Abstract
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.
Highlights
The prevalence of chronic kidney disease (CKD) is estimated to be 8–16% of the global population [1], and the presence of CKD is intimately associated with large increases in both endstage kidney disease and cardiovascular disease risk [2]
One major cause of CKD is the disruption of genes that are expressed in specific cells of the renal tubules; this can result in several different diseases, e.g., Fanconi syndrome, Bartter syndrome, Gitelman syndrome, and Dent disease [3, 4, 5, 6]
We focused on representative genes normally expressed in specific kidney tubule structures: sodium-dependent phosphate transporter 2 (NPT2a; SLC34A1) in the proximal tubule [15], Targeting gene expression to kidney cells sodium-potassium chloride cotransporter (NKCC2; SLC12A1) in the thick ascending limb of Henle (TALH) [16], and aquaporin 2 (AQP2) in the collecting duct or distal tubule [16]
Summary
The prevalence of chronic kidney disease (CKD) is estimated to be 8–16% of the global population [1], and the presence of CKD is intimately associated with large increases in both endstage kidney disease and cardiovascular disease risk [2]. One approach is to modify the existing viruses to develop artificial transduction vehicles; many of these are accumulated in the liver [20, 21] Another approach is direct administration to the target organ. Direct administration into deep tissues is invasive, and it is difficult to induce genes in the entire tissues, or at the desired sites, of the target organ. For these reasons, targeted gene expression is currently limited to the surface tissues of such organs as the eyes and the respiratory tract. Direct surgical access to a target organ does not facilitate the selection of specific cell types, because most organs contain many different types of cells within close proximity
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