A homozygous hypomorphic BNIP1 variant causes an increase in autophagosomes and reduced autophagic flux and results in a spondylo-epiphyseal dysplasia

TY - JOUR

T1 - A homozygous hypomorphic BNIP1 variant causes an increase in autophagosomes and reduced autophagic flux and results in a spondylo-epiphyseal dysplasia

AU - Holling, Tess

AU - Bhavani, Gandham S

AU - von Elsner, Leonie

AU - Shah, Hitesh

AU - Kausthubham, Neethukrishna

AU - Bhattacharyya, Shaila S

AU - Shukla, Anju

AU - Mortier, Geert R

AU - Schinke, Thorsten

AU - Danyukova, Tatyana

AU - Pohl, Sandra

AU - Kutsche, Kerstin

AU - Girisha, Katta M

N1 - © 2022 The Authors. Human Mutation published by Wiley Periodicals LLC.

PY - 2022/5

Y1 - 2022/5

N2 - BNIP1 (BCL2 interacting protein 1) is a soluble N-ethylmaleimide-sensitive factor-attachment protein receptor involved in ER membrane fusion. We identified the homozygous BNIP1 intronic variant c.84+3A>T in the apparently unrelated patients 1 and 2 with disproportionate short stature. Radiographs showed abnormalities affecting both the axial and appendicular skeleton and spondylo-epiphyseal dysplasia. We detected ~80% aberrantly spliced BNIP1 pre-mRNAs, reduced BNIP1 mRNA level to ~80%, and BNIP1 protein level reduction by ~50% in patient 1 compared to control fibroblasts. The BNIP1 ortholog in Drosophila, Sec20, regulates autophagy and lysosomal degradation. We assessed lysosome positioning and identified a decrease in lysosomes in the perinuclear region and an increase in the cell periphery in patient 1 cells. Immunofluorescence microscopy and immunoblotting demonstrated an increase in LC3B-positive structures and LC3B-II levels, respectively, in patient 1 fibroblasts under steady-state condition. Treatment of serum-starved fibroblasts with or without bafilomycin A1 identified significantly decreased autophagic flux in patient 1 cells. Our data suggest a block at the terminal stage of autolysosome formation and/or clearance in patient fibroblasts. BNIP1 together with RAB33B and VPS16, disease genes for Smith-McCort dysplasia 2 and a multisystem disorder with short stature, respectively, highlight the importance of autophagy in skeletal development.

AB - BNIP1 (BCL2 interacting protein 1) is a soluble N-ethylmaleimide-sensitive factor-attachment protein receptor involved in ER membrane fusion. We identified the homozygous BNIP1 intronic variant c.84+3A>T in the apparently unrelated patients 1 and 2 with disproportionate short stature. Radiographs showed abnormalities affecting both the axial and appendicular skeleton and spondylo-epiphyseal dysplasia. We detected ~80% aberrantly spliced BNIP1 pre-mRNAs, reduced BNIP1 mRNA level to ~80%, and BNIP1 protein level reduction by ~50% in patient 1 compared to control fibroblasts. The BNIP1 ortholog in Drosophila, Sec20, regulates autophagy and lysosomal degradation. We assessed lysosome positioning and identified a decrease in lysosomes in the perinuclear region and an increase in the cell periphery in patient 1 cells. Immunofluorescence microscopy and immunoblotting demonstrated an increase in LC3B-positive structures and LC3B-II levels, respectively, in patient 1 fibroblasts under steady-state condition. Treatment of serum-starved fibroblasts with or without bafilomycin A1 identified significantly decreased autophagic flux in patient 1 cells. Our data suggest a block at the terminal stage of autolysosome formation and/or clearance in patient fibroblasts. BNIP1 together with RAB33B and VPS16, disease genes for Smith-McCort dysplasia 2 and a multisystem disorder with short stature, respectively, highlight the importance of autophagy in skeletal development.

KW - Animals

KW - Autophagosomes/metabolism

KW - Autophagy/genetics

KW - Drosophila

KW - Homozygote

KW - Humans

KW - Lysosomes/metabolism

KW - Proto-Oncogene Proteins c-bcl-2/genetics

U2 - 10.1002/humu.24368

DO - 10.1002/humu.24368

M3 - SCORING: Journal article

C2 - 35266227

VL - 43

SP - 625

EP - 642

JO - HUM MUTAT

JF - HUM MUTAT

SN - 1059-7794

IS - 5

ER -