MiRNA research-The potential for understanding the multiple facets of anorexia nervosa.

Anorexia nervosa (AN) has a multifaceted and complex pathology, yet major gaps remain in our understanding of factors involved in AN pathology. MicroRNAs (miRNAs) play a regulatory role in translating genes into proteins and help understand and treat diseases. An extensive literature review on miRNAs with AN and comorbidities has uncovered a significant lack in miRNA research. To demonstrate the importance of understanding miRNA deregulation, we surveyed the literature on depression and obesity providing examples of relevant miRNAs. For AN, no miRNA sequencing or array studies have been found, unlike other psychiatric disorders. For depression and obesity, screenings and mechanistic studies were conducted, leading to clinical studies to improve understanding of their regulatory influences. MiRNAs are promising targets for studying AN due to their role as signaling molecules, involvement in psychiatric-metabolic axes, and potential as biomarkers. These characteristics offer valuable insights into the disease's etiology and potential new treatment options. The first miRNA-based treatment for rare metabolic disorders has been approved by the FDA and it is expected that these advancements will increase in the next decade. MiRNA research in AN is essential to examine its role in the development, manifestation, and progression of the disease. PUBLIC SIGNIFICANCE: The current understanding of the development and treatment of AN is insufficient. miRNAs are short regulatory sequences that influence the translation of genes into proteins. They are the subject of research in various diseases, including both metabolic and psychiatric disorders. Studying miRNAs in AN may elucidate their causal and regulatory role, uncover potential biomarkers, and allow for future targeted treatments.

Gut-Associated Lymphatic Tissue in Food-Restricted Rats: Influence of Refeeding and Probiotic Supplementation.

Anorexia nervosa (AN) is a severe and often chronic eating disorder that leads to alterations in the gut microbiome, which is known to influence several processes, such as appetite and body weight regulation, metabolism, gut permeability, inflammation, and gut-brain interactions. Using a translational activity-based anorexia (ABA) rat model, this study examined the effect of chronic food starvation, as well as multistrain probiotic supplementation and refeeding, on the structure of the gut and gut-associated lymphatic tissue (GALT). Our results indicated that ABA had an atrophic influence on intestinal morphology and increased the formation of GALT in the small bowel and colon. Higher formation of GALT in ABA rats appeared to be reversible upon application of a multistrain probiotic mixture and refeeding of the starved animals. This is the first time that increased GALT was found following starvation in the ABA model. Our results underscore a potential role of gut inflammatory alterations in the underlying pathophysiology of AN. Increased GALT could be linked to the gut microbiome, as probiotics were able to reverse this finding. These results emphasize the role of the microbiome-gut-brain axis in the pathomechanisms of AN and point to probiotics as potentially beneficial addendum in the treatment of AN.

Lipocalin-2 Deficiency Diminishes Canonical NLRP3 Inflammasome Formation and IL-1ß Production in the Subacute Phase of Spinal Cord Injury.

Spinal cord injury (SCI) results in the production of proinflammatory cytokines due to inflammasome activation. Lipocalin 2 (LCN2) is a small secretory glycoprotein upregulated by toll-like receptor (TLR) signaling in various cells and tissues. LCN2 secretion is induced by infection, injury, and metabolic disorders. In contrast, LCN2 has been implicated as an anti-inflammatory regulator. However, the role of LCN2 in inflammasome activation during SCI remains unknown. This study examined the role of Lcn2 deficiency in the NLRP3 inflammasome-dependent neuroinflammation in SCI. Lcn2-/- and wild-type (WT) mice were subjected to SCI, and locomotor function, formation of the inflammasome complex, and neuroinflammation were assessed. Our findings demonstrated that significant activation of the HMGB1/PYCARD/caspase-1 inflammatory axis was accompanied by the overexpression of LCN2 7 days after SCI in WT mice. This signal transduction results in the cleaving of the pyroptosis-inducing protein gasdermin D (GSDMD) and the maturation of the proinflammatory cytokine IL-1ß. Furthermore, Lcn2-/- mice showed considerable downregulation in the HMGB1/NLRP3/PYCARD/caspase-1 axis, IL-1ß production, pore formation, and improved locomotor function compared with WT. Our data suggest that LCN2 may play a role as a putative molecule for the induction of inflammasome-related neuroinflammation in SCI.

