Jose Felix Moruno-Manchon

Gradual reduction of cerebral blood flow occurs with aging, and it is a major cause of vascular dementia, a group of dementias with a cerebrovascular component. Interestingly, patients who have suffered a vascular insult may develop retinopathy, which may occur as an early symptom of vascular dementia. Several rodent models using young animals have been generated to mimic retinopathy caused by cerebral hypoperfusion; however, given that aging is an important factor in developing vascular dementia and hypoperfusion retinopathy, we propose to use aged (17-month-old) mice in a model of cerebral hypoperfusion. In this model, we implant two metallic micro-coils (0.16 mm inner diameter) around both common carotid arteries. We found that two months after surgery, aged mice with bilateral carotid artery stenosis (BCAS) showed hyperactivity-like behavior, cognitive deficits, and demyelination, which are pathological features in patients with vascular dementia. We also found that the retina of BCAS mice showed important morphological changes, such as reduced area of the outer synaptic layer, retraction of rod photoreceptor terminals, and increased sprouting of rod bipolar cells. BCAS mice also showed reduced in vivo retinal responses to different light intensities. Our study is the first to propose using aged mice in a model of hypoperfusion retinopathy, which is relevant to identifying the molecular mechanisms underlying vision loss with cerebral hypoperfusion.

Objective: Iron is the most abundant metal in the human brain, and plays a crucial role in many biological processes. However, disruptions in brain iron metabolism can lead to iron buildup, which occurs with aging and is linked to several brain disorders, including Alzheimer's disease. Microglia, the brain's resident immune cells, have the highest capacity to store iron, which is stored intracellularly within ferritin complexes. Importantly, women are at a higher risk of developing Alzheimer's disease and experience faster disease progression compared to men. Methods: We used postmortem brain samples from patients with Alzheimer's disease and small vessel disease patients of both sexes for immunohistochemical studies. Samples were stained with the Prussian blue method to visualize iron deposits and with antibodies against the microglia marker Iba1 and ferritin light chain. Results: Our study reveals that the number of iron deposits and the levels of ferritin light chain in microglia are positively correlated in men with Alzheimer's disease, but negatively correlated in women. There is no correlation between brain iron deposition and ferritin in samples from patients with small vessel disease of both sexes. Conclusions: These results could inform more tailored approaches to the treatment and management of Alzheimer's disease based on sex-specific differences in brain iron metabolism and microglial iron storage capacity.

As we age, cerebral endothelial cells (CECs) are less efficient in maintaining genome integrity and accumulate DNA damage. DNA damage in the brain endothelium can lead to the impairment of the blood–brain barrier (BBB), which is a major factor in brain dysfunction and dementia. Thus, identifying factors that regulate DNA repair in the brain endothelium can prevent brain dysfunction associated with aging. E2F1 is a transcription factor that regulates the expression of genes associated with DNA repair, among other functions. We hypothesize that E2F1 is downregulated in the brain vasculature of mice with aging and that E2F1 upregulation can improve cognitive function. We found that in the brain endothelium, E2F1 was significantly less phosphorylated, which is associated with its transcriptional activity, in the brain vasculature of aged mice and cultured CEC derived from aged mice compared with those from young mice. We found that E2f1 overexpression reduced DNA damage in cultured CEC, and targeting the brain vasculature to overexpress E2f1 improved cognition and increased the expression of genes associated with BBB integrity in aged mice. From RNA sequencing data from cultured CEC, we found that E2f1 overexpression significantly upregulated Acod1 , which codes for aconitate decarboxylase‐1 (ACOD1), an enzyme that produces itaconate. We also found that 4‐octyl itaconate (4‐OI), a derivative of itaconate, reduced DNA damage, promoted cell proliferation, and restored endothelial barrier function from oxidative stress in cultured CEC. Thus, our study identifies the E2F1‐ACOD1 axis as a molecular pathway that can protect the brain endothelium from oxidative stress and aging.

