Different gene expression profiles in iPSC-derived motor neurons from ALS8 patients with variable clinical courses suggest mitigating pathways for neurodegeneration

Abstract

Amyotrophic lateral sclerosis type 8 (ALS8) is an autosomal dominant form of ALS, which is caused by pathogenic variants in the VAPB gene. Here we investigated five ALS8 patients, classified as ‘severe’ and ‘mild’ from a gigantic Brazilian kindred, carrying the same VAPB mutation but displaying different clinical courses. Copy number variation and whole exome sequencing analyses in such individuals ruled out previously described genetic modifiers of pathogenicity. After deriving induced pluripotent stem cells (iPSCs) for each patient (N = 5) and controls (N = 3), motor neurons were differentiated, and high-throughput RNA-Seq gene expression measurements were performed. Functional cell death and oxidative metabolism assays were also carried out in patients’ iPSC-derived motor neurons. The degree of cell death and mitochondrial oxidative metabolism were similar in iPSC-derived motor neurons from mild patients and controls and were distinct from those of severe patients. Similar findings were obtained when RNA-Seq from such cells was performed. Overall, 43 genes were upregulated and 66 downregulated in the two mild ALS8 patients when compared with severe ALS8 individuals and controls. Interestingly, significantly enriched pathways found among differentially expressed genes, such as protein translation and protein targeting to the endoplasmic reticulum (ER), are known to be associated with neurodegenerative processes. Taken together, the mitigating mechanisms here presented appear to maintain motor neuron survival by keeping translational activity and protein targeting to the ER in such cells. As ALS8 physiopathology has been associated with proteostasis mechanisms in ER–mitochondria contact sites, such differentially expressed genes appear to relate to the bypass of VAPB deficiency.

Estudos genéticos e funcionais sobre os genes VAPB e VRK1 em duas famílias portadoras de Esclerose Lateral Amiotrófica

“…Such data suggested that unknown genetic modifiers might be playing a role in disease progression in these ALS8 patients (Oliveira et al, 2020).…”

“…Here we describe different aspects of ALS8 clinical variability, both in terms of clinical manifestations and in rate of disease progression. Then, we outline our recent work on ALS8 patients (Oliveira et al, 2020), in which we tried to address the molecular underpinnings of clinical progression variation in the patients we studied. We were able to rule out well-described genetic modifiers, such as EPHA4 and UNC13A, and potential copy number variation alterations.…”

“…In order to address this issue, we recently undertook the search for modifying genetic variants in five ALS8 patients from the same Brazilian family (Oliveira et al, 2020).…”

“…Although these individuals carry the same genetic mutation (VAPB P56S), they displayed different disease progression rates. We then hypothesized that genetic factors could be playing a role in such phenotypic heterogeneity (Oliveira et al, 2020). Three ALS8 patients classified as "severe" started the disease symptoms around their 50's.…”

“…Aiming to further evaluate the mechanism underlying their discordant clinical progressions, we reprogrammed erythroblasts from ALS8 severe and mild patients into induced pluripotent stem cells (iPSCs), differentiated them into motor neurons, and compared them to similar samples from three controls (Oliveira et al, 2020).…”