Astrocytic Nrf2 expression protects spinal cord from oxidative stress following spinal cord injury in a male mouse model.

BACKGROUND: Spinal cord injury (SCI) induces a multitude of deleterious processes, including neuroinflammation and oxidative stress (OS) which contributed to neuronal damage and demyelination. Recent studies have suggested that increased formation of reactive oxygen species (ROS) and the consequent OS are critical events associated with SCI. However, there is still little information regarding the impact of these events on SCI. Astrocytes are key regulators of oxidative homeostasis in the CNS and astrocytic antioxidant responses promote the clearance of oxidants produced by neurons. Therefore, dysregulation of astrocyte physiology might largely contribute to oxidative damage. Nuclear factor erythroid 2-related factor 2 (Nrf2) is the main transcriptional regulator of cellular anti-oxidative stress responses. METHODS: In the current study, we hypothesized that astrocytic activation of Nrf2 protects the spinal cord post injury via suppression of neuroinflammation. Thus, using mice line with a GFAP-specific kelch-like ECH-associated protein 1 (Keap1)-deletion, we induced a hyperactivation of Nrf2 in astrocytes and further its effects on SCI outcomes. SCI-induction was performed in mice using the Infinite Horizon Spinal Cord Impactor with a force of 60 kdyn. To assess the quantitative pattern of Nrf2/ARE-activation, we included transgenic ARE-Luc mice. Data were analyzed with GraphPad Prism 8 (GraphPad Software Inc., San Diego, CA, USA). Brown-Forsythe test was performed to test for equal variances and normal distribution was tested with Shapiro-Wilk. RESULTS: In ARE-Luc mice, a significant induction of luciferase-activity was observed as early as 1 day post-injury, indicating a functional role of Nrf2-activity at the epicenter of SCI. Furthermore, SCI induced loss of neurons and oligodendrocytes, demyelination and inflammation in wild type mice. The loss of myelin and oligodendrocytes was clearly reduced in Keap1 KO mice. In addition, Keap-1 KO mice showed a significantly better locomotor function and lower neuroinflammation responses compared to wild type mice. CONCLUSIONS: In summary, our in vivo bioluminescence data showed Nrf2-ARE activation during primary phase of SCI. Furthermore, we found that cell specific hyperactivation of Nrf2 was sufficient to protect the spinal cord against injury which indicate a promising therapeutic approach for SCI-treatment.

Fear and food: Anxiety-like behavior and the susceptibility to weight loss in an activity-based anorexia rat model.

Anorexia nervosa (AN) is a severe psychiatric disorder characterized by energy restriction, low body weight, a fear of gaining weight, and often excessive physical activity. Anxiety disorders appear to constitute a major risk factor for developing AN and are the most frequent comorbidity. Here, the influence of anxiety-like behavior prior to food restriction on increased physical activity, leading to greater susceptibility to weight loss, was tested in rats. Furthermore, the possible anxiolytic effect of starvation itself was analyzed. A chronic starvation model activity-based anorexia (ABA) was applied to mimic physiological and behavioral characteristics of AN. During the induction of starvation and acute starvation, food intake was reduced by 70% and the rats lost 25% of their body weight, which was kept stable to imitate chronic starvation. Anxiety-like behavior was quantified before and after chronic starvation using the elevated plus maze, based on rodents' aversion to open spaces. Anxiety-related behavior before food restriction was associated with increased running-wheel activity during habituation and during the induction of starvation, and predicted faster weight loss in ABA rats. Additionally, food-restricted animals showed less anxiety-like behavior after chronic starvation. Animals showing more anxiety-like behavior appear to be more susceptible to weight loss, partially mediated by increased physical activity. Anxiety-related behavior was associated with increased physical activity, which in turn was associated with more rapid weight loss. Our data let us assume that food restriction has an anxiolytic effect. These findings demonstrate the importance of considering anxiety disorders in patients with AN.

Lipocalin 2 as a Putative Modulator of Local Inflammatory Processes in the Spinal Cord and Component of Organ Cross talk After Spinal Cord Injury.

