CK2 Phosphorylating SET Mediates The Neurofibrillary Pathology In Alzheimer’s Disease

Background:Casein kinase 2（CK2）is highly ubiquitous,evolutionarily conserved in eukaryotic cells.The CK2 holoenzyme is a serine/threonine protein kinase composed of two catalytic（α/α’）and two regulatory（β）subunits.CK2 has been implicated in numerous aspects of neural function,including neuronal survival,the regulation of some neurotransmitter receptors,circadian rhythm,and higher brain functions such as learning and memory.Overexpression of CK2 has been linked to several pathological conditions,ranging from cardiovascular pathologies and cancer progression to infectious diseases and neurodegeneration.Accumulated evidence demonstrates that as one of the first protein kinases identified in AD,CK2 immunoreactivity showed a significant 22%increase in neurofibrillary tangles（NFTs）-bearing hippocampal neurons with strong anti-tau immunolabeling,compared with those without NFTs.Compared to non-demented controls,CK2 level in the hippocampus and temporal cortex of AD patients is markedly increased.At the ultrastructural level anti-CK2 was immunolocalized to the paired helical filaments（PHF）of the tangle-bearing neurons,as well as to PHF in neuropil threads and some dystrophic neurites in plaques.These studies strongly indicate that CK2 hyper-activation may be involved in the pathology of AD.Being a key protein phosphatase in dephosphorylating tau,protein phosphatase-2A（PP2A）is compromised in the AD brains,while the level of its endogenous specific inhibitor 2(I₂^PP2A),also known as SET,is increased.SET is widely expressed in different tissues and localizes primarily in the nucleus,where it mainly protects histones from acetylation by histone acetyl transferases,modulates HuR mRNA binding,regulates G2/M transition via binding to p21CIP1,and acts as a transcription factor for P450c17 activation.In the AD brains,SET,which is located in nuclear,translocated to the cytoplasm.In the cytoplasm,SET co-localized with PP2A and hyperphosphorylated tau.Furthmore,hyperphosphorylated tau forms NFTs in the neurons.However,whether CK2 phosphorylates SET and regulates tau pathological phosphorylation in AD remains unclear.Objective:To investigate whether CK2 indeed phosphorylates SET in AD and mediates its inhibitory activity toward PP2A,resulting in tau hyperphosphorylation and neurofibrillary degeneration.Methods:We examined the activities of CK2 and SET Ser9 phosphorylation in neurons and animal models of AD.We also performed to determine the effect of CK2 or SET Ser9 phosphorylation mimetic mutant Overexpression in vivo and in vitro.At last,co-injection of non-phosphorylated SET S9A with CK2 were used to examine the link between CK2 and SET in AD mice.Results:1.CK2 activation is accompanied by SET hyperphosphorylation in an age-dependent manner in AD mice.2.AD-related CK2 activation induces SET phosphorylation and its cytoplasmic translocation.3.Overexpression of CK2 induces the cognitive deficits.4.Phosphorylation of SET induces PP2A inhibition and tau hyperphosphorylation.5.Overexpression of mimetic phosphorylated SET induces cognitive impairments.6.Phosphorylation of SET at Ser9 is required for CK2-induced tau pathology.Conclusion:CK2 phosphorylates Ser9 on SET leading to its cytoplasmic translocation and inhibition of PP2A resulting in tau phosphorylation and its neurofibrillary degeneration in AD.Selenizing Codonopsis pilosula Polysaccharide（s CPPs）is one of the major bioactive components of Selenizing Codonopsis pilosula which has been used in traditional Chinese medicine for thousands of years.However,the effects of s CPPs in AD remain poorly understood.We injected AAV-h Tau into mice,with daily intragastric administration of s CPPs for one month.The s CPPs-and control-treated mice were used to investigate the effects of s CPPs on AD-associated learning and memory impairment.Tau phosphorylation and numerous synaptic proteins were then investigated by using Western blots.s CPPs treatment significantly reduced hyperphosphorylation of tau at several AD-related phosphorylation sites.Meanwhile,protein phosphatase 2A,a major tau phosphatase was increased in vivo and in vitro.Daily intragastric administration of s CPPs abolished h Tau induced AD pathology and cognitive deficit.Our results demonstrate that treatment with s CPPs prevents AD-like pathological alterations and cognitive defectsn.These findings provide the first evidence supporting that Selenizing Codonopsis pilosula Polysaccharide might be a potential candidate compound for the prevention of cognitive decline and increased risk for AD and dementia.