Biology subjects

Recinto, S. J.

Publications and source records attributed to Recinto, S. J..

4 recordsLinked to original sources

bioRxiv2024

Loss of the APP regulator RHBDL4 preserves memory in an Alzheimer's disease mouse model.

Characteristic cerebral pathological changes of Alzheimers disease (AD) such as glucose hypometabolism or the accumulation of cleavage products of the amyloid precursor protein (APP), known as A{beta} peptides, lead to sustained endoplasmic reticulum (ER) stress and neurodegeneration. To preserve ER homeostasis, cells activate their unfolded protein response (UPR). The rhomboid-like-protease 4 (RHBDL4) is an enzyme that participates in the UPR by targeting proteins for proteasomal degradation. We demonstrated previously that RHBLD4 cleaves APP in HEK293T cells, leading to decreased total APP and A{beta}. More recently, we showed that RHBDL4 processes APP in mouse primary mixed cortical cultures as well. Here, we aim to examine the physiological relevance of RHBDL4 in the brain. We first found that brain samples from AD patients and an AD mouse model (APPtg) showed increased RHBDL4 mRNA and protein expression. To determine the effects of RHBDL4s absence on APP physiology in vivo, we crossed APPtg mice to a RHBDL4 knockout (R4-/-) model. RHBDL4 deficiency in APPtg mice led to increased total cerebral APP and amyloidogenic processing when compared to APPtg controls. Contrary to expectations, as assessed by cognitive tests, RHBDL4 absence rescued cognition in 5-month-old female APPtg mice. Informed by unbiased RNAseq data, we demonstrated in vitro and in vivo that RHBDL4 absence leads to greater levels of active {beta}-catenin due to decreased proteasomal clearance. Decreased {beta}-catenin activity is known to underlie cognitive defects in APPtg mice and AD. Our work suggests that RHBDL4s increased expression in AD, in addition to regulating APP levels, leads to aberrant degradation of {beta}-catenin, contributing to cognitive impairment.

animal behavior and cognition↗

bioRxiv2024

Modeling gene-environment interactions in Parkinson's Disease: Helicobacter pylori infection of Pink1-/- mice induces CD8 T cell-dependent motor and cognitive dysfunction.

Parkinsons disease (PD) is a chronic neurodegenerative disorder characterized by progressive loss of motor function. Diagnosis occurs late: after motor symptom development downstream of the irreparable loss of a large proportion of the dopaminergic neurons in the substantia nigra of the brain. Understanding PD pathophysiology in its pre-motor prodromal phase is needed for earlier diagnosis and intervention. Genetic risk factors, environmental triggers, and dysregulated immunity have all been implicated in PD development. Here, we demonstrate in a mouse model deficient in the PD-associated gene Pink, that infection with the human PD-associated gastric bacterium Helicobacter pylori leads to development of motor and cognitive signs resembling prodromal features of PD. This was also associated with proliferation and activation of primary mitochondria-reactive CD8 T cells and infiltration of CD8 T cells into the brain. Development of the motor and cognitive phenotypes in the infected Pink1-/- mice was abrogated when CD8 T cells were depleted prior to infection. We anticipate that this new model, which integrates genetic PD susceptibility, a PD-relevant environmental trigger, and specific immune changes that are required for symptom development, will be a valuable tool for increasing our understanding of this complex disease.

immunology↗

bioRxiv2023

Eta-secretase-like processing of the amyloid precursor protein (APP) by RHBDL4

The amyloid precursor protein (APP) has been extensively studied with regards to its contribution to the pathology of Alzheimers disease. APP is an ubiquitously expressed type I transmembrane protein synthesized in the endoplasmic reticulum (ER) and translocated to the plasma membrane where it undergoes proteolytic cleavages by several identified proteases. Conversely to other known proteases, we previously elucidated human rhomboid protease RHBDL4 as a novel APP processing enzyme where several cleavages likely occur already in the ER. Interestingly, the pattern of RHBDL4-derived large APP C-terminal fragments resemble those generated by the {eta}-secretase or MT5-MMP, which was described to generate so called A{eta} fragments. The similarity in large APP C-terminal fragments between both proteases raised the question whether RHBDL4 may contribute to {eta}-secretase activity and A{eta}-like fragments. Here, we identified two cleavage sites of RHBDL4 in APP by mass spectrometry, which, intriguingly, lie in close proximity to the cleavage sites of MT5-MMP. Indeed, we observed that RHBDL4 generates A{eta}-like fragments in vitro without contributions of -, {beta}-, or {gamma}-secretases. Such A{eta}-like fragments are likely generated in the ER since RHBDL4-derived APP-C-terminal fragments do not reach the cell surface. Inherited, familial APP mutations appear to not affect this processing pathway. In RHBDL4 knockout mice, we observed increased cerebral full length APP levels in comparison to WT brains in support of RHBDL4 being a physiologically relevant protease for APP. Furthermore, we found secreted A{eta} fragments in dissociated mixed cortical cultures from wild type mice, however significantly less A{eta} fragments in cultures from RHBDL4 knockout mice. Our data underscores that RHBDL4 contributes to {eta}-secretease-like processing of APP and that RHBDL4 is a physiologically relevant protease for APP.

biochemistry↗

bioRxiv2023

CETP inhibitor evacetrapib enters mouse brain tissue

High levels of plasma cholesterol, especially high levels of low-density lipoprotein-cholesterol (LDL-C), have been associated with an increased risk of Alzheimers disease. The cholesteryl ester transfer protein (CETP) in plasma distributes cholesteryl esters between lipoproteins and increases LDL-C in plasma. Epidemiologically, decreased CETP activity has been associated with sustained cognitive performance during aging, longevity, and a lower risk of Alzheimers disease. Thus, pharmacological CETP inhibitors could potentially be repurposed for the treatment of Alzheimers disease as they are safe and effective at lowering CETP activity and LDL-C. While CETP is mostly expressed by the liver and secreted into the bloodstream, CETP is also expressed by astrocytes in the brain. It is therefore important to determine if CETP inhibitors can enter the brain. Here, we describe pharmacokinetic parameters of the CETP inhibitor evacetrapib in plasma, liver, and brain tissues in CETP transgenic mice. We show that evacetrapib crosses the blood-brain barrier and is detectable in brain tissue 0.5 h after a 40 mg/kg i.v. injection in a nonlinear function. We conclude that evacetrapib may prove to be a good candidate to treat CETP-mediated cholesterol dysregulation in Alzheimers disease.

pharmacology and toxicology↗