Yoshikata Morita

Obesity-Mediated Autophagy Insufficiency Exacerbates Proteinuria-induced Tubulointerstitial Lesions

Obesity is an independent risk factor for renal dysfunction in patients with CKDs, including diabetic nephropathy, but the mechanism underlying this connection remains unclear. Autophagy is an intracellular degradation system that maintains intracellular homeostasis by removing damaged proteins and organelles, and autophagy insufficiency is associated with the pathogenesis of obesity-related diseases. We therefore examined the role of autophagy in obesity-mediated exacerbation of proteinuria-induced proximal tubular epithelial cell damage in mice and in human renal biopsy specimens. In nonobese mice, overt proteinuria, induced by intraperitoneal free fatty acid-albumin overload, led to mild tubular damage and apoptosis, and activated autophagy in proximal tubules reabsorbing urinary albumin. In contrast, diet-induced obesity suppressed proteinuria-induced autophagy and exacerbated proteinuria-induced tubular cell damage. Proximal tubule-specific autophagy-deficient mice, resulting from an Atg5 gene deletion, subjected to intraperitoneal free fatty acid-albumin overload developed severe proteinuria-induced tubular damage, suggesting that proteinuria-induced autophagy is renoprotective. Mammalian target of rapamycin (mTOR), a potent suppressor of autophagy, was activated in proximal tubules of obese mice, and treatment with an mTOR inhibitor ameliorated obesity-mediated autophagy insufficiency. Furthermore, both mTOR hyperactivation and autophagy suppression were observed in tubular cells of specimens obtained from obese patients with proteinuria. Thus, in addition to enhancing the understanding of obesity-related cell vulnerability in the kidneys, these results suggest that restoring the renoprotective action of autophagy in proximal tubules may improve renal outcomes in obese patients.

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells.

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain‐deficient mice, unilateral ureteral obstruction (UUO)‐induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.

Fatty acids are novel nutrient factors to regulate mTORC1 lysosomal localization and apoptosis in podocytes

Podocyte apoptosis is a potent mechanism of proteinuria in diabetic nephropathy. More detailed mechanistic insight into podocyte apoptosis is needed to better understand the pathogenesis of diabetic nephropathy. An elevated level of serum free fatty acid (FFA), as well as hyperglycemia, is a clinical characteristic in diabetes, although its causal role in podocyte apoptosis remains unclear. This study examined the effect of three types of FFAs, saturated, monounsaturated and polyunsaturated FFAs, on podocyte apoptosis. Palmitate, a saturated FFA, induced endoplasmic reticulum (ER) stress-dependent apoptosis in podocytes. Oleate, a monounsaturated FFA, and eicosapentaenoic acid (EPA), an ω-3 polyunsaturated FFA did not induce apoptosis; rather, they antagonized palmitate-induced apoptosis. Palmitate activated mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a nutrient-sensing kinase regulating a wide range of cell biology. Furthermore, inhibition of mTORC1 activity by rapamycin or siRNA for Raptor, a component of mTORC1, ameliorated palmitate-induced ER stress and apoptosis in podocytes. Activity of mTORC1 is regulated by upstream kinases and Rag/Ragulator-dependent recruitment of mTOR onto lysosomal membranes. Palmitate activated mTORC1 by enhancing recruitment of mTOR onto lysosomal membranes, which was inhibited by co-incubation with oleate or EPA. Inhibition of mTOR translocation onto lysosomes by transfection with dominant-negative forms of Rag ameliorated palmitate-induced apoptosis. This study suggests that saturated and unsaturated FFAs have opposite effects on podocyte apoptosis by regulating mTORC1 activity via its translocation onto lysosomal membranes, and the results provide a better understanding of the pathogenesis in diabetic nephropathy and a novel role of mTORC1 in cell apoptosis.

Is tubulointerstitial nephritis and uveitis syndrome associated with IgG4-related systemic disease?

