Bioengineered Implantation of Megalin-Expressing Cells

Abstract

Abstract.Patients who have renal failure and are on dialysis therapy experience serious complications caused by low-molecular-weight uremic toxin proteins normally filtered by glomeruli and metabolized by proximal tubule cells (PTC). Dialysis-related amyloidosis is one such complication induced by systemic deposition of amyloid proteins derived from 12-kD ␤ 2 -microglobulin (␤ 2 -m). Despite the use of high-flux membrane hemodialysis devices and direct absorbent columns, the removal of ␤ 2 -m is suboptimal, because the effects are transient and insufficient. Megalin is expressed in the apical membranes of PTC and recognized as a multiligand endocytic receptor that binds numerous low-molecular-weight proteins, including ␤ 2 -m. This study tested the feasibility of an intracorporeal therapeutic model of continuous ␤ 2 -m removal using megalin-expressing cell implantation. By cell association and degradation assays, rat yolk sac-derived L2 cells were identified to internalize and degrade ␤ 2 -m via megalin. The cells were effectively implanted within the subcutaneous tissues of nude mice using a type I collagen scaffold and a method inducing local angiogenesis. After nephrectomy and intraperitoneal injection with 125 I-␤ 2 -m, it was found that the implanted cells took up the labeled ligand, efficiently removing it from the blood. Bioengineered implantation of megalin-expressing cells may represent a new supportive therapy for dialysis patients to compensate for the loss of renal protein metabolism and remove uremic toxin proteins.

Dialysis at a Crossroads

“…Therefore, the prospects for development of novel renal replacement therapies are bright. Innovative therapies that are currently being considered include development of wearable artificial kidneys (38), hybrid renal-assist devices that combine cellular therapy with plasma separation (39), membraneless dialysis (40), and genetic engineering to increase cellular detoxification potential (41). Nanotechnology may be applicable to dialytic therapies (42).…”

“…Genetic engineering approaches may more robustly remove specific toxins. For example, implantation of bioengineered megalinexpressing cells would be expected to enhance greatly the clearance of low molecular weight proteins, and the engineering of organic anion and cation transporter would be expected to modulate clearance of these toxic solutes (41).…”

Stem Cell Approaches for the Treatment of Renal Failure

“…In the case of ␤2M, accumulation in ESRD patients at up to 40 times the normal serum concentration often leads to the development of debilitating arthritis, as amyloid deposits of ␤2M build up in their joints (Gejyo, 2000). Saito et al (2003) have demonstrated the feasibility of using a cellular implant for continuous degradation of low molecular weight proteins such as ␤2M. Working in nude mice, they first implanted a collagen sponge impregnated with basic fibroblast growth factor to promote vascularization and subsequently introduced megalin-expressing cells into the newly vascularized structure.…”

“…Working in nude mice, they first implanted a collagen sponge impregnated with basic fibroblast growth factor to promote vascularization and subsequently introduced megalin-expressing cells into the newly vascularized structure. The cells (L2), derived from a rat yolk sac carcinoma, were shown to take up and degrade circulating ␤2M, leading to a 40% reduction in the steady-state level of this uremic toxin in nephrectomized animals (Saito et al, 2003). It should be noted that this result was only achieved with an estimated 7 ϫ 10 9 cells in the implant, representing approximately 30% of the mouse body weight.…”

Urinary Iron Excretion is Associated with Urinary Full-Length Megalin and Renal Oxidative Stress in Chronic Kidney Disease

“…It plays a physiologically important role in the endocytic reabsorption of glomerular-filtered substances, such as albumin and low-molecular weight proteins including non-transferrin iron-carrier proteins in PTECs [6, 14]. Glomerular-filtered low-molecular weight proteins, such as α 1 -microglobulin [15], β 2 -microglobulin [16], and liver-type fatty acid binding protein [17], are clinical markers for the endocytic function of megalin. In addition, megalin mediates the uptake of nephrotoxic substances by PTECs, leading to development of CKD [18] and AKI [19].…”