Circulating apoptotic factors in patients with acute cerebral infarction

Induced pluripotent stem cell models as a tool to investigate and test fluid biomarkers in Alzheimer's disease and frontotemporal dementia

Neurodegenerative diseases are increasing in prevalence and comprise a large socioeconomic burden on patients and their caretakers. The need for effective therapies and avenues for disease prevention and monitoring is of paramount importance. Fluid biomarkers for neurodegenerative diseases have gained a variety of uses, including informing participant selection for clinical trials, lending confidence to clinical diagnosis and disease staging, determining prognosis, and monitoring therapeutic response. Their role is expected to grow as disease-modifying therapies start to be available to a broader range of patients and as prevention strategies become established. Many of the underlying molecular mechanisms of currently used biomarkers are incompletely understood. Animal models and in vitro systems using cell lines have been extensively employed but face important translatability limitations. Induced pluripotent stem cell (iPSC) technology, where a theoretically unlimited range of cell types can be reprogrammed from peripheral cells sampled from patients or healthy individuals, has gained prominence over the last decade. It is a promising avenue to study physiological and pathological biomarker function and response to experimental therapeutics. Such systems are amenable to high-throughput drug screening or multiomics readouts such as transcriptomics, lipidomics, and proteomics for biomarker discovery, investigation, and validation. The present review describes the current state of biomarkers in the clinical context of neurodegenerative diseases, with a focus on Alzheimer's disease and frontotemporal dementia. We include a discussion of how iPSC models have been used to investigate and test biomarkers such as amyloid-β, phosphorylated tau, neurofilament light chain or complement proteins, and even nominate novel biomarkers. We discuss the limitations of current iPSC methods, mentioning alternatives such as coculture systems and three-dimensional organoids which address some of these concerns. Finally, we propose exciting prospects for stem cell transplantation paradigms using animal models as a preclinical tool to study biomarkers in the in vivo context.

Hyperglycaemia-associated Caspase-3 predicts diabetes and coronary artery disease events

BACKGROUND

Apoptosis is central in both diabetes and atherosclerosis, linked to pancreatic beta cell death and plaque progression. Circulating Caspase-3 has also been associated with diabetes and coronary calcium score. Here, we explored if soluble Caspase-3 (sCaspase-3) is associated with cardio-metabolic risk factors and predicts incidence of diabetes and coronary artery disease (CAD).

METHODS

Clinical data and plasma from 4637 individuals from the Malmö Diet and Cancer cohort were studied. Plasma sCaspase-3 was measured by a Proximity Extension Assay. National registers were used to identify diabetes and CAD events during follow-up. Type 2 diabetes risk variants and expression quantitative trait loci (eQTL) for sCaspase-3 were retrieved from the DIAGRAM consortium and the Genotype-Tissue Expression project.

RESULTS

HbA1c was the factor with the strongest association with sCaspase-3 (r = 0.18, P = 1.3x10^-36 ). During follow-up 666 individuals developed diabetes and 648 individuals suffered from CAD. Increasing sCaspase-3 was associated with a higher risk of developing diabetes (hazard ratio (HR) 1.18 per 1unit; P = 7 × 10^-5 ) and CAD (HR 1.2 per 1 unit, P = 1 × 10^-4 ) during follow-up. A genetic variant rs60780116, located upstream of CASP3, showed strong association with type 2 diabetes (OR 1.06, 95%CI 1.04-1.07, P = 8.4 × 10^-11 ). An eQTL was identified between this variant and gene expression of CASP3, where the allele positively correlated with type 2 diabetes was associated with increased CASP3 expression in blood.

CONCLUSIONS

The present study provides evidence for plasma sCaspase-3 as a marker of cardio-metabolic risk factors and as a predictor of future diabetes and CAD in a cohort without cardiovascular disease or diabetes at baseline.

Exoenzyme Y induces extracellular active caspase-7 accumulation independent from apoptosis: modulation of transmissible cytotoxicity

Caspase-3 and -7 are executioner caspases whose enzymatic activity is necessary to complete apoptotic cell death. Here, we questioned whether endothelial cell infection leads to caspase-3/7-mediated cell death. Pulmonary microvascular endothelial cells (PMVECs) were infected with Pseudomonas aeruginosa (PA103). PA103 caused cell swelling with a granular appearance, paralleled by intracellular caspase-3/7 activation and cell death. In contrast, PMVEC infection with ExoY⁺ (PA103 ΔexoUexoT::Tc pUCPexoY) caused cell rounding, but it did not activate intracellular caspase-3/7 and it did not cause cell death. However, ExoY⁺ led to a time-dependent accumulation of active caspase-7, but not caspase-3, in the supernatant, independent of apoptosis. To study the function of extracellular caspase-7, caspase-7- and caspase-3-deficient PMVECs were generated using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology. Caspase-7 activity was significantly reduced in supernatants from infected caspase-7-deficient cells but was unchanged in supernatants from infected caspase-3 deficient cells, indicating an uncoupling in the mechanism of activation of these two enzymes. Because ExoY⁺ leads to the release of heat stable amyloid cytotoxins that are responsible for transmissible cytotoxicity, we next questioned whether caspase-7 contributes to the severity of this process. Supernatants obtained from infected caspase-7-deficient cells displayed significantly reduced transmissible cytotoxicity when compared with supernatants from infected wild-type controls, illustrating an essential role for caspase-7 in promoting the potency of transmissible cytotoxicity. Thus, we report a mechanism whereby ExoY⁺ infection induces active caspase-7 accumulation in the extracellular space, independent of both caspase-3 and cell death, where it modulates ExoY⁺-induced transmissible cytotoxicity.

