Cytoskeletal changes during development and aging in the cortex of neurofilament light protein knockout mice

• Published in: Journal of comparative neurology (1911) Vol. 521; no. 8; pp. 1817 - 1827
• Main Authors: Liu, Yao, Staal, Jerome A., Canty, Alison J., Kirkcaldie, Matthew T. K., King, Anna E., Bibari, Olivier, Mitew, Stan T., Dickson, Tracey C., Vickers, James C.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.06.2013; Wiley Subscription Services, Inc
• Subjects: Aging; Aging - metabolism; Analysis of Variance; Animals; Cerebral Cortex - cytology; Cerebral Cortex - growth & development; Cerebral Cortex - metabolism; cytoskeletal protein; Cytoskeletal Proteins - metabolism; Cytoskeleton - metabolism; Gene Expression Regulation, Developmental - genetics; interneuron; Mice; Mice, Inbred C57BL; Mice, Knockout; Nerve Tissue Proteins - metabolism; neurofilament; Neurofilament Proteins - deficiency; Neurofilament Proteins - genetics; Neurons - cytology; pyramidal neurons
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23261

The neurofilament light (NFL) subunit is considered as an obligate subunit polymer for neuronal intermediate filaments comprising the neurofilament (NF) triplet proteins. We examined cytoskeletal protein levels in the cerebral cortex of NFL knockout (KO) mice at postnatal day 4 (P4), 5 months, and 12 months of age compared with age‐matched wild‐type (WT) mice of a similar genetic background (C57BL/6). The absence of NFL protein resulted in a significant reduction of phosphorylated and dephosphorylated NFs (NF‐P, NF‐DP), the medium NF subunit (NFM), and the intermediate filament α‐internexin (INT) at P4. At 5 months, NF‐DP, NFM, and INT remained significantly lower in knockouts. At 12 months, NF‐P was again significantly decreased, and INT significantly increased, in KOs compared with wild type. In addition, protein levels of class III neuron‐specific β‐tubulin and microtubule‐associated protein 2 were significantly increased in NFL KO mice at P4, 5 months, and 12 months, whereas β‐actin levels were significantly decreased at P4. Immunocytochemical studies demonstrated that NF‐DP accumulated abnormally in the perikarya of cortical neurons by 5 months of age in NFL KO mice. Neurons that lacked NF triplet proteins, such as calretinin‐immunolabeled nonpyramidal cells, showed no alterations in density or cytoarchitectural distribution in NFL KO mice at 5 months relative to WT mice, although calretinin protein levels were decreased significantly after 12 months in NFL KO mice. These findings suggest that a lack of NFL protein alters the expression of cytoskeletal proteins and disrupts other NF subunits, causing intracellular aggregation but not gross structural changes in cortical neurons or cytoarchitecture. The data also indicate that changes in expression of other cytoskeletal proteins may compensate for decreased NFs. J. Comp. Neurol. 521:1817–1827, 2013. © 2012 Wiley Periodicals, Inc. Neurofilament light (NFL) is an obligate subunit for neurofilament triplet intermediate filaments. We examined the effect of NFL knockout on the expression of cytoskeletal proteins in the cortex at 4 days, 5 months, and 12 months postnatally. Deleting NFL alters the expression of intermediate filament proteins, including α‐internexin, and disrupts neurofilament assembly and transport, causing intracellular aggregation but no gross structural changes in cytoarchitecture. In addition, changes in expression of other cytoskeletal proteins may compensate for altered neurofilament expression.