Intertwined roles of microRNA-155 and metformin in osteoarthritis: Novel potential diagnostic, prognostic, and therapeutic modulators

Table 1 Transcription factors binding sites in the MIR155HG gene

Number of MIR155HG transcription binding sites
Three (3) sites	Two (2) sites	One (1) site	Oncology-associated
Hypoxia-inducible factor-1 alpha	Nuclear factor kappa-B, forkhead box protein P3 (associated with oncogene special AT-rich binding protein-1), ETS proto-oncogene 1	RNA Polymerase II Subunit A, mothers against decapentaplegic homolog 4, interferon-sensitive response element, interferon regulatory factors, Activator protein 1, CCAAT/enhancer-binding protein alpha), ETS family member ELK3	DNA promoter methylation and transcription factor (SP1), v-myb myeloblastosis viral oncogene homolog, Annexin A2, breast cancer 1, early onset

ETS: Erythroblast transformation-specific.

Table 2 Direct gene targets of microRNA-155 relevant to osteoarthritis

Gene symbol	Full gene name	Action	Ref.
AGTR1	Angiotensin II type 1 receptor gene	AGTR1 gene repression downregulates its translation, thereby lowering AT1R membrane expression and downstream signalling, like endogenous AT1R blockade redirecting Ang II towards its alternative receptor Ang II type 2 receptor	Yang et al[88]
ARG2	Arginase2	ARG2 upregulates MMP-3 and MMP-13 via the NF-κB pathway, causing destruction of OA cartilage; repressing ARG2 impairs oxidative phosphorylation, increases and stabilises HIF-1α and could represent an initial protective mechanism in OA	Dunand-Sauthier et al[80]
ATG3, ATG5, ATG14, FOXO3, GABARAPL1, MAP1 LC3, ULK1, RICTOR	-	Repression of autophagy related genes results in potent suppressor of autophagy in human chondrocytes	D'Adamo et al[47]
BACH1	BTB and CNC homology 1, basic leucine zipper transcription factor 1	Translational repression of BACH1 leads to potent anti-inflammatory, cytoprotective, antioxidant programs through heme oxygenase	Takada et al[92]
Bmal1	Brain and muscle Arnt-like protein 1	MiR-155 induction can repress Bmal1 directly in macrophages, endothelial cells and bone marrow mesenchymal stem cells. Disturbed Bmal1/HIF-1α interactions, a crucial pathway in chondrocyte homeostasis in hypoxia, leads to enhanced MMP-13 levels and catabolic chondrocyte effects. MiR-155-induced disturbance of Bmal1 disrupts endochondral bone formation via melatonin receptor 1/AMPKβ1/Bmal1 signaling axis	Curtis et al[74], Liang et al[75], Lee et al[76], Yu et al[77]
Cab39	Calcium-binding protein 39	Cab39 is a component of the trimeric LKB1-STRAD-Cab39 complex and regulates the activity of LKB1 and thus activates the phosphorylation of AMPK, thus, if repressed by miR-155, would hamper AMPK activation and negatively impact chondrocyte survival	Shi et al[69]
CASP3	Caspase 3	Knee OA synovial fluid increased miR-155-5p-induced inhibition of macrophage apoptosis by targeting CASP3	Li et al[61]
C/EBPβ	CCAAT/enhancer binding protein β	Repression of C/EBPβ and its downstream target genes nuclear factor erythroid 2-related factor 2, SOD1, and hemeoxygenase-1, thereby inducing reactive oxygen species generation. C/EBPβ repression leads to miR-143 repression, thus resulting in upregulation of hexokinase 2 expression. MiR-155 C/EBPβ repression could possibly lead to peroxisome proliferator-activated receptor γ downregulation	Karkeni et al[59], Onodera et al[78], Jiang et al[82]
COX-2	Cyclooxygenase 2	As COX-2 is highly expressed in osteocytes and gives rise to abnormal subchondral bone formation, it is of importance that NF-κB induces miR-155/COX-2 expression in macrophages and that miR-155 can bind COX-2, induce COX-2 reporter activity, and maintain mRNA stability, thereby potentially affecting subchondral bone remodeling	Yuan et al[89], Qiu et al[94]
Ets-1	E26 transformation-specific sequence-1	Ets-1 plays a role in OA inflammation and angiogenesis through its regulation of MMPs	Mahesh and Biswas[14]
GDF6	Growth differentiation factor 6	Activation of Piezo-Type Mechanosensitive Ion Channel Component 1 leads to the upregulation of miR-155-5p which represses the downstream target gene GDF6 and accelerates chondrocyte senescence and cartilage degradation	Qin et al[65]
HIF1A	Hypoxia inducible factor 1A	HIF1A is a direct target of miR-155 and decreases the HIF-1α mRNA. HIF-1α and miR-155 are together in a feedback loop whereby HIF1a induces miR-155 in hypoxia. Functional HIF-1α is required for energy production in chondrocytes though its control of basal glycolytic enzymes, phosphoglycerate kinase, and glucose transporter. The expression of HIF-1α, a crucial regulator in chondrocyte homeostasis in hypoxia, is decreased through Bmail1 disruption leading to enhanced MMP-13 Levels and catabolic chondrocyte effects	Zhang et al[27], Lee et al[76]