Lipocalin 2 (LCN2), an immunomodulator, regulates various cellular processes such as iron transport and defense against bacterial infection. Under pathological conditions, LCN2 promotes neuroinflammation via the recruitment and activation of immune cells and glia, particularly microglia and astrocytes. Although it seems to have a negative influence on the functional outcome in spinal cord injury (SCI), the extent of its involvement in SCI and the underlying mechanisms are not yet fully known. In this study, using a SCI contusion mouse model, we first investigated the expression pattern of Lcn2 in different parts of the CNS (spinal cord and brain) and in the liver and its concentration in blood serum. Interestingly, we could note a significant increase in LCN2 throughout the whole spinal cord, in the brain, liver, and blood serum. This demonstrates the diversity of its possible sites of action in SCI. Furthermore, genetic deficiency of Lcn2 (Lcn2-/-) significantly reduced certain aspects of gliosis in the SCI-mice. Taken together, our studies provide first valuable hints, suggesting that LCN2 is involved in the local and systemic effects post SCI, and might modulate the impairment of different peripheral organs after injury.

Aggregated Tau-PHF6 (VQIVYK) Potentiates NLRP3 Inflammasome Expression and Autophagy in Human Microglial Cells.

Intra-neuronal misfolding of monomeric tau protein to toxic ß-sheet rich neurofibrillary tangles is a hallmark of Alzheimer's disease (AD). Tau pathology correlates not only with progressive dementia but also with microglia-mediated inflammation in AD. Amyloid-beta (Aß), another pathogenic peptide involved in AD, has been shown to activate NLRP3 inflammasome (NOD-like receptor family, pyrin domain containing 3), triggering the secretion of proinflammatory interleukin-1ß (IL1ß) and interleukin-18 (IL18). However, the effect of tau protein on microglia concerning inflammasome activation, microglial polarization, and autophagy is poorly understood. In this study, human microglial cells (HMC3) were stimulated with the unaggregated and aggregated forms of the tau-derived PHF6 peptide (VQIVYK). Modulation of NLRP3 inflammasome was examined by qRT-PCR, immunocytochemistry, and Western blot. We demonstrate that fibrillar aggregates of VQIVYK upregulated the NLRP3 expression at both mRNA and protein levels in a dose- and time-dependent manner, leading to increased expression of IL1ß and IL18 in HMC3 cells. Aggregated PHF6-peptide also activated other related inflammation and microglial polarization markers. Furthermore, we also report a time-dependent effect of the aggregated PHF6 on BECN1 (Beclin-1) expression and autophagy. Overall, the PHF6 model system-based study may help to better understand the complex interconnections between Alzheimer's PHF6 peptide aggregation and microglial inflammation, polarization, and autophagy.

Transient Focal Cerebral Ischemia Leads to miRNA Alterations in Different Brain Regions, Blood Serum, Liver, and Spleen.

Ischemic stroke is characterized by an occlusion of a cerebral blood vessel resulting in neuronal cell death due to nutritional and oxygen deficiency. Additionally, post-ischemic cell death is augmented after reperfusion. These events are paralleled by dysregulated miRNA expression profiles in the peri-infarct area. Understanding the underlying molecular mechanism in the peri-infarct region is crucial for developing promising therapeutics. Utilizing a tMCAo (transient Middle Cerebral Artery occlusion) model in rats, we studied the expression levels of the miRNAs (miR) 223-3p, 155-5p, 3473, and 448-5p in the cortex, amygdala, thalamus, and hippocampus of both the ipsi- and contralateral hemispheres. Additionally, the levels in the blood serum, spleen, and liver and the expression of their target genes, namely, Nlrp3, Socs1, Socs3, and Vegfa, were assessed. We observed an increase in all miRNAs on the ipsilateral side of the cerebral cortex in a time-dependent manner and increased miRNAs levels (miR-223-3p, miR-3473, and miR-448-5p) in the contralateral hemisphere after 72 h. Besides the cerebral cortex, the amygdala presented increased expression levels, whereas the thalamus and hippocampus showed no alterations. Different levels of the investigated miRNAs were detected in blood serum, liver, and spleen. The gene targets were altered not only in the peri-infarct area of the cortex but selectively increased in the investigated non-affected brain regions along with the spleen and liver during the reperfusion time up to 72 h. Our results suggest a supra-regional influence of miRNAs following ischemic stroke, which should be studied to further identify whether miRNAs are transported or locally upregulated.

Alteration of miRNA Biogenesis Regulating Proteins in the Human Microglial Cell Line HMC-3 After Ischemic Stress.

