No abstract

Fibrinogen (Fg)-containing plaques are associated with memory loss during various inflammatory neurodegenerative diseases such as Alzheimer’s disease, multiple sclerosis, stroke, and traumatic brain injury. However, mechanisms of its action in neurovascular unit are not clear. As Fg is a high molecular weight blood protein and cannot translocate far from the vessel after extravasation, we hypothesized that it may interact with astrocytes first causing their activation. Cultured mouse cortical astrocytes were treated with Fg in the presence or absence of function-blocking anti-mouse ICAM-1 antibody, or with medium alone (control). Expressions of intercellular adhesion molecules 1 (ICAM-1) and tyrosine receptor kinase B (TrkB) as markers of astrocyte activation, and phosphorylation of TrkB (pTrkB) were assessed. Fg dose-dependently increased activation of astrocytes defined by their shape change, retraction of processes, and enhanced expressions ICAM-1 and TrkB, and increased pTrkB. Blocking of ICAM-1 function ameliorated these Fg effects. Data suggest that Fg interacts with astrocytes causing overexpression of ICAM-1 and TrkB, and TrkB phosphorylation, and thus, astrocyte activation. Since TrkB is known to be involved in neurodegeneration, interaction of Fg with astrocytes and the resultant activation of TrkB can be a possible mechanism involved in memory reduction, which were observed in previous studies and were associated with formation of complexes of Fg deposited in extravascular space with proteins such as Amyloid beta or prion, the proteins involved in development of dementia.

Traumatic brain injury (TBI) is one of the most common neurological disorders causing memory reduction, particularly short-term memory (STM). We showed that during TBI-induced inflammation, increased blood content of fibrinogen (Fg) enhanced vascular protein transcytosis and deposition of extravasated Fg in vasculo-astrocyte interfaces. In addition, we found that deposition of cellular prion protein (PrPC) was also increased in the vasculo-astrocyte endfeet interface. However, association of Fg and PrPC was not confirmed. Presently, we aimed to define whether Fg can associate with PrPC on astrocytes and cause their activation. Cultured mouse brain astrocytes MBA were treated with medium alone (control), Fg (2 mg/ml or 4 mg/ml), 4 mg/ml of Fg in the presence of a function-blocking anti-PrPC peptide or anti-mouse IgG, function-blocking anti-PrPC peptide, or anti-mouse IgG alone. After treatment, either cell lysates were collected and analyzed via Western blot or co-immunoprecipitation was performed, or astrocytes were fixed and their activation was assessed with immunohistochemistry. Results showed that Fg dose-dependently activated astrocytes, increased expressions of PrPC and tyrosine (tropomyosin) receptor kinase B (TrkB), and PrP gene. Blocking the function of PrPC reduced these effects. Co-immunoprecipitation demonstrated Fg and PrPC association. Since it is known that prion protein has a greater effect on memory reduction than amyloid beta, and that activation of TrkB is involved in neurodegeneration, our findings confirming the possible formation of Fg-PrPC and Fg-induced overexpression of TrkB on astrocytes suggest a possible triggering mechanism for STM reduction that was seen previously during mild-to-moderate TBI.

Traumatic brain injury (TBI) is an increasing health problem. It is a complex, progressive disease that consists of many factors affecting memory. Studies have shown that increased blood‐brain barrier (BBB) permeability initiates pathological changes in neuro‐vascular network but the role of cerebrovascular dysfunction and its mediated mechanisms associated with memory reduction during TBI are still not well understood. Changes in BBB, inflammation, extravasation of blood plasma components, activation of neuroglia lead to neurodegeneration. Extravasated proteins such as amyloid‐beta, fibrinogen, and cellular prion protein may form degradation resistant complexes that can lead to neuronal dysfunction and degeneration. They also have the ability to activate astrocytes, and thus, can be involved in memory impairment. Understanding the triggering mechanisms and the places they originate in vasculature or in extravascular tissue may help to identify potential therapeutic targets to ameliorate memory reduction during TBI. The goal of this review is to discuss conceptual mechanisms that lead to short‐term memory reduction during non‐severe TBI considering distinction between vascular and non‐vascular effects on neurons. Some aspects of these mechanisms need to be confirmed further. Therefore, we hope that the discussion presented bellow may lead to experiments that may clarify the triggering mechanisms of memory reduction after head trauma.

Background Type 2 diabetes (T2D) is the leading non-communicable disease worldwide and is associated with several microvascular and macrovascular complications. Individuals with T2D are more prone to acquiring selected types of infections and are more susceptible to complications due to these infections. This study aimed to evaluate the relationship between T2D and COVID-19 in the community setting. Methods This was a single-center retrospective analysis that included 147 adult patients with laboratory-confirmed COVID-19 admitted to a community hospital. Demographics, medical history, symptoms and signs, laboratory findings, complications during the hospital course, and treatments were collected and analyzed. The Kaplan-Meier method was used to describe the probability of intubation in patients with T2D as compared with patients without T2D. The hazard ratio for intubation in the survival analysis was estimated using a bivariable Cox proportional-hazards model. Results Of 147 patients, 73 (49.7%) had a history of T2D. Patients with T2D had higher requirement of ICU admission (31.5% vs 12.2%; p=.004), higher incidence of ARDS (35.6% vs 16.2%, p=.007), higher rates of intubation (32.9% vs 12.2%, p=0.003), and higher use neuromuscular blocking agents (23.3% vs 9.5%, p=.02). In the survival analysis at 28 days of follow-up, patients with T2D showed an increased hazard for intubation (HR 3.00; 95% CI, 1.39 to 6.46). Conclusion In our patient population, patients with COVID-19 and T2D showed significantly higher ARDS incidence and intubation rates. The survival analysis also showed that after 28 days of follow-up, patients with T2D presented an increased risk for shorter time to intubation.