Nuclear lamina invaginations are not a pathological feature of C9orf72 ALS/FTD

Abstract

The most common genetic cause of familial and sporadic amyotrophic lateral sclerosis (ALS) is a GGGGCC hexanucleotide repeat expansion (HRE) in the C9orf72 gene. While direct molecular hallmarks of the C9orf72 HRE (repeat RNA foci, dipeptide repeat protein pathology) are well characterized, the mechanisms by which the C9orf72 HRE causes ALS and the related neurodegenerative disease frontotemporal dementia (FTD) remain poorly understood. Recently, alterations to the nuclear pore complex and nucleocytoplasmic transport have been accepted as a prominent pathomechanism underlying C9orf72 ALS/FTD. However, global disruptions to nuclear morphology and the nuclear lamina itself remain controversial. Here, we use a large number of induced pluripotent stem cell derived spinal neurons and postmortem human motor cortex sections to thoroughly examine nuclear morphology and nuclear lamina disruptions with light microscopy. In contrast to previous studies in artificial overexpression model systems, endogenous levels of the C9orf72 HRE do not increase the frequency of nuclear lamina invaginations. In addition, the C9orf72 HRE has no impact on overall nuclear shape and size. Notably, the frequency of nuclear Lamin B1 invaginations increases with cellular aging, independent of the C9orf72 HRE. Together, our data suggest that nuclear morphology is unaltered in C9orf72 ALS/FTD.

Nuclear morphology predicts cell survival to cisplatin chemotherapy

“…Nuclear circularity is a representative 2D feature that allows for the evaluation of morphological abnormalities and it is used as a diagnostic parameter by pathologists 57,59,128,129 . Sphericity is a 3D version of circularity that may provide identical diagnostic potential or even better specificity due to the additional dimensional information 59,130,131 . Treated cells exhibited a decreasing nuclear volume as a function of recovery time, with the lowest sphericity values occurring in the population of cells in the PACC state at day 15.…”

The Role of Nucleocytoplasmic Transport Defects in Amyotrophic Lateral Sclerosis

“…Second, the findings are not always conclusive. For example, abnormal lamin-β staining was observed in fibroblasts derived from mutant C9orf72 patients [90], but not in mutant C9orf72 patient-derived induced neurons [92], spinal neurons derived from induced pluripotent stem cells (iPSCs) [97] or postmortem material from mutant C9orf72 patients [97]. Moreover, the aberrant localizations of nucleocytoplasmic transport proteins are not observed in all studies [87,88,90].…”

Neuronal intranuclear inclusion disease: Polyglycine protein is the culprit

“…An intriguing finding in NIID postmortem tissue is that, relative to controls, there is a consistent increase in nuclear size of pontine neurons harboring nuclear inclusions and a corresponding decrease in nuclear size of adjacent neurons (Uchihara et al, 2003). An increase in overall nuclear shape and size is not found in C9orf72 ALS/FTD, but alterations in nuclear pore complex and nucleocytoplasmic transport are important mechanisms underlying this disease and other DNA expansion disorders (Coyne and Rothstein, 2021). In a related disease, fragile-X-associated tremor/ ataxia syndrome (FXTAS), the FMR polyG protein interacts with the nuclear lamina protein LAP2b, leading to disorganization of the nuclear lamina architecture in neurons derived from FXTAS patient induced pluripotent stem cells (iPSCs) (Sellier et al, 2017).…”