Targeting gene expression to specific cells of kidney tubules in vivo, using adenoviral promoter fragments

<div><p>Although techniques for cell-specific gene expression via viral transfer have advanced, many challenges (e.g., viral vector design, transduction of genes into specific target cells) still remain. We investigated a novel, simple methodology for using adenovirus transfer to target specific cells of the kidney tubules for the expression of exogenous proteins. We selected genes encoding sodium-dependent phosphate transporter type 2a (NPT2a) in the proximal tubule, sodium-potassium-2-chloride cotransporter (NKCC2) in the thick ascending limb of Henle (TALH), and aquaporin 2 (AQP2) in the collecting duct. The promoters of the three genes were linked to a GFP-coding fragment, the final constructs were then incorporated into an adenovirus vector, and this was then used to generate gene-manipulated viruses. After flushing circulating blood, viruses were directly injected into the renal arteries of rats and were allowed to site-specifically expression in tubule cells, and rats were then euthanized to obtain kidney tissues for immunohistochemistry. Double staining with adenovirus-derived EGFP and endogenous proteins were examined to verify orthotopic expression, i.e. “adenovirus driven NPT2a-EGFP and endogenous NHE3 protein”, “adenovirus driven NKCC2-EGFP and endogenous NKCC2 protein” and “adenovirus driven AQP2-EGFP and endogenous AQP2 protein”. Owing to a lack of finding good working anti-NPT2a antibody, an antibody against a different protein (sodium-hydrogen exchanger 3 or NHE3) that is also specifically expressed in the proximal tubule was used. Kidney structures were well-preserved, and other organ tissues did not show EGFP staining. Our gene transfer method is easier than using genetically engineered animals, and it confers the advantage of allowing the manipulation of gene transfer after birth. This is the first method to successfully target gene expression to specific cells in the kidney tubules. This study may serve as the first step for safe and effective gene therapy in the kidney tubule diseases.</p></div

Immunohistochemistry of the kidneys.

<p>a. Paraffin-embedded sections of the kidneys infected with CAG-EGFP adenovirus. The arrow indicates glomerulus. Adenovirus-derived EGFP was stained in brown. b and c. Paraffin embedded sections of the kidney infected with NKCC2DI-EGFP adenovirus. Adenovirus-derived EGFP is shown in brown and endogenous NKCC2 is shown in pink. e and f. Immunostaining of frozen kidney sections infected with CAG-EGFP is shown in e and NKCC2DI-EGFP is shown in f. e.Green indicates CAG promoter derived EGRP and f. Green indicates NKCC2 promoter-derived EGFP. f. Red indicates endogenous NKCC2. e and f. Blue indicates nucleus.</p

Immunostaining of the kidneys from adenovirus administered rats.

<p>a. EGFP staining of the kidneys in rats received CAG-EGFP adenovirus (brown). b and c. EGFP staining of the kidney in rats received NKCC2DI-EGFP (b, brown). The adjacent section of the kidney was stained with endogenous NKCC2 (c, blue). d and e. EGFP staining of the kidney in rats received NKCC2 pvu-EGPF adenovirus (d, brown). The adjacent section was stained with NKCC2 (e, blue). f and g. EGFP stating of the kidney in rats received pNKCC2-EGPF adenovirus (f, brown). The adjacent section was stained with NKCC2 (g, blue). Scale bar: 1 cm.</p

Designs of cloned pNKCC2, NPT2a, and AQP2 promoters.

<p>a. Three different NKCC2 promoters used in this study. Transgene expression patterns were compared among the constructs, using these promoters. b. NPT2a promoter. c. AQP2 promoter.</p