Alzheimer's disease is a multifactorial disorder with a heterogeneous patient population. Comorbidities such as hypertension, hypercholesterolemia and diabetes are known contributors to the disease progression. Indeed, therapies targeting these disorders have been shown efficient in dementia prevention. However, their mechanistic contribution to Alzheimer's pathology and neurodegeneration has not been fully clarified. In the current study, we used CSF samples from a memory clinic cohort of 90 patients without diagnosed hypertension, hypercholesterolemia, or diabetes nor other neurodegenerative disorder, to investigate 13 molecular markers representing key mechanisms underlying Alzheimer's pathogenesis. Levels were compared between clinical groups of subjective cognitive decline, mild cognitive impairment, and Alzheimer's disease. Associations between markers and groups of markers were analyzed by linear regression. Two-step cluster analysis was used to determine patient clusters. Two key markers were further analyzed by immunofluorescence staining in hippocampus from control and AD individuals without hypertension, hypercholesterolemia nor diabetes. CSF angiotensinogen, thioredoxin-1, and interleukin-15 were the biomarkers with the most prominent associations with Alzheimer's pathology, synaptic and axonal damage. Synaptosomal-associated protein 25 kDa and neurofilament light chain were increased in mild cognitive impairment and Alzheimer cases. When we grouped biomarkers by biological function, we found that inflammatory and survival components were associated with Alzheimer's pathology, synaptic dysfunction and axonal damage. Moreover, a vascular/metabolic component was associated with synaptic dysfunction. In data-driven analysis, two patient clusters were identified; Older participants with increased CSF markers of oxidative stress, vascular pathology and neuroinflammation were assigned to cluster 1, that was also smaller and characterized by increased synaptic and axonal damage, compared to individuals in cluster 2. Clinical groups were evenly distributed between the clusters. Analysis of post-mortem hippocampal tissue, showed that, compared to controls, angiotensinogen staining was higher in Alzheimer's disease and was also found to co-localize with phosphorylated-tau. In a population free of common comorbidities, we could still find associations between Alzheimer's disease biomarkers and markers of pathways associated with increased risk for Alzheimer's disease (i.e., neuroinflammation, vascular function, oxidative stress and cholesterol homeostasis), suggesting that these pathways are contributing to Alzheimer's disease mechanisms even in absence of clinically diagnosed comorbidities. The identification of distinct biomarker-driven endophenotypes of cognitive disorder patients, further highlights the biological heterogeneity of Alzheimer's disease and the importance of developing tailored prevention and treatment strategies.
Background Cortisol, one of the most important mediators of stress in humans, is often found increased in Alzheimer’s disease (AD) patients and correlates with disease severity. Stress response and inflammation are two systems that are tightly associated to one another. Several lines of evidence suggest that cortisol can promote inflammation. However, less is known on the interaction of cortisol with neuroinflammation in the context of AD, and to the best of our knowledge there are no human studies that have systematically explored the association of these two systems in AD patients so far. The aim of this study was to investigate levels of cerebrospinal fluid (CSF) biomarkers of neuroinflammation and their relationship to salivary cortisol in a memory clinic cohort. Method A total of 108 memory clinic patients with subjective cognitive decline (SCI, n = 40), mild cognitive impairment (MCI, n = 39) and AD (n = 29), from the Karolinska University Hospital in Stockholm, Sweden, were included in this study. Salivary cortisol was collected at six timepoints during the day on two days, to quantify awakening cortisol, cortisol awakening response (CAR), bedtime cortisol and total cortisol. CSF levels of 37 neuroinflammation and cerebrovascular dysfunction biomarkers were determined by a multiplex immunoassay. Associations among cortisol and neuroinflammation markers were assessed by linear regression models adjusting for age and diagnosis. ANCOVA tests were used to compare biomarker levels between the diagnostic groups. Result Awakening cortisol was significantly elevated in the AD group compared to the SCI and MCI participants. Higher IP‐10 and placental growth factor (PlGF) levels were associated with decreased CAR independent of age and diagnosis. Thymus and activation‐regulated chemokine (TARC), CRP, intracellular adhesion molecule 1 (ICAM‐1) and vascular cell adhesion molecule 1 (VCAM‐1) levels were upregulated in MCI participants compared to SCI and AD. Conclusion We provide evidence that the HPA axis is altered in AD. Moreover, salivary cortisol is associated to neuroinflammation in an age and diagnosis independent manner. Finally, neuroinflammatory and vascular dysfunction regulators are increased in CSF during MCI stages followed by a drop in their levels in AD participants, presumably reflecting a more active role of neuroinflammation at an early state.
Although SRPKs were discovered nearly 30 years ago, our understanding of their mode of regulation is still limited. Regarded as constitutively active enzymes known to participate in diverse biological processes, their prominent mode of regulation mainly depends on their intracellular localization. Molecular chaperones associate with a large internal spacer sequence that separates the bipartite kinase catalytic core and modulates the kinases’ partitioning between the cytoplasm and nucleus. Besides molecular chaperones that function as anchoring proteins, a few other proteins were shown to interact directly with SRPK1, the most-studied member of SRPKs, and alter its activity. In this study, we identified TAF15, which has been involved in transcription initiation, splicing, DNA repair, and RNA maturation, as a novel SRPK1-interacting protein. The C-terminal RGG domain of TAF15 was able to associate with SRPK1 and downregulate its activity. Furthermore, overexpression of this domain partially relocalized SRPK1 to the nucleus and resulted in hypophosphorylation of SR proteins, inhibition of splicing of a reporter minigene, and inhibition of Lamin B receptor phosphorylation. We further demonstrated that peptides comprising the RGG repeats of nucleolin, HNRPU, and HNRNPA2B1, were also able to inhibit SRPK1 activity, suggesting that negative regulation of SRPK1 activity might be a key biochemical property of RGG motif-containing proteins.
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