Albumin stimulates cell growth, l-arginine transport, and metabolism to polyamines in human proximal tubular cells.
BACKGROUND
Pure albumin stimulates proximal tubular epithelial cell (PTEC) proliferation, and may have a role in homeostasis in health, as well as in disrupted PTEC turnover in proteinuric nephropathies. We investigated a role for arginine and its metabolites, the polyamines, in this process, given the ability of polyamines to trigger proliferation in other mammalian cells.


METHODS
[(3)H]-L-arginine uptake was examined after incubation with 20 mg/mL recombinant human serum albumin (rHSA) in HK-2 PTEC monolayers. Nitric oxide synthase (NOS) and arginase activity was measured; NOS, arginase, and ornithine decarboxylase (ODC) expression was identified by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Polyamine synthesis and intracellular amino acid concentrations were compared using high-performance liquid chromatography, and cell growth measured by [(3)H]-thymidine incorporation.


RESULTS
In HK-2 PTEC exposed to 20 mg/mL rHSA for 24 hours, cell proliferation as determined by [(3)H]-thymidine incorporation was increased. In parallel, L-arginine transport capacity was increased in a dose- and time-dependent manner. This effect was specific to rHSA, and was not seen with transferrin or immunoglobulin G. The intracellular concentration of L-arginine remained unchanged, although L-ornithine was increased with rHSA incubation. rHSA up-regulated type II arginase mRNA, and increased arginase activity, although no difference in nitric oxide synthase expression or activity was seen. ODC mRNA was increased, as were intracellular polyamine concentrations. alpha-Difluoromethylornithine (DFMO), an ODC inhibitor, reduced intracellular polyamine concentrations and rHSA-induced cell proliferation to control levels.


CONCLUSIONS
The arginine-ornithine-polyamine pathway appears enhanced in PTEC incubated with rHSA and is involved in cellular proliferation; this may offer novel approaches to understanding progressive proteinuric nephropathies.
Ashman
Neil
N
Department of Clinical Chemistry, University of Liverpool, Liverpool, United Kingdom. neil.ashman@bartsandthelondon.nhs.uk
Harwood
Steven M
SM
Kieswich
Julius
J
Allen
David A
DA
Roberts
Norman B
NB
Mendes-Ribeiro
A Claudio
AC
Yaqoob
Muhammad M
MM
D001119:Arginase / Q000235:genetics / Q000378:metabolism; D001120:Arginine / Q000378:metabolism*; D001483:Base Sequence; D001693:Biological Transport, Active; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000518:Eflornithine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006706:Homeostasis; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009952:Ornithine / Q000378:metabolism; D009955:Ornithine Decarboxylase / Q000235:genetics; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000008:administration & dosage; D012709:Serum Albumin / Q000008:administration & dosage*; D015854:Up-Regulation
D004791:Enzyme Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012709:Serum Albumin; D001120:Arginine; D009952:Ornithine; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C477631:ARG2 protein, human; D001119:Arginase; D009955:Ornithine Decarboxylase; D000518:Eflornithine