Anti-LRP2 Nephropathy

Renal Proximal Tubule Cell-specific Megalin Deletion Does Not Affect Atherosclerosis But Induces Tubulointerstitial Nephritis in Mice Fed Western Diet

Background

Pharmacological inhibition of megalin (also known as low-density lipoprotein receptor-related protein 2: LRP2) attenuates atherosclerosis in hypercholesterolemic mice. Since megalin is abundant in renal proximal tubule cells (PTCs), the purpose of this study was to determine whether PTC-specific deletion of megalin reduces hypercholesterolemia-induced atherosclerosis in mice.

Methods

Female Lrp2 f/f mice were bred with male Ndrg1-Cre ERT2 +/0 mice to develop PTC-LRP2 +/+ and -/- littermates. To study atherosclerosis, all mice were to bred to an LDL receptor -/- background and fed a Western diet to induce atherosclerosis.

Results

PTC-specific megalin deletion did not attenuate atherosclerosis in LDL receptor -/- mice in either sex. Serendipitously, we discovered that PTC-specific megalin deletion led to interstitial infiltration of CD68+ cells and tubular atrophy. The pathology was only evident in male PTC-LRP2 -/- mice fed the Western diet, but not in mice fed a normal laboratory diet. Renal pathologies were also observed in male PTC-LRP2 -/- mice in an LDL receptor +/+ background fed the same Western diet, demonstrating that the renal pathologies were dependent on diet and not hypercholesterolemia. By contrast, female PTC-LRP2 -/- mice had no apparent renal pathologies. In vivo multiphoton microscopy demonstrated that PTC-specific megalin deletion dramatically diminished albumin accumulation in PTCs within 10 days of Western diet feeding. RNA sequencing analyses demonstrated the upregulation of inflammation-related pathways in kidney.

Conclusions

PTC-specific megalin deletion does not affect atherosclerosis, but leads to tubulointerstitial nephritis in mice fed Western diet, with severe pathologies in male mice.

Tubular basement membrane deposits after allogeneic hematopoietic stem cell transplantation

BACKGROUND

Extraglomerular immune complex deposition is rare and only a few membranous nephropathy cases with tubular basement membrane deposits have been reported following allogeneic hematopoietic stem cell transplantation.

CASE PRESENTATION

We reported a 56-year-old man with increased serum creatinine after allogeneic hematopoietic stem cell transplantation who underwent a renal biopsy. Tubular interstitial nephritis was identified on light microscope. The unique histologic features were diffuse tubular basement membrane immune complex deposition detected by both immunofluorescence and electron microscopy, while the glomerular involvement was inconspicuous. The differential diagnosis from other forms of tubular basement membrane deposition is discussed.

CONCLUSION

Diffuse granular tubular basement membrane immune complex deposition with minimal glomerular involvement is also a manifestation of renal complication in hematopoietic stem cell transplantation recipient. However, the exact mechanism and target antigen remains unknown.

Antibrush Border Antibody Disease: A Case Report and Literature Review

Anti-brush border antibody (ABBA) disease, also called anti-low-density lipoprotein receptor-related protein 2 (anti-LRP2) nephropathy, occurs due to the formation of antibodies against brush border antigens of the renal proximal convoluted tubule. We report a case of ABBA disease in a male farmer in his 30s who presented with 2 years of polyuria, dysuria, nocturia, and urinary urgency. He described a history of long-term occupational exposure to pesticides and silica, evolving into possible pneumoconiosis, and prior pulmonary tuberculosis. At presentation, he had reduced kidney function (serum creatinine 3.6 mg/dL) with hyponatremia, hypokalemia, hypophosphatemia, a normal anion gap, metabolic acidosis, and respiratory acidosis, and 2.2 g/day of urine proteinuria. The kidney biopsy was consistent with ABBA, showing amorphous immune-deposits in the tubular basement membrane and strong positivity on indirect immunofluorescence in the brush border of the proximal tubules. The trigger for production of ABBA is still unknown, but it may be associated with chronic conditions such as pulmonary tuberculosis and occupational exposures such as silica and pesticides, as seen in the patient in this report. Most cases do not respond to immunosuppression, and the prognosis is poor.

Anti-LDL Receptor-Related Protein 2 Nephropathy with Synchronous Primary Kidney Extranodal Marginal Zone Lymphoma

Introduction

Anti-LDL receptor-related protein 2 (anti-LRP2) nephropathy is a rare but progressive form of autoimmune-mediated tubulointerstitial nephritis and glomerular disease, characterized by a classic pattern of immune complex deposition in the kidney. A theoretic link between autoimmune disease and lymphoproliferative diseases exists, and therefore, in some cases autoimmune-mediated inflammation and lymphoproliferative neoplasm can co-exist in the same site.

Case Presentation

An elderly man presented with 6 months of weight loss and fatigue. Subsequent workup showed an elevated serum creatinine and subnephrotic range proteinuria. Kidney biopsy was performed which revealed anti-LRP2 nephropathy with concurrent primary kidney extranodal marginal zone lymphoma. He was subsequently treated with rituximab but remains dialysis-dependent (12 months after his initial diagnosis, at time of publication of this report).

Conclusion

We discuss the bidirectional relationship between autoimmune disease and lymphoma in the kidney, along with a brief review of the literature pertaining to these rare lesions. Our case report highlights the diagnostic difficulties faced by pathologists when encountering this entity. We also attempt to spread awareness about the co-existence of tubulointerstitial inflammation and lymphoproliferative disorder, which may be under-recognized.