Harald Lund, Elin Gustafsson, Anne Svensson, Maria Nilsson, Margareta Berg, Dan Sunnemark, and Gabriel von Euler
Acta Neuropathol Commun. 2014; 2: 22
DOI: https://doi.org/10.1186/2051-5960-2-22
Abstract
Background:
The progression of Alzheimer’s disease (AD) is associated with an increase of phosphorylated tau in the brain. One of the earliest phosphorylated sites on tau is Ser262 that is preferentially phosphorylated by microtubule affinity regulating kinase (MARK), of which four isoforms exist. Herein we investigated the expression of MARK1-4 in the hippocampus of non-demented elderly (NDE) and AD cases.
Results:
In situ hybridization revealed a uniform, neuronal distribution of all four isoform mRNAs in NDE and AD. Immunohistochemical analyses using isoform-selective antibodies demonstrated that MARK4 in a phosphorylated form colocalizes with p-tau Ser262 in granulovacuolar degeneration bodies (GVDs) that progressively accumulate in AD. In contrast MARK4 is largely absent in the neuronal cytoplasm. MARK3 was localized to a subset of the GVD-containing neurons and also had a weak general cytoplasmic neuronal staining in both NDE and AD. These results suggest that in AD, phosphorylated MARK3 and MARK4 are sequestered and proteolysed in GVDs. MARK1 and MARK2 were absent in GVDs and exhibited relatively uniform neuronal expressions with no apparent differences between NDE and AD.
Conclusion:
We found that the phosphorylated and fragmented forms of MARK4 and to some extent MARK3 are present in GVDs in AD, and that this expression is highly correlated with phosphorylation of tau at Ser262. This may represent a cellular defense mechanism to remove activated MARK and p-tau Ser262 from the cytosol, thereby reducing the phosphorylating effect on tau Ser262 that appears to be a critical step for subsequent neurodegeneration.
Keywords:
Alzheimer’s disease, MARK, Phosphorylation, Granulovacuolar degeneration bodies, Tau
Understanding the molecular mechanisms behind Alzheimer's disease progression is crucial for developing effective treatments. A recent study sheds light on the role of MARK4 and MARK3 in the early phosphorylation of tau, a hallmark of the disease. The association of these proteins with granulovacuolar degeneration bodies, characteristic structures in Alzheimer's brains, highlights their potential as therapeutic targets. This research opens avenues for further exploration into targeted interventions to disrupt tau pathology. Interested in delving deeper into this groundbreaking study? Read here for comprehensive insights into the intricate interplay between MARK4, MARK3, and early tau phosphorylation in Alzheimer's disease progression.