An Insertion Within SIRPβ1 Shows a Dual Effect Over Alzheimer's Disease Cognitive Decline Altering the Microglial Response

Background

Microglial dysfunction plays a causative role in Alzheimer's disease (AD) pathogenesis. Here we focus on a germline insertion/deletion variant mapping SIRPβ1, a surface receptor that triggers amyloid-β(Aβ) phagocytosis via TYROBP.

Objective

To analyze the impact of this copy-number variant in SIRPβ1 expression and how it affects AD molecular etiology.

Methods

Copy-number variant proxy rs2209313 was evaluated in GERALD and GR@ACE longitudinal series. Hippocampal specimens of genotyped AD patients were also examined. SIRPβ1 isoform-specific phagocytosis assays were performed in HEK393T cells.

Results

The insertion alters the SIRPβ1 protein isoform landscape compromising its ability to bind oligomeric Aβ and its affinity for TYROBP. SIRPβ1 Dup/Dup patients with mild cognitive impairment show an increased cerebrospinal fluid t-Tau/Aβ ratio (p = 0.018) and a higher risk to develop AD (OR = 1.678, p = 0.018). MRIs showed that Dup/Dup patients exhibited a worse initial response to AD. At the moment of diagnosis, all patients showed equivalent Mini-Mental State Examination scores. However, AD patients with the duplication had less hippocampal degeneration (p < 0.001) and fewer white matter hyperintensities. In contrast, longitudinal studies indicate that patients bearing the duplication allele show a slower cognitive decline (p = 0.013). Transcriptional analysis also shows that the SIRPβ1 duplication allele correlates with higher TREM2 expression and an increased microglial activation.

Conclusions

The SIRPβ1 internal duplication has opposite effects over MCI-to-Dementia conversion risk and AD progression, affecting microglial response to Aβ. Given the pharmacological approaches focused on the TREM2-TYROBP axis, we believe that SIRPβ1 structural variant might be considered as a potential modulator of this causative pathway.

[Prognostic value of lipopolysaccharide binding protein and procalcitonin in patients with severe sepsis and septic shock admitted to intensive care]

AIMS

1) To assess the prognostic value of levels on admission and serial measurements of lipopolysaccharide binding protein (LBP) and procalcitonin (PCT) in relation to in-hospital mortality; and 2) to determine whether the addition of these parameters to severity scores (APACHE II and SOFA) is able to improve prognostic accuracy.

DESIGN

A single-center, prospective observational study was carried out.

SETTING

Intensive Care unit of a university hospital.

PATIENTS

One hundred severe sepsis and septic shock patients were included.

DATA COLLECTED

Demographic data, APACHE II and SOFA scores, PCT and LBP levels on admission and after 48 hours, and in-hospital mortality.

RESULTS

The best area under the curve for predicting in-hospital mortality corresponded to APACHE II on admission and SOFA after 48 h (AUC ROC: 0.75 for both). PCT and LBP levels on admission and LBP clearance were not statistically different between in-hospital survivors and non-survivors. Only PCT clearance was higher among in-hospital survivors than in non-survivors (AUC ROC: 0.66). The combination of severity scores and PCT clearance did not result in superior areas under the curve.

CONCLUSIONS

LBP and PCT levels on admission and LBP clearance showed no prognostic value in severe sepsis and septic shock patients. Only PCT clearance was predictive of in-hospital mortality. The prognostic accuracy was significantly better for APACHE on admission and SOFA after 48 h than for any of the analyzed biomarkers, and the addition of PCT clearance did not improve their prognostic value.