Abbreviations: EP, Experimental periodontitis; DM, diabetes mellitus; MS, metabolic syndrome; PE, periodontitis; OVX, ovariectomized; Prob, probiotic ; Met, metformin; 5FU, 5-fluorouracil; PDLSCs, periodontal ligament stem cells; ER stress, endoplasmic reticulum stress; IL-1β, interleukin-1 beta; TNF-α, tumor necrosis factor-alpha; Cx43, connexin 43; L. reuteri, Lactobacillus reuteri; L. casei 01, Lacticaseibacillus casei 01; L. rhamnosus EM1107, Lactobacillus rhamnosus EM1107; HN019, Bifidobacterium animalis subsp. The gene discussed is GJA1; the disease is periodontitis.