Pathogenic variants in BORCS5 cause a spectrum of neurodevelopmental and neurodegenerative disorders with lysosomal dysfunction
Niccolò E. Mencacci, Georgia Minakaki, Reza Maroofian, Raffaella De Pace, Adeline Paimboeuf, Tiago Branco Fonseca, Tatiana Abramova, Patrick Shannon, David Chitayat, Francesca Magrinelli, Wesley J. Peng, Diptaman Chatterjee, Sara H. Eldessouky, Julia Baptista, Tamas Marton, Julie Vogt, Juan Dario Ortigoza-Escobar, Loreto Martorell, Marta Gómez-Chiari, Ingrid M. Wentzensen, Erik-Jan Kamsteeg, Maha S. Zaki, Annarita Scardamaglia, Giovanni Zifarelli, Zuhair Nasser Al-Hassnan, Elka Miller, Shiri Shinar, Lova S. Matsa, Sri Hari Chandan Appikonda, Ghada A. Otaify, Khalid Al-Thihli, Almundher Al-Maawali, Michael Schwake, Mariasavina Severino, Henry Houlden, Shunmoogum A. Patten, Juan S. Bonifacino, Kailash P. Bhatia, Dimitri Krainc
Niccolò E. Mencacci, Georgia Minakaki, Reza Maroofian, Raffaella De Pace, Adeline Paimboeuf, Tiago Branco Fonseca, Tatiana Abramova, Patrick Shannon, David Chitayat, Francesca Magrinelli, Wesley J. Peng, Diptaman Chatterjee, Sara H. Eldessouky, Julia Baptista, Tamas Marton, Julie Vogt, Juan Dario Ortigoza-Escobar, Loreto Martorell, Marta Gómez-Chiari, Ingrid M. Wentzensen, Erik-Jan Kamsteeg, Maha S. Zaki, Annarita Scardamaglia, Giovanni Zifarelli, Zuhair Nasser Al-Hassnan, Elka Miller, Shiri Shinar, Lova S. Matsa, Sri Hari Chandan Appikonda, Ghada A. Otaify, Khalid Al-Thihli, Almundher Al-Maawali, Michael Schwake, Mariasavina Severino, Henry Houlden, Shunmoogum A. Patten, Juan S. Bonifacino, Kailash P. Bhatia, Dimitri Krainc
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Research Article Cell biology Genetics Neuroscience

Pathogenic variants in BORCS5 cause a spectrum of neurodevelopmental and neurodegenerative disorders with lysosomal dysfunction

Abstract

BORCS5 encodes a subunit of the BLOC-One-Related Complex (BORC), which is known to promote anterograde movement and fusion of lysosomes. We identified 16 individuals from 9 families with bi-allelic BORCS5 variants, revealing a spectrum of neurodevelopmental and neurodegenerative phenotypes. Carriers of homozygous protein-truncating variants (PTVs), resulting in complete loss of BORCS5, presented with prenatally lethal arthrogryposis multiplex congenita, brain malformations, and neuropathological evidence of neuroaxonal dystrophy. Individuals with missense or splice-site variants presented differently, with microcephaly, developmental epileptic encephalopathy, optic atrophy, spasticity, and progressive movement disorders. In this group, brain MRI showed diffuse hypomyelination, corpus callosum abnormalities, and progressive global cerebral atrophy, consistent with neurodegeneration. Borcs5 KO in zebrafish resulted in microcephaly, motor deficits, and increased seizure susceptibility, mirroring the patients’ clinical presentation. At the cellular level, only BORCS5 PTVs, but not missense variants, led to perinuclear lysosomal clustering and impaired lysosomal axonal trafficking in induced pluripotent stem cell–derived forebrain neurons. However, PTVs and missense variants were associated with reduced lysosomal proteolysis and activity of lysosomal hydrolases glucocerebrosidase and cathepsin B, indicating lysosomal dysfunction. Our study reveals a role for BORCS5 in modulation of lysosomal function, in addition to its known role in lysosome movement and fusion, possibly underlying the diverse clinical manifestations in individuals with BORCS5-related disorders.

Authors

Niccolò E. Mencacci, Georgia Minakaki, Reza Maroofian, Raffaella De Pace, Adeline Paimboeuf, Tiago Branco Fonseca, Tatiana Abramova, Patrick Shannon, David Chitayat, Francesca Magrinelli, Wesley J. Peng, Diptaman Chatterjee, Sara H. Eldessouky, Julia Baptista, Tamas Marton, Julie Vogt, Juan Dario Ortigoza-Escobar, Loreto Martorell, Marta Gómez-Chiari, Ingrid M. Wentzensen, Erik-Jan Kamsteeg, Maha S. Zaki, Annarita Scardamaglia, Giovanni Zifarelli, Zuhair Nasser Al-Hassnan, Elka Miller, Shiri Shinar, Lova S. Matsa, Sri Hari Chandan Appikonda, Ghada A. Otaify, Khalid Al-Thihli, Almundher Al-Maawali, Michael Schwake, Mariasavina Severino, Henry Houlden, Shunmoogum A. Patten, Juan S. Bonifacino, Kailash P. Bhatia, Dimitri Krainc

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Figure 7

Lysosome-dispersal activity of patient-specific BORCS5 variants.

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Lysosome-dispersal activity of patient-specific BORCS5 variants. Increas...
Increased LysoTracker and decreased lysosomal enzyme activity in neurons with patient-specific BORCS5 variants. (A) Imaging of Lysotracker Red signal (red) in neurites of live iPSC-derived forebrain neurons (labeled with calcein, green) from WT, isogenic BORCS5-KO, or R95Q/L128fs patient iPSC lines. Scale bar: 10 μm. (B–D) Graphs show the mean ± SEM of 3 independent experiments. For vesicle number, 1-way ANOVA with Dunnett’s post-hoc test F(3,34) = 5.250 (P = 0.0044); for vesicle area, F(3,35) = 5.373 (P = 0.0038); for signal intensity, F(3,35) = 4.362 (P = 0.0104). (E) Imaging of Lysotracker Red endolysosomes (red) in the soma of iPSC-derived forebrain neurons from the indicated lines. Scale bar: 10 μm. (F) The graph shows the mean ± SEM of 3 independent experiments. For signal intensity, 1-way ANOVA with Dunnett’s post hoc test F(3,87) = 5.624 (P = 0.0014). (G) Fluorescence microscopy examination of LAMP1+ stained endolysosomes (green) and cathepsin B (CTSB) activity–derived fluorescent signal (red) in the soma of iPSC-derived forebrain neurons from the indicated lines. Scale bar: 10 μm. (H) The graph shows the mean ± SEM of 3 independent experiments. For CTSB activity soma, 1-way ANOVA with Dunnett’s post hoc test F(3,36) = 5.478 (P = 0.00333). Dots represent individual cells. Scale bar: 10 μm. (I) Fluorescence microscopy shows viable (calcein; red) day 21 iNeurons upon uptake of the lysosomal GCase substrate LysoFQ-GBA (green) and counterstained with DAPI. Scale bar: 50 μm. The lysosomal GCase activity–dependent fluorescent signal was quantified, and the graph shows the mean ± SEM of the relative intensity over mean WT within a specific experiment (n = 4 independent experiments). One-sample t test. **P = 0.0042.