Chronic neurodegeneration induces type I interferon synthesis via STING, shaping microglial phenotype and accelerating disease progression.

Type I interferons (IFN-I) are the principal antiviral molecules of the innate immune system and can be made by most cell types, including central nervous system cells. IFN-I has been implicated in neuroinflammation during neurodegeneration, but its mechanism of induction and its consequences remain unclear. In the current study, we assessed expression of IFN-I in murine prion disease (ME7) and examined the contribution of the IFN-I receptor IFNAR1 to disease progression. The data indicate a robust IFNß response, specifically in microglia, with evidence of IFN-dependent genes in both microglia and astrocytes. This IFN-I response was absent in stimulator of interferon genes (STING-/- ) mice. Microglia showed increased numbers and activated morphology independent of genotype, but transcriptional signatures indicated an IFNAR1-dependent neuroinflammatory phenotype. Isolation of microglia and astrocytes demonstrated disease-associated microglial induction of Tnfα, Tgfb1, and of phagolysosomal system transcripts including those for cathepsins, Cd68, C1qa, C3, and Trem2, which were diminished in IFNAR1 and STING deficient mice. Microglial increases in activated cathepsin D, and CD68 were significantly reduced in IFNAR1-/- mice, particularly in white matter, and increases in COX-1 expression, and prostaglandin synthesis were significantly mitigated. Disease progressed more slowly in IFNAR1-/- mice, with diminished synaptic and neuronal loss and delayed onset of neurological signs and death but without effect on proteinase K-resistant PrP levels. Therefore, STING-dependent IFN-I influences microglial phenotype and influences neurodegenerative progression despite occurring secondary to initial degenerative changes. These data expand our mechanistic understanding of IFN-I induction and its impact on microglial function during chronic neurodegeneration.

DNA sensors are expressed in astrocytes and microglia in vitro and are upregulated during gliosis in neurodegenerative disease.

The detection of nucleic acids by the innate immune system is an essential host response during viral infection. In recent years, a number of immune sensors capable of recognizing cytosolic DNA have been identified and include the PYHIN family members AIM2, IFI16, and p204 as well as the enzyme, cGAS. Activation of these receptors leads to the induction of antiviral genes including Type-1 interferons and chemokines such as CCL5. We have carried out extensive expression profiling of these DNA sensors and other members of the PYHIN family in highly purified primary astrocytes and microglia and have demonstrated that both cell types express the majority of these proteins at the mRNA level. In microglia, several family members are highly upregulated in response to IFN-ß treatment while both cell types induce robust proinflammatory and antiviral cytokine production (e.g., IL-6, CCL5, IFN-ß) in the presence of immune stimulatory DNA and RNA. The production of IL-6 is partially dependent on the interferon receptor as is IFN-ß itself. Furthermore, we have found that p204 and AIM2 are upregulated in a Type I IFN dependent fashion in vivo, in a murine model of chronic neurodegeneration. Given the propensity of inflammatory responses to cause neuronal damage, increased expression and activation of these receptors, not only during viral infection but also during sterile inflammatory responses, has the potential to exacerbate existing neuroinflammation leading to further damage and impaired neurogenesis.

Towards an understanding of why undergraduate teaching about delirium does not guarantee gold-standard practice--results from a UK national survey.

BACKGROUND: delirium is common and serious, yet frequently missed by medical staff. It is known that delirium is widely taught and examined in UK medical schools; however, what is taught, and how such teaching is delivered, remains unknown. The primary aim of this study was to determine the content of UK undergraduate medical education about delirium and establish how it is delivered. A secondary aim was to highlight and share examples of gold-standard teaching on delirium. METHODS: all UK undergraduate medical schools were invited to complete a survey. Schools were asked to describe how delirium was taught and to provide delirium-related learning outcomes. Learning outcomes were mapped to the three overarching themes outlined in Tomorrow's Doctors (knowledge, skills and attitudes). RESULTS: 24/31 schools (77%) provided responses. In line with previous work, delirium was widely taught and examined. 18/24 schools reported at least one learning outcome that mapped to the knowledge domain, 19/24 for the skills domain and 2/24 for the attitudes domain. 4/24 evaluated the impact of sessions and 3/24 involved patients and the public in teaching. 13/24 schools were confident that exposure to delirium was guaranteed. Innovative teaching methods were reported by a number of schools; weblinks to examples are provided. DISCUSSION: there was widespread failure to address attitudes on delirium within teaching, to evaluate the impact of sessions, to involve patients and the public in teaching and to guarantee exposure to delirium. Future teaching interventions should be directed at attitudinal outcomes, using a synthesis of clinical experience with multidisciplinary interaction and supportive technologies.

Prior pathology in the basal forebrain cholinergic system predisposes to inflammation-induced working memory deficits: reconciling inflammatory and cholinergic hypotheses of delirium.