MicroRNAs (miRNA) are small noncoding sequences that control apoptosis, proliferation, and neuroinflammatory pathways in microglia cells. The expression of distinct miRNAs is altered after ischemia in the brain. Only minor information is available about the biogenesis and maturation of miRNAs after ischemia. We aimed at examining the impact of oxygen-glucose deprivation (OGD) and hydrogen peroxide (H2O2)-induced stress on the expression of miRNA regulating proteins such as DROSHA, DGCR8, XPO5, DICER, TARBP2, and AGO2 in the cultured human microglial cell line HMC-3 (human microglial cell line clone 3). OGD duration of 2.5 h or H2O2 stimulation at a concentration of 100 µM for 24 h resulted in a marked increase of the hypoxia sensor hypoxia-inducible factor1-α in HMC-3 cells. These treatments also led to an upregulation of DROSHA, DICER1, and AGO2 detected by semiquantitative real-time PCR (qrtPCR). XPO5 and TARBP2 were only upregulated after stimulation with H2O2, while DGCR8 responded only to OGD. We found elevated DICER1, DROSHA, and AGO2 protein levels by western blot and immunohistochemistry staining. Interestingly, the latter also exposed a colocalization of AGO2 with stress granules (G3BP1) after OGD. Our data indicate that DICER, DROSHA, and AGO2 are induced in microglial cells under hypoxia-like conditions. It might be speculated that their inductions might increase the miRNA synthesis rate. Future studies should investigate this correlation to determine which miRNAs are preferably expressed by microglia cells after ischemia and which functions they could exert.

Gut microbiota and brain alterations in a translational anorexia nervosa rat model.

Anorexia nervosa (AN) is an eating disorder that leads to brain volume reduction and is difficult to treat since the underlying pathophysiology is poorly understood. The human gut microbiota is known to be involved in host metabolism, appetite- and bodyweight regulation, gut permeability, inflammation and gut-brain interactions. In this study, we used a translational activity-based anorexia (ABA) rat model including groups with food restriction, running-wheel access and a combination to disentangle the influences on the gut microbiota and associated changes in brain volume parameters. Our data demonstrated that chronic food restriction but not running-wheel activity had a major influence on the gut microbiota diversity and composition and reduced brain volume. Negative correlations were found between global brain weight and α-diversity, and astrocyte markers and relative abundances of the genera Odoribacter and Bifidobacterium. In contrast, the presence of lactobacilli was positively associated with white and grey brain matter volume. ABA and food-restricted rats are an interesting pre-clinical model to assess the causal influence of starvation on the gut microbiome and gut-brain interactions and can help to dissect the underlying pathophysiologic mechanisms relevant to AN.

NLRP3 Depletion Fails to Mitigate Inflammation but Restores Diminished Phagocytosis in BV-2 Cells After In Vitro Hypoxia.

Post-hypoxic/ischemic neuroinflammation is selectively driven by sterile inflammation, which implies the interplay of brain-intrinsic immune cells with other neural cells and immigrated peripheral immune cells. The resultant inflammatory cascade evolves extra- and intracellular pathogen and danger-associated receptors. The latter interacts with multiprotein complexes termed inflammasomes. The NLRP3 inflammasome is one of the best-described inflammasomes. However, its impact on post-ischemic neuroinflammation and its role in neuroprotection after ischemic stroke are still under debate. Microglial cells are known to be the main source of neuroinflammation; hence, we depleted NLRP3 in BV-2 microglial cells using shRNA to investigate its role in IL-1ß maturation and phagocytosis after hypoxia (oxygen-glucose-deprivation (OGD)). We also examined the expression profiles of other inflammasomes (NLRC4, AIM2, ASC) and caspase-1 activity after OGD. OGD triggered caspase-1 activity and increased IL-1ß secretion in BV-2 cells with no alteration after NLRP3 depletion. The expression of the AIM2 inflammasome was significantly higher after OGD in NLRP3-depleted cells, whereas NLRC4 was unaltered in all groups. Interestingly, OGD induced a complete inactivation of phagocytic activity in wild-type cells, while in NLRP3-depleted BV-2, this inactivity was restored after hypoxia. Our findings indicate a minor role of NLRP3 in the inflammatory response after hypoxic/ischemic stimulus. However, NLRP3 seems to play a pivotal role in the regulation of post-ischemic phagocytosis. This might be a prerequisite for the putative neuroprotective effect.