Small RNA- and DNA-based gene therapy for the treatment of liver cirrhosis, where we are?

Table 1 Advantages and disadvantages of small RNA and DNA based gene therapy

Strategy	Mechanisms of action	Advantages	Disadvantages
Antisense ODN	RNA-antisense ODN heteroduplex activates RNase H that can degrade the duplexesAntisense ODN physically block the ribosome translocation sterically by hybridization	Antisense ODN can be introduced directly into cellAvailability of chemical modification of antisense ODN	Stability in cells (endonucleolytic and exonucleolytic degradation)Modified antisense ODN stimulates the immune systemDesign and synthesis is more complicated compared with other strategies
siRNA	siRNA incorporated into RISC, which leads to the rapid degradation of the entire mRNA molecule	Great specificity and efficacy: thermodynamic end stability, target mRNA accessibility	Non-specific gene silencing
			Activation of immune response
			RNA degradation by endonuclease
			Expensive for larger experiments
miRNA	Small, non-protein coding RNAs that guide the post-transcriptional repression of mRNA binding at 3’ UTR region	miRNA ability to regulate multiple genesCost effective for long-term experiments	Need for cloning and verification of insert
			Activation of immune response
			RNA degradation by endonuclease
Decoy ODN	Double stranded oligonucleotide containing an enhancer cis-element	Specifically inhibits transcription factor function	Transfection efficiency and delivery to cells
	Target transcription factor binds to decoy ODN and block the interaction of target gene transcription	Allows for the regulation of endogenous and pathological gene expression	DNA degradation by endonuclease

RISC: RNA-induced silencing complex; siRNA: Small interfering RNA; miRNA: Micro RNA; RNase H: Ribonuclease H; 3’UTR: 3’-untranslated region; ODN: Oligodeoxynucleotides.

Table 2 Summary of studies using small RNA and DNA based therapies in liver cirrhosis

Strategy	Target gene	Biological effects	Ref.
Antisense ODN	TGF-β1	Inhibition of liver fibrogenesis in vivo (bile duct ligation) and in vitro (activated HSCs)	[50]
	TβRI and TβRII	Exogenous antisense TβRI and TβRII block in pig serum induced liver fibrosis	[51]
	TIMP-1	Preventive effect on immune induced liver fibrosis progression	[54]
	TIMP-2 (seq1 and seq2)	Hydrodynamic injection of TIMP-2 antisense prevented the progression of liver fibrosis	[55]
siRNA	TGF-β1	TGF-β1 shRNA effectively inhibited CCl4-induced liver fibrosis	[62]
	TGF-β1	Inhibition of the expression of TGF-β1 and inflammatory cytokine in HSC-T6	[63]
	Collagen specific chaperon (gp46)	Effectively resolved the hepatic collagen deposition and prolonged survival in DMN-induced liver fibrosis	[64]
	PDGF receptor beta small subunit (GFAP promoter)	HSCs-specific PDGFR-beta shRNA attenuates CCl4-induced acute liver injury and bile duct ligation-induced chronic liver fibrosis	[65]
	Ubc 13	Galactosylated liposome/siRNA complex effectively exhibited the hepatocyte selective gene silencing	[79]
miRNA	miR-27a and 27b	Down regulation of miR-27a and 27b changed from activated HSC to quiescent HSC	[82]
	miR-29b	Negative regulator for the type I collagen and Sp1 in HSC	[83]
	miR-29 family	Modulation of TGF-β1 and NF-κB signaling pathway in CCl4-induced liver fibrosis	[84]
	miR-199a, miR-199a*, miR200a and miR-200b	Highly expressed miRNAs by miRNA microarray analysis in CCl4-induced liver fibrosis	[85]
Decoy ODN	NF-κB	Inhibition of inflammatory changes and fibrosis during CCl4-induced liver fibrosis	[96]
	Sp1	Inhibition of proliferation and fibrotic gene synthesis in activated HSCs	[99]
	Sp1	Inhibition of TGF-β1 and matrix gene expression in CCl4-induced liver fibrosis	[100]
	NF-κB and Sp1	Inhibition of fibrogenic and proinflammatory response in CCl4-induced liver fibrosis	[104]

ODN: Oligodeoxynucleotide; HSC: Hepatic stellate cell; TβR: TGF-β1 receptor; TIMP: Tissue inhibitor of metalloproteinase; DMN: Dimethylnitrosamine; GFAP: Glial fibrillary acidic protein; CCl₄: Carbon tetrachloride.