Erythropoietin has been thought to be secreted to plasma soon after the production because of the difficulty of Western blot analysis and immunohistochemistry. We established the new methods of Western blot analysis and immunohistochemistry. Using the new methods, we investigated the effects of aldosterone and fludrocortisone, an analogue of aldosterone on erythropoietin mRNA and protein production by the kidneys. Aldosterone stimulated Epo and HIF2α mRNA expressions in tubule suspensions and microdissected medullary thick ascending limbs and outer medullary collecting ducts. Western blot analysis showed a recombinant erythropoietin at 34-45 kDa and kidney erythropoietin at 36-40 and 42 kDa, both of which shifted to 22 kDa by deglycosylation. Erythropoietin protein expression was observed in the nephrons but not in the interstitial cells in control condition. Fludrocortisone stimulated erythropoietin mRNA and protein expressions in the distal nephrons, particularly in the intercalated cells of the collecting ducts. These data show that erythropoietin is produced by the nephrons by the regulation of renin-angiotensin-aldosterone system and not by the renal interstitial cells in control condition.

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Background: A new type of glomerulonephritis following a methicillin-resistant Staphylococcus aureus (MRSA) infection has been reported. The purpose of this study is to elucidate the clinicopathological features and the responsiveness to treatment of the disease. Methods: We studied the treatment of 8 patients with glomerulonephritis related to MRSA infection. We observed the eight cases and analyzed clinical features, laboratory findings and histopathological data. Results: On admission, all patients had no renal abnormalities. One to four months after suffering from MRSA infection, severe proteinuria and hematuria developed. Renal biopsy specimens revealed moderate to severe mesangial proliferative glomerulonephritis with various degrees of crescent formation. Immunofluorescence studies showed IgA and C3. Antibiotic therapy was performed in six cases, resulting in successfully reducing the proteinuria in parallel with the decreased activity of MRSA infection in five cases. The other 2 cases received corticosteroid treatment after complete cessation of MRSA infection, but they had a relapse of MRSA infection and later died from sepsis. Conclusions: These results suggested that MRSA-associated glomerulonephritis might respond to antibiotic treatment in most cases. This also indicated that special care must be taken in the application of steroid therapy for the glomerulonephritis with crescents, even though the MRSA infection has gone into an inactive state.

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The kidney is a main site of erythropoietin production in the body. We developed a new method for the detection of Epo protein by deglycosylation-coupled Western blotting. Detection of deglycosylated Epo enables the examination of small changes in Epo production. Using this method, we investigated the effects of angiotensin II (ATII) on Epo production in the kidney. ATII stimulated the plasma Epo concentration; Epo, HIF2α, and PHD2 mRNA expression in nephron segments in the renal cortex and outer medulla; and Epo protein expression in the renal cortex. In situ hybridization and immunohistochemistry revealed that ATII stimulates Epo mRNA and protein expression not only in proximal tubules but also in collecting ducts, especially in intercalated cells. These data support the regulation of Epo production in the kidney by the renin–angiotensin–aldosterone system (RAS).