Severe kidney dysfunction in sialidosis mice reveals an essential role for neuraminidase 1 in reabsorption
Ikhui Kho, Ekaterina P. Demina, Xuefang Pan, Irene Londono, Christopher W. Cairo, Luisa Sturiale, Angelo Palmigiano, Angela Messina, Domenico Garozzo, Roth-Visal Ung, Fabrice Mac-Way, Éric Bonneil, Pierre Thibault, Mathieu Lemaire, Carlos R. Morales, Alexey V. Pshezhetsky
Ikhui Kho, Ekaterina P. Demina, Xuefang Pan, Irene Londono, Christopher W. Cairo, Luisa Sturiale, Angelo Palmigiano, Angela Messina, Domenico Garozzo, Roth-Visal Ung, Fabrice Mac-Way, Éric Bonneil, Pierre Thibault, Mathieu Lemaire, Carlos R. Morales, Alexey V. Pshezhetsky
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Research Article Genetics Nephrology

Severe kidney dysfunction in sialidosis mice reveals an essential role for neuraminidase 1 in reabsorption

Abstract

Sialidosis is an ultra-rare multisystemic lysosomal disease caused by mutations in the neuraminidase 1 (NEU1) gene. The severe type II form of the disease manifests with a prenatal/infantile or juvenile onset, bone abnormalities, severe neuropathology, and visceromegaly. A subset of these patients present with nephrosialidosis, characterized by abrupt onset of fulminant glomerular nephropathy. We studied the pathophysiological mechanism of the disease in 2 NEU1-deficient mouse models, a constitutive Neu1-knockout, Neu1ΔEx3, and a conditional phagocyte-specific knockout, Neu1Cx3cr1ΔEx3. Mice of both strains exhibited terminal urinary retention and severe kidney damage with elevated urinary albumin levels, loss of nephrons, renal fibrosis, presence of storage vacuoles, and dysmorphic mitochondria in the intraglomerular and tubular cells. Glycoprotein sialylation in glomeruli, proximal distal tubules, and distal tubules was drastically increased, including that of an endocytic reabsorption receptor megalin. The pool of megalin bearing O-linked glycans with terminal galactose residues, essential for protein targeting and activity, was reduced to below detection levels. Megalin levels were severely reduced, and the protein was directed to lysosomes instead of the apical membrane. Together, our results demonstrated that desialylation by NEU1 plays a crucial role in processing and cellular trafficking of megalin and that NEU1 deficiency in sialidosis impairs megalin-mediated protein reabsorption.

Authors

Ikhui Kho, Ekaterina P. Demina, Xuefang Pan, Irene Londono, Christopher W. Cairo, Luisa Sturiale, Angelo Palmigiano, Angela Messina, Domenico Garozzo, Roth-Visal Ung, Fabrice Mac-Way, Éric Bonneil, Pierre Thibault, Mathieu Lemaire, Carlos R. Morales, Alexey V. Pshezhetsky

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Figure 4

Pathological changes in glomerular and tubular cells in Neu1ΔEx3 and Neu1Cx3cr1ΔEx3 mice.

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Pathological changes in glomerular and tubular cells in Neu1ΔEx3 and Neu...
(A) Kidneys of Neu1ΔEx3 mice contain numerous enlarged electron-lucent lysosomes (L) filled with multilamellar structures (black arrowhead) in the proximal convoluted tubule (PCT) and multivesicular bodies (yellow arrowheads) in the lysosomal compartments of the distal convoluted tubules (DCT). Small irregularly shaped mitochondria with fragmented cristae (M) are found throughout the PCT and DCT of Neu1ΔEx3 and Neu1Cx3cr1ΔEx3 mice. In the DCT of Neu1Cx3cr1ΔEx3 mice, mitochondria are dissociated from the distorted basolateral plasma membrane (white arrows). (B) In the glomeruli of Neu1ΔEx3 mice, the podocytes (P) and mesangial cells (M) are severely vacuolated. Higher magnification of podocytes shows multivesicular structures and osmiophilic deposits (yellow arrowhead). The podocyte foot processes (F), which form a discontinuous lining for the inner aspect of the WT glomerular basement membrane, are widely effaced in both Neu1ΔEx3 and Neu1Cx3cr1ΔEx3 mice (black arrows). All transmission electron microscopy panels show representative images taken for 3 WT, 3 Neu1ΔEx3, and 2 Neu1Cx3cr1ΔEx3 mice. Scale bars equal 1 μm (A), 2 μm in glomeruli and 0.2 μm in high-magnification images of podocytes (B). C, capillaries; U, urinary space; E, endothelium. (C) Endothelial cells of the proximal convoluted renal tubules in Neu1ΔEx3 mice reveal accumulation of P62+ and LC3+ puncta, consistent with impaired autophagy and increased phosphorylation (Ser240/244) of S6 ribosomal protein substrate of mTOR complex 1 (mTORC1). Scale bars: 10 μm (left and middle), 1 μm (right). Graph shows relative areas stained with antibodies against P62, LC3, and Ser240/244 S6 quantified with ImageJ. Individual values, means, and SD are shown (n = 3). P values were calculated with multiple unpaired 2-tailed t tests. (D) Immunoblotting of kidney proteins verifies increase in P62, LC3, and Ser240/244 levels. Graph shows bands intensities, quantified with ImageJ software and normalized to the intensities of tubulin immunoreactive bands. Individual values, means, and SD are shown (n = 3). P values were calculated with multiple unpaired 2-tailed t tests.