Delirium is a profound, acute confusional state that leads to long-term cognitive decline. Increased anticholinergic medications and prior dementia, in which basal forebrain cholinergic degeneration is a prominent feature, both predict delirium. Thus, cholinergic hypoactivity is thought to be important in cognitive dysfunction during delirium, and acute systemic inflammation is a major trigger for this dysfunction. Here, we hypothesize that decreased cholinergic function confers increased susceptibility to acute inflammation-induced cognitive deficits. We used the murine-p75-saporin immunotoxin (mu-p75-sap) to induce selective lesions of the basal forebrain cholinergic system in mice, mimicking early dementia-associated cholinergic loss, and superimposed systemic inflammation using low-dose bacterial lipopolysaccharide (LPS). Intracerebroventricular injection of mu-p75-sap produced depletion of cholinergic neurons in the basal forebrain and decreased innervation of the hippocampus, but left performance on hippocampal-dependent reference and working memory tasks relatively intact. However, systemic LPS (100 µg/kg) induced acute and transient working memory deficits in lesioned animals without effect in unlesioned controls. CNS inflammatory responses were similar in normal and lesioned animals and the acetylcholinesterase inhibitor, donepezil (1 mg/kg), protected against the acute cognitive deficits in this cholinergic-dependent task. Thus, cholinergic depletion predisposes to development of acute cognitive deficits upon subsequent systemic inflammatory insult. These data provide a useful model for examining interactions between acute systemic inflammation and chronic cholinergic hypofunction in delirium and have implications for the recent trial of rivastigmine in sepsis-associated delirium.

Microglia in the degenerating brain are capable of phagocytosis of beads and of apoptotic cells, but do not efficiently remove PrPSc, even upon LPS stimulation.

Despite the phagocytic machinery available to microglia the aberrant amyloid proteins produced during Alzheimer's and prion disease, amyloid-ß and PrP(Sc), are inefficiently cleared. We have shown that microglia in the ME7 model of prion disease show morphological evidence of activation, synthesize low levels of pro-inflammatory cytokines and are primed to produce exaggerated responses to subsequent inflammatory challenges. Whether these microglia engage in significant phagocytic activity in the disease per se, or upon subsequent inflammatory challenge is not clear. In the present study we show transcriptional activation of a large number of scavenger receptors (SRs), matrix metalloproteinases (MMPs), oxidative enzymes, and cathepsins in ME7 animals. Hippocampally-injected inert latex beads (6 µm) are efficiently phagocytosed by microglia of ME7 prion-diseased animals, but not by microglia in normal animals. Stimulation of ME7 animals with systemic bacterial endotoxin (lipopolysaccharide, LPS) induced further increases in SR-A2, MMP3, and urokinase plasminogen activator receptor (uPAR) but decreased, or did not alter, transcription of most phagocytosis-related genes examined and did not enhance clearance of deposited PrP(Sc). Furthermore, intracerebral injection with LPS (0.5 µg) induced marked microglial production of IL-1ß, robust cellular infiltration and marked apoptosis but also did not induce further clearance of PrP(Sc). These data indicate that microglia in the prion-diseased brain are capable of phagocytosis per se, but show limited efficacy in removing PrP(Sc) even upon marked escalation of CNS inflammation. Furthermore, microglia/macrophages remain IL-1ß-negative during phagocytosis of apoptotic cells. The data demonstrate that phagocytic activity and pro-inflammatory microglial phenotype do not necessarily correlate.

Cognitive deficits in adult m.3243A>G- and m.8344A>G-related mitochondrial disease: importance of correcting for baseline intellectual ability.

OBJECTIVE: To determine the cognitive profile of adult patients with mitochondrial disease, and the effect of disease severity on cognition. METHODS: Using a prospective case-control design, we compared cognition of patients to normative data and to matched controls, assessed three times over 18 months. Forty-nine patients with m.3243A>G (N = 36) and m.8344A>G (N = 13) mtDNA mutations and 32 controls, matched by age (±5 years) and premorbid cognition (±10 WTAR FSIQ points), participated. Participants completed neuropsychological assessments of general cognition (WAIS-IV), executive function (D-KEFS), and memory (WMS-IV). Potential predictors of cognition were explored. RESULTS: Patients show mild-to-moderate premorbid cognitive impairment, but substantial impairment in current general cognition and distinct domains, including verbal comprehension, perceptual reasoning, working memory, processing speed, and memory retrieval. Executive dysfunction may be caused by slower decision-making. Patients performed worse than controls, except on memory tasks, indicating intact memory, when premorbid cognition is controlled for. Premorbid cognition and disease severity were consistent predictors of cognition in patients; however, cognitive decline appears slow and is unlikely in the short-term, when other disease-specific factors remain stable. INTERPRETATION: Patients should be monitored to facilitate early identification of a complex profile of cognitive deficits and individuals with higher disease burden should be followed up more closely. On development of cognitive difficulties, appropriate compensatory strategies should be determined through in-depth assessment. Using strategies such as slower presentation of information, multiple modes of presentation, active discussion to aid understanding and decision-making, and use of memory aids, may ameliorate difficulties.

A spatial covariance 123I-5IA-85380 SPECT study of α4ß2 nicotinic receptors in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by widespread degeneration of cholinergic neurons, particularly in the basal forebrain. However, the pattern of these deficits and relationship with known brain networks is unknown. In this study, we sought to clarify this and used 123I-5-iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (1235IA-85380) single photon emission computed tomography to investigate spatial covariance of α4ß2 nicotinic acetylcholine receptors in AD and healthy controls. Thirteen AD and 16 controls underwent 1235IA-85380 and regional cerebral blood flow (99mTc-exametazime) single photon emission computed tomography scanning. We applied voxel principal component (PC) analysis, generating series of principal component images representing common intercorrelated voxels across subjects. Linear regression generated specific α4ß2 and regional cerebral blood flow covariance patterns that differentiated AD from controls. The α4ß2 pattern showed relative decreased uptake in numerous brain regions implicating several networks including default mode, salience, and Papez hubs. Thus, as well as basal forebrain and brainstem cholinergic system dysfunction, cholinergic deficits mediated through nicotinic acetylcholine receptors could be evident within key networks in AD. These findings may be important for the pathophysiology of AD and its associated cognitive and behavioral phenotypes.