A 50-year-old Japanese woman with no remarkable history was admitted because of 1 month minimal fever, weight loss, musculoskeletal pain and progression of renal dysfunction. Physical examination was unremarkable, and no ophthalmologic abnormalities, for example, corneal erosions or uveitis, were identified. Laboratory examination revealed mild normocytic anaemia without eosinophilia, and marked inflammatory signs (erythrocyte sedimentation rate 142 mm/h, C-reactive protein 0.07 g/L, reference <0.001). Although no remarkable urinary abnormalities were identified, renal function deteriorated (serum creatinine 138.7 mmol/L, reference 35.4–70.7, urinary b2-microglobulin 19 862 mg/L, reference <200). Other tests, including serum complements, blood/urine cultures, hepatitis B/C, rheumatoid factor, antinuclear antibodies, anti-double-stranded-DNA antibodies, anti-SS-A/SS-B antibodies and antineutrophil cytoplasmic antibodies, showed negative/normal results. Computed tomography revealed no abnormal findings in the thyroid, lung, liver, kidney, pancreas, lymph nodes and retroperitoneum. A renal biopsy specimen demonstrated marked inflammatory infiltrates (lymphocytes and plasma cells) without granulomas in the tubulointerstitium. Interstitial fibrosis with tubule atrophy was also observed. The glomeruli showed no remarkable abnormalities. Immunofluorescence study showed no marked staining for immunoglobulins or complements on the renal tissue. The diagnosis of acute tubulointerstitial nephritis was made; thus, oral corticosteroid therapy was initiated. A 6 month treatment with corticosteroid markedly improved her symptoms and renal impairment. Eighteen months after corticosteroid withdrawal, she complained of photophobia and pain in both eyes. Ophthalmologic examination revealed bilateral anterior uveitis. No laboratory abnormalities were identified, including chest X-ray, urinalysis and renal function. Topical corticosteroid applied to the eyes gradually improved her eye symptoms. Our patient presented with tubulointerstitial nephritis followed by uveitis, and no specific aetiology of tubulointerstitial nephritis and/or uveitis (e.g. medications, Sjögren’s syndrome or sarcoidosis) was identified; thus, we initially suspected tubulointerstitial nephritis and uveitis (TINU) syndrome. Although uveitis is known to precede, follow, or occur concomitantly with renal disease, its delayed onset in TINU syndrome of up to 14 months has been reported; thus, our patient is thought to be atypical for TINU syndrome. Recent emerging reports suggest that IgG4-related systemic disease can present as tubulointerstitial nephritis. Further, this disease has also been reported to be associated with our patient’s other clinical manifestations, that is, constitutional inflammatory symptoms and uveitis. Therefore, the renal biopsy specimen was stained with anti-IgG4 monoclonal antibody, which revealed that the majority of infiltrated plasma cells expressed IgG4 in the tubulointerstitium, and we finally diagnosed IgG4-related systemic disease. This disease is characterized by significant lymphoplasmacytic infiltration of various organs (e.g. pancreas, extrahepatic bile ducts, salivary glands and lymph nodes) with IgG4-positive plasma cell infiltration and/or high serum concentration of IgG4, and a rapid clinical response to corticosteroid treatment. Further, multi-system involvement over time is the rule rather than the exception in IgG4-related systemic disease; thus, this might explain why uveitis did not occur until 24 months after the onset of tubulointerstitial nephritis in our case. To our knowledge, ours is the first report describing that IgG4-related systemic disease might mimic TINU syndrome. Our study suggests that IgG4-related systemic disease should be considered when patients with tubulointerstitial nephritis and/or uveitis are seen and that IgG4 staining of kidney biopsy specimens and/or the measurement of serum IgG4 levels might be useful in determining the aetiology of these diseases.

Altered Unfolded Protein Response Is Implicated in the Age-Related Exacerbation of Proteinuria-Induced Proximal Tubular Cell Damage

Aging is a dominant risk factor for end-stage renal disease. We analyzed the mechanism involved in age-related exacerbation of proteinuria-induced proximal tubular cell (PTC) damage by focusing on endoplasmic reticulum-related unfolded protein response (UPR). After equal-degree induction of proteinuria in 24-month-old (aged) and 3-month-old (young) mice by intraperitoneal free fatty acid-bound albumin overload, tubulointerstitial lesions were more severe in aged than in young mice. In aged PTCs, proteinuria-induced cell-adaptive UPR resulting from induction of the molecular chaperone BiP was significantly suppressed, whereas proapoptotic UPR with CHOP overexpression was enhanced. Treatment with the exogenous molecular chaperone tauroursodeoxycholic acid (TUDCA) ameliorated proteinuria-induced tubulointerstitial lesions and PTC apoptosis in aged mice. Among the three UPR branches, alterations in the inositol-requiring 1α (IRE1α) pathway, but not the activating transcription factor 6 or PERK pathway, were associated with impaired BiP induction in aged kidneys. Moreover, siRNA-mediated suppression of BiP and IRE1α exacerbated free fatty acid-bound albumin-induced apoptosis in cultured PTCs, whereas siRNA-mediated CHOP suppression ameliorated apoptosis. Finally, proteinuria-induced BiP induction in PTCs was diminished in kidney specimens from elderly patients. These results indicate that maladaptive UPRs are involved in proteinuria-induced tubulointerstitial lesions exacerbation in aged kidneys, and that supplementation of chaperones may be used to treat elderly patients with persistent proteinuria. These results should improve understanding of cell vulnerability in aged kidneys.

Anti-neutrophil cytoplasmic antibodies-related necrotising crescentic glomerulonephritis in a patient with rheumatoid arthritis.