Association of genetic polymorphisms in CASP7 with risk of ischaemic stroke

Caspase 7 (CASP7) is located on chromosome 10q25.3 that has been identified to be a susceptibility locus of ischaemic stroke (IS) by genome-wide association study. Elevated CASP7 was observed in IS, acting as a key apoptotic mediator in the development of IS. The aim of this study was to investigate the association between genetic polymorphisms in CASP7 and risk of IS. The CASP7 polymorphisms were genotyped using a TaqMan allelic discrimination assay. The expression levels of CASP7 mRNA were examined using quantitative polymerase chain reaction and luciferase activity was analyzed using the Dual Luciferase reporter assay. The rs12415607 in the promoter of CASP7 was associated with a reduced risk of IS (AA vs. CC: adjusted OR = 0.55, 95% CI: 0.38-0.80, P = 0.002; CA/AA vs. CC: adjusted OR = 0.70, 95% CI: 0.54-0.91, P = 0.007; AA vs. CC/CA: adjusted OR = 0.64, 95% CI: 0.46-0.90, P = 0.01; A vs. C: adjusted OR = 0.74, 95% CI: 0.62-0.89, P = 0.001). Moreover, the rs12415607 AA genotype carriers exhibited lower levels of CASP7 mRNA and the rs12415607 A allele decreased the promoter activity. These findings indicate that the rs12415607 A allele induces lower levels of transcriptional activity and CASP7 mRNA, and thus is associated with a reduced risk of IS.

Serum Caspase-3 Levels and Early Mortality of Patients with Malignant Middle Cerebral Artery Infarction

PURPOSE

Circulating caspase-3 levels at 24 h of ischemic stroke were found to be associated with poorer functional neurological outcome in a previous study. The aim of this study was to determine whether there is an association between serum caspase-3 levels and early mortality in patients with malignant middle cerebral artery infarction (MMCAI).

METHODS

We included patients with MMCAI defined as computer tomography showing ischemic changes in more than 50% of the middle cerebral artery territory and Glasgow Coma Scale ≤ 8. Serum caspase-3 levels at days 1, 4, and 8 of MMCAI were determined.

RESULTS

Non-surviving MMCAI (n = 34) showed higher serum caspase-3 levels at days 1 (p < 0.001), 4 (p = 0.001), and 8 (p = 0.01) than surviving patients (n = 34). We found that the area under the curve of serum caspase-3 levels for prediction of mortality at 30 days was 88% (95% CI = 78-95%; p < 0.001). Multiple logistic regression showed that serum caspase-3 levels were associated with 30-day mortality (OR = 51.25; 95% CI = 8.30-316.31; p < 0.001).

CONCLUSIONS

The novel and more important findings of our study were that high serum caspase-3 levels were associated with mortality in MMCAI patients.

Prospective clinical biomarkers of caspase-mediated apoptosis associated with neuronal and neurovascular damage following stroke and other severe brain injuries: Implications for chronic neurodegeneration

Acute brain injuries, including ischemic and hemorrhagic stroke, as well as traumatic brain injury (TBI), are major worldwide health concerns with very limited options for effective diagnosis and treatment. Stroke and TBI pose an increased risk for the development of chronic neurodegenerative diseases, notably chronic traumatic encephalopathy, Alzheimer's disease, and Parkinson's disease. The existence of premorbid neurodegenerative diseases can exacerbate the severity and prognosis of acute brain injuries. Apoptosis involving caspase-3 is one of the most common mechanisms involved in the etiopathology of both acute and chronic neurological and neurodegenerative diseases, suggesting a relationship between these disorders. Over the past two decades, several clinical biomarkers of apoptosis have been identified in cerebrospinal fluid and peripheral blood following ischemic stroke, intracerebral and subarachnoid hemorrhage, and TBI. These biomarkers include selected caspases, notably caspase-3 and its specific cleavage products such as caspase-cleaved cytokeratin-18, caspase-cleaved tau, and a caspase-specific 120 kDa αII-spectrin breakdown product. The levels of these biomarkers might be a valuable tool for the identification of pathological pathways such as apoptosis and inflammation involved in injury progression, assessment of injury severity, and prediction of clinical outcomes. This review focuses on clinical studies involving biomarkers of caspase-3-mediated pathways, following stroke and TBI. The review further examines their prospective diagnostic utility, as well as clinical utility for improved personalized treatment of stroke and TBI patients and the development of prophylactic treatment chronic neurodegenerative disease.

Chronic cerebral hypoperfusion in rats causes proteasome dysfunction and aggregation of ubiquitinated proteins

The deposition of abnormal protein aggregates is a feature of several neurodegenerative diseases. We have employed a rat model to investigate whether chronic cerebral hypoperfusion (CCH) induces proteasome dysfunction and the accumulation of ubiquitinated proteins and aggregates in the CNS. Protein aggregation was analyzed by ethanolic phosphotungstic acid (EPTA) electron microscopy (EM), immunogold EM, laser-scanning confocal microscopy, and Western blotting. Proteasome peptidase activity was studied by peptidase activity assays. EPTA EM and immunogold EM revealed that CCH led to the accumulation of protein aggregates in rat hippocampal CA1 neurons. High-resolution confocal microscopy demonstrated the presence of ubiquitin-positive protein aggregates surrounding nuclei and along dendrites. Western blotting revealed that levels of free ubiquitin were significantly reduced and that levels of ubiquitinated proteins were markedly increased in the hippocampus of CCH rats. Direct activity measurements revealed that proteasome peptidase activity in the hippocampal region of rats was decreased after CCH induction. These data suggest that reduced proteasome activity following CCH could impair the removal of abnormally folded proteins via the ubiquitin-proteasome pathway, leading to the accumulation of potentially toxic protein aggregates that could contribute to neurodegeneration.