the sensitivity and specificity of the model.  The CIBERSORT method and ssGSEA algorithm were used to estimate the immune infiltration and immune pathway activation of periodontitis.  Spearman's correlation analysis was used to further verify the correlation between core genes and periodontitis immune microenvironment.  The expression level of core genes in human periodontal ligament cells (hPDLCs) was detected by RT-qPCR.


 RESULTS
 A total of 10 core necroptosis-related lncRNAs (10-lncRNAs) were identified, including EPB41L4A-AS1, FAM30A, LINC01004, MALAT1, MIAT, OSER1-DT, PCOLCE-AS1, RNF144A-AS1, CARMN, and LINC00582.  The classifier for periodontitis was successfully constructed.  The Area Under the Curve (AUC) was 0.952, which suggested that the model had good predictive performance.  The correlation analysis of 10-lncRNAs and periodontitis immune microenvironment showed that 10-lncRNAs had an impact on the immune infiltration of periodontitis.  Notably, the RT-qPCR results showed that the expression level of the 10-lncRNAs obtained was consistent with the chip analysis results.


 The 10-lncRNAs identified from the GEO dataset had a significant impact on the immune infiltration of periodontitis and the classifier based on 10-lncRNAs had good detection efficiency for periodontitis, which provided a new target for diagnosis and treatment of periodontitis.
R
FactoMineR package in R was used to perform principal component analysis (PCA) for obtaining the necroptosis-related lncRNAs. 
FactoMineR package
The CIBERSORT method and ssGSEA algorithm were used to estimate the immune infiltration and immune pathway activation of periodontitis. 
CIBERSORT method
The CIBERSORT method and ssGSEA algorithm were used to estimate the immune infiltration and immune pathway activation of periodontitis. 
ssGSEA algorithm