Expression in Mouse Kidney of Membrane Copper Transporters Atp7a and Atp7b

Abstract

Copper is essential for activity of many enzymes, but is toxic in excess. Several copper proteins are required for copper homeostasis. ATP7A and ATP7B are genes encoding membrane copper transporters. ATP7A, defective in Menkes disease (MNK), is expressed in many tissues involved primarily in copper uptake from dietary sources. ATP7B, defective in Wilson disease (WND), is essential for copper excretion. Although MNK patients have a copper deficiency in most tissues, copper accumulates in proximal tubules in the kidney. WND patients also have copper accumulation in the proximal tubules. In some WND patients this copper accumulation may result in tubular dysfunction, resulting in the increased excretion of low molecular weight substances (e.g. amino acids and calcium). In mouse, we have demonstrated, by in situ hybridization, the expression pattern in the kidney of mouse orthologues, Atp7a and Atp7b, and have confirmed Atp7b expression by immunohistochemistry. Both Atp7a and Atp7b are expressed in glomeruli; however, Atp7b is also seen in the kidney medulla. This suggests that glomeruli are responsible for regulating copper levels in the filtrate. In WND patients, urinary copper levels are extremely high suggesting Atp7b in the loops of Henle may have a role in copper reabsorption.

Intracellular targeting of copper-transporting ATPase ATP7A in a normal andAtp7b−/−kidney

“…Previously, significant discrepancies in the distribution of ATP7A have been reported (see Introduction). Our data agreed with some reports (6,19) but contradicted others (17); consequently, we investigated the possible reasons for such discrepancies in more detail.…”

“…In situ hybridization of ATP7A mRNA in the mouse kidney showed strong staining in proximal tubules (19), in contrast to another study in which the glomerulus showed the strongest staining and proximal tubules were stained weakly (17). In immunochemistry experiments using control and brindled mice (an animal model of Menkes disease), ATP7A was detected in the proximal and distal tubules but not in the glomerulus (6).…”

“…Previous studies have suggested that another copper-transporting ATPase, ATP7B, is also expressed in kidneys (17,31) and therefore may contribute to copper homeostasis. Our anti-ATP7B antibody was insufficiently sensitive to detect distribution of ATP7B in tissue of adult mice (although signal was detected in kidney of young animals and in primary cell culture; our data, not shown).…”

“…No staining of the transgene product was seen in the proximal tubules. ATP7B distribution was investigated only in one study, and both mRNA and protein were found in the glomerulus and inner and outer medulla (17).…”

The multi-layered regulation of copper translocating P-type ATPases

“…The malabsorption of Cu in Menkes disease results in Cu accumulation in intestinal cells, placenta, mammary tissue and the kidneys and deficiency in the brain, liver and serum. This leads to disrupted neurological and connective tissue development, causing mental retardation and neurodegeneration and usually results in early childhood death (Danks 1995;Kaler 1998;Moore and Cox 2002). Non-functional WND leads to reduced hepatic Cu excretion into bile, reduced ceruloplasmin in the serum and subsequent hepatic and brain Cu accumulation in Wilson disease patients.…”