IGF1	Insulin growth factor 1	Negative regulation of IGF-1 downregulates IGF-1, a crucial molecule involved in repair of OA cartilage damage	Shen et al[72]
IKBKE	Inhibitor of nuclear factor kappa-B kinase subunit epsilon	MiR-155 targets IKBKE that participates in synovial inflammation, ECM destruction	Montagne et al[66], Long et al[67]
LEPR	Leptin receptor	MiR-155 repression of LEPR via inhibition of AMPK, which ultimately increases osteoclast activation and bone resorption of osteoclasts in alendronate-treated osteoporotic mice	Mao et al[91]
Mafb	Musculoaponeurotic fibrosarcoma oncogene family, protein B	Elevated miR-155 in hyperlipidemia improved glucose metabolism and the adaptation of β-cells to obesity-induced insulin resistance through suppression of Mafb and subsequent IL-6 – induced glucagon-like peptide 1 production in α-cells	Zhu et al[90]
MAPK	Mitogen-activated protein kinase	MiR-155/MAPK pathway signalling regulates chondrocyte activities and ECM degradation	Cazzanelli et al[93]
Mfn1/2	Mitofusin 1	Elevated miR-155 in OA can induce cellular senescence by regulating mitochondrial dynamics by promoting fusion through an increase in the expression of Mfn2	Wen et al[73]
PIK3R1	p85α regulatory subunit of PI3K	MiR-155 promotes chondrocyte apoptosis and catabolic activity through targeting PIK3R1-mediated PI3K/Akt pathway activation. Repressions modulate glycolysis via the PIK3R1-PDK/Akt-FOXO3a-cMYC axis	Kim et al[81]
PRKA	AMPK gene	MiR-155 targets 3’ UTR of AMPK mRNA, downregulating it. AMPK negatively controls mammalian target of rapamycin, the main negative regulator of autophagy, thereby suppressing autophagy and negatively impacting chondrocyte survival	Zhang et al[68]
Runx2	Runt-related transcription factor 2	As a direct target of miR-155, Runx2 repression in articular chondrocytes would be expected to slow OA progression. MiR-155 can regulate the RANKL expression via Runx2 mediated transcriptional inactivation; RANKL/RANK are key players in the bone remodeling process and subchondral bone remodeling	Wang et al[2], Komori[87]
RANKL	Receptor activator of nuclear factor kappa-B ligand
SHIP1	Src homology 2-containing inositol phosphatase-1	SHIP-1 repression in clinical and experimental arthritis increases the production of proinflammatory cytokines	Kurowska-Stolarska et al[42]
SIRT1	Sirtuin 1	MiR-155 directly targets and represses SIRT1, thereby indirectly downregulating and preventing AMPK activation and negatively impacting chondrocyte survival. SIRT1-downregulation activates the NLRP3 inflammasome	Hong et al[70], Lu et al[86]
Smad2/5	Mothers against decapentaplegic homolog 2/5	Elevated miR-155 in OA effectively increases Smad2 and reduces Smad5 transcription tipping the balance in the TGF-β1 (Smad2)/bone morphogenetic protein 2 (Smad5) signalling towards TGF-β1 and anabolism in an effort to counteract OA progression. MiR-155 induced Smad2 repression induces pyroptosis in knee OA via activation of the NLRP3/caspase-1 pathway	Gu et al[83], Chen et al[84], Shao et al[85]
SOCS1	Suppressor of cytokine signaling 1	Repression and decreased expression of SOCS1 contributes to the increased production of TNF-α, IL-1β and enhanced M1 macrophage polarization and apoptosis inhibition in OA	Li et al[61], Zhang et al[71]
SOD1/2	Superoxide dismutase 1/2	Binds and represses SOD1 3'UTR as well as diminishes SOD2 expression through FOXO3a repression	Bi et al[79]
TNF	Tumour necrosis factor	The miR-155 promoter was activated by TNF-α and at least partly through NF-κB leading to a direct, positive correlation between miR-155 expression and mRNA levels coding for TNF-α. Elevated miR-155 induces inflammatory response, chemokine expression, and macrophage migration, strongly participating in the establishment of a proinflammatory status which at least in part happens through PPARG downregulation	Karkeni et al[59]
PPARG	PPARγ

Ang II: Angiotensin II; Akt: Protein kinase B; AMPK: Adenosine monophosphate-activated protein kinase; AT1R: Angiotensin II type 1; Cab39: Calcium-binding protein 39; ECM: Extracellular matrix; HIF-1α: Hypoxia-inducible factor 1 alpha; IL: Interleukin; LKB1: Liver kinase B1; MiR-155: MicroRNA-155; MMP: Metalloproteinase; mRNA: Messenger RNA; NF-κB: Nuclear factor kappa-B; NLRP3: NOD-like receptor family pyrin domain-containing 3; OA: Osteoarthritis; PI3K: Phosphoinositide 3-kinase; TGF-β1: Transforming growth factor β1; TNF-α: Tumour necrosis factor-alpha.