Renal dysfunction and urinary abnormalities are frequently observed in the patients with rheumatoid arthritis (RA), which are usually related to drug toxicity or secondary amyloidosis. 1 Here we report a patient with RA who developed myeloperoxidase (MPO)-antineutrophil cytoplasmic antibody (ANCA)-related renal vasculitis, that is, necrotizing crescentic glomerulonephritis. A 30-year-old Japanese woman with a 2-year history of RA was admitted because of haematuria and mild renal dysfunction. She was diagnosed as having RA because of symmetrical polyarthritis and a high titre of rheumatoid factor, and she had started to receive gold salts, non-steroidal antiinflammatory drugs (NSAIDs), and oral prednisolone, but her disease activity had not been controlled well. One year prior to the admission, she was noticed to have haematuria without renal dysfunction (serum creatinine, 0.6 mg/dL). The urinary abnormality had persisted, and serum creatinine increased to 1.5 mg/dL on admission. Physical examination was unremarkable except for symmetrical polyarthritis (Steinbrocker grading II). The urinalysis disclosed daily proteinuria of 0.5 g and haematuria (4–5 erythrocytes/high-power fields) without any remarkable leucocytes or casts. The serological test showed elevation of C-reactive protein (5.46 mg/dL), hypergammaglobulinaemia, and normal complement concentrations. Rheumatoid factor was 262 IU/mL and RA haemagglutination was 1:320. Anti-nuclear antibodies, anti-double-stranded-DNA antibody, and anti-hepatitis B/C antibodies were negative. Renal biopsy revealed global sclerosis in 14 glomeruli among the total of 24 glomeruli examined. Segmental tuft necrosis and fibrocellular crescents were observed in eight glomeruli. The remaining two glomeruli showed minor abnormalities. Mild tubular atrophy, interstitial cell infiltration, and fibrosis were also observed. Immunofluorescence microscopic examination did not show any deposition of immunoglobulins or complements. Further, a high titre of MPO-ANCA (497 EU, normal < 10 EU) was identified. She was treated with methylprednisolone i.v. followed by oral prednisolone therapy. Her serum creatinine decreased to 1.2 mg/dL and remained stable, and MPO-ANCA became undetectable after 15 months of treatment. The present report shows the occurrence of MPOANCA-related renal vasculitis, that is, necrotising crescentic glomerulonephritis, in a patient with active RA of short duration. Renal vasculitis complicating RA has been thought to be rare, and there are few data on its clinical features. MPO-ANCA is detected in approximately 10% of RA patients; 2 however, few patients have been described with RA associated with MPO-ANCA-related necrotising glomerulonephritis. 3–5 Therefore, it is unclear whether this association is a mere coincidence or an inherent renal manifestation of RA. Our patient had active arthritis, but she did not show any typical manifestations of MPO-ANCArelated angiitis, such as weight loss, high fever, fatigue, or active nephritic urinary abnormalities; thus, we initially underrated her renal lesions. We suspect that her treatment for RA, such as gold salts, NSAIDs and corticosteroids, had modified her clinical manifestations. This study highlights the importance of renal biopsy in RA patients presenting with any continuing urinary abnormality or renal dysfunction.

Diffuse alveolar hemorrhage in lupus nephritis complicated by microscopic polyangiitis

Diffuse alveolar hemorrhage (DAH) is a rare but fatal complication in patients with systemic lupus erythematosus (SLE). We describe a case of a 74-year-old woman who presented with DAH as an initial presentation of SLE. She also had microscopic polyangiitis clinically manifesting as crescentic glomerulonephritis and purpura with positive myeloperoxidase (MPO)-antineutrophil cytoplasmic antibodies (ANCA). The patient transiently improved when treated with plasma exchange and methylprednisolone pulse therapy; however, she died of recurrent pulmonary hemorrhage and concurrent cryptococcal pneumonia. This case indicates that MPO-ANCA is associated with severe organ involvement such as pulmonary hemorrhage and crescentic glomerulonephritis in SLE.

Oral glucose-stimulated serum C-peptide predicts successful switching from insulin therapy to liraglutide monotherapy in Japanese patients with type 2 diabetes and renal impairment.

In Japan, liraglutide was recently approved for patients with type 2 diabetes. To our knowledge, there are no markers predicting successful switching from insulin therapy to liraglutide monotherapy in Japanese patients with type 2 diabetes and renal impairment. We therefore assessed clinical characteristics predicting successful switching.

Focal Segmental Glomerular Sclerosis Ameliorated by Long-term Hemodialysis Therapy with Low-density Lipoprotein Apheresis.

We report a case involving a 43-year-old Japanese woman with steroid-resistant focal segmental glomerular sclerosis (FSGS) and severe renal dysfunction, which was ameliorated by low-density lipoprotein apheresis (LDL-A). She had been treated with steroid therapy, but had experienced anuria for over 10 weeks and required hemodialysis. She was then treated with LDL-A, which resulted in improved urinary protein excretion and renal function. Her renal function recovered after 97 days of hemodialysis therapy. This case suggests that LDL-A may represent an effective rescue treatment in patients with FSGS and long-term anuria.