Table 2.

Different nucleic acid structures used for naked gene therapy

Type of nucleic acid	Detail	Previous success in kidney gene therapy
miRs and antagomirs	•miRs are small non-coding RNAs with a length of 18–25 nucleotides which bind to the 3′ UTR of the target gene mRNA and posttranscriptionally regulate the gene expression44 •antagomirs specifically silence endogenous miRNAs45	•miR-204/miR-211 knockdown using antisense inhibitors improved kidney function and reduced renal injury induced by candidemia46 •inhibiting miR-21 upregulation by intraperitoneal injection of antagomirs improved kidney injury and fibrosis23 •delivering antagomirs through other routes, such as intravenous47,48,49 and subcutaneous injection,50,51 has also resulted in inhibitory effects on kidney disease progression
LNAs	•LNAs are structures with improved miRNA bio-stability and inhibitory effects24	•the intraperitoneal delivery of an LNA–modified inhibitor of miR-192 in streptomycin-induced diabetic mouse models could effectively downregulate profibrotic genes and hence attenuate renal fibrosis and improve kidney function52
ASOs	•single-stranded chains of nucleotides complementary to the target gene’s mRNA	•intraperitoneal administration of angiotensinogen53 or mammalian target of rapamycin ASOs54 resulted in effective inhibition of PKD progression •intraperitoneal or intravenous administration of Ki-67- and vascular endothelial growth factor-directed ASOs efficiently inhibiting tumor growth and metastasis in renal cell carcinoma55,56 •subcutaneous injection of naked Kras-silencing ASOs can effectively control the renal fibrosis57 •a reduction in the sulfur content and the use of 2′-O-methoxyethylribose-modified phosphodiester/phosphorthioate chimeric ASOs rather than PS ASOs can help to overcome the preferential ASO distribution to the liver and make them targeted them for kidney58
saRNA	•induces the expression of genes by targeting the promoter59	•saRNA treatment in mouse models of calcium oxalate nephrolithiasis promoted urine calcium reabsorption and lowered both calcium excretion as well as renal calcium oxalate crystals formation by targeting the TRPV5 (epithelial Ca2+ channel TRPV5 mediates calcium transport and reabsorption in kidneys) promoter and activating the gene expression60
shRNAs	•single-strand RNA or DNA targeting a specific gene sequence to silence or regulate its expression	•transarterial administration of a p53 shRNA plasmid in IR mice models has led to the downregulation of glycogen synthase kinase-3β is closely related to IR injury) in epithelial cells of thick ascending limb of the loop of Henle61 •shRNAs can integrate into the DNA through cell infection and this would reduce the variability of transfection efficiency based on the capability of the cells in transfection62
siRNA	•siRNA is double-stranded RNA that recognizes a target mRNA sequence marking the mRNA for degradation. This knockdown activity is highly specific in a way that even with one nucleotide mismatch can stop siRNA inhibitory activity63	•intravenous injection of siRNA targeted to p53 has proved to be advantageous for both prophylactic treatment and rapid treatment of AKI by the short-term inhibition of p53 and with peritubular capillary being the main delivery site64 •the perfusion of the kidney with a cocktail of three different siRNAs targeting C3, RelB, and Fas before transplantation has led to attenuating renal IR injury and extending cold preservation time of donor kidneys65 •in a reversible unilateral ureteral obstruction mice model, delivering siRNA-CD40 to block the co-stimulatory CD40-CD40L signaling pathway reduces the severity of the kidney damage induced by obstructive uropathy66 •to inhibit circular RNA-7 (plays a key role in the pathogenesis of renal cell carcinoma through the PI3K/AKT signaling pathway and by acting as a sponge for miR-139-3p and preventing its inhibitory effects on TAGLN), siRNAs against the junction sites of circRNA-7 was coupled with poly-β-amino ester to form PBAE/si-circRA-7 nanocomplexes, which could successfully inhibit renal cell carcinoma growth and metastasis in vivo67
Aptamer	•single-strand DNA or RNA that bind specifically to target molecules that lead to the regulation on protein level68,69	•RAGE-directed aptamers blocked the binding (the AGE-RAGE interaction stimulates NADPH oxidase–mediated reactive oxygen species generation, resulting in the podocyte damage and kidney disease.) between AGE and RAGE, and had therapeutic effects on diabetic nephropathy in rat models of type 1 diabetes70 as well as MR-associated renal diseases71 •intraperitoneal administration of periostin-binding DNA aptamers has decreased the expression of ECM proteins and attenuated the renal fibrosis in the type I and II diabetic mouse models72 •intravenous administration of a highly selective DNA aptamer, named SW-4b with two hairpins on a big loop, into 786-O xenograft nude mice models resulted in the inhibition of cancer cell growth through cell-cycle arrest at S phase73
circular RNAs	•have a covalently bonded circular structure that makes them more stable than linear RNA •less circular RNA is required to achieve the same effects as mRNA, making it less toxic74	•has not been used for kidney gene therapy so far

AGE, advanced glycation end products; RAGE, advanced glycation end products receptor; LNA, locked nucleic acid.