Stroke is the most common cause of long-term disability and places a high economic burden on the global healthcare system. Functional outcomes from stroke are largely determined by the extent of ischemic injury, however, there is growing recognition that systemic inflammatory responses also contribute to outcomes. Mast cells (MCs) rapidly respond to injury and release histamine (HA), a pro-inflammatory neurotransmitter that enhances inflammation. The gut serves as a major reservoir of HA. We hypothesized that cromolyn, a mast cell stabilizer that prevents the release of inflammatory mediators, would decrease peripheral and central inflammation, reduce MC trafficking to the brain, and improve stroke outcomes. We used the transient middle cerebral artery occlusion (MCAO) model of ischemic stroke in aged (18 mo) male mice to investigate the role of MC in neuroinflammation post-stroke. After MCAO we treated mice with 25 mg/kg body weight of cromolyn (MC stabilizer) by oral gavage. Cromolyn was administered at 3 h, 10 h, 24 h and every 24 h for 3 days post-stroke. Three control groups were used. One group underwent a sham surgery and was treated with cromolyn, one received sham surgery with PBS vehicle and the third underwent MCAO with PBS vehicle. Mice were euthanized at 24 h and 3 days post-stroke. Cromolyn administration significantly reduced MC numbers in the brain at both 24 h and 3 days post-stroke. Infarct volume was not significantly different between groups, however improved functional outcomes were seen at 3 days post-stroke in mice that received cromolyn. Treatment with cromolyn reduced plasma histamine and IL-6 levels in both the 24-h and 3-day cohorts. Gut MCs numbers were significantly reduced after cromolyn treatment at 24 h and 3 days after stroke. To determine if MC trafficking from the gut to the brain occurred after injury, GFP⁺MCs were adoptively transferred to c-kit^−/− MC knock-out animals prior to MCAO. 24 h after stroke, elevated MC recruitment was seen in the ischemic brain. Preventing MC histamine release by cromolyn improved gut barrier integrity and an improvement in stroke-induced dysbiosis was seen with treatment. Our results show that preventing MC histamine release possesses prevents post-stroke neuroinflammation and improves neurological and functional outcomes. Graphical abstract

Iron imbalance in the brain negatively affects brain function. With aging, iron levels increase in the brain and contribute to brain damage and neurological disorders. Changes in the cerebral vasculature with aging may enhance iron entry into the brain parenchyma, leading to iron overload and its deleterious consequences. Endothelial senescence has emerged as an important contributor to age‐related changes in the cerebral vasculature. Evidence indicates that iron overload may induce senescence in cultured cell lines. Importantly, cells derived from female human and mice generally show enhanced senescence‐associated phenotype, compared with males. Thus, we hypothesize that cerebral endothelial cells (CEC) derived from aged female mice are more susceptible to iron‐induced senescence, compared with CEC from aged males. We found that aged female mice, but not males, showed cognitive deficits when chronically treated with ferric citrate (FC), and their brains and the brain vasculature showed senescence‐associated phenotype. We also found that primary culture of CEC derived from aged female mice, but not male‐derived CEC, exhibited senescence‐associated phenotype when treated with FC. We identified that the transmembrane receptor Robo4 was downregulated in the brain vasculature and in cultured primary CEC derived from aged female mice, compared with those from male mice. We discovered that Robo4 downregulation contributed to enhanced vulnerability to FC‐induced senescence. Thus, our study identifies Robo4 downregulation as a driver of senescence induced by iron overload in primary culture of CEC and a potential risk factor of brain vasculature impairment and brain dysfunction.

Stroke is the second leading cause of death and a major cause of disability worldwide, and biological sex is an important determining factor in stroke incidence and pathology. From childhood through adulthood, men have a higher incidence of stroke compared with women. Abundant research has confirmed the beneficial effects of estrogen in experimental ischemic stroke but genetic factors such as the X-chromosome complement can also play an important role in determining sex differences in stroke. Autophagy is a self-degrading cellular process orchestrated by multiple core proteins, which leads to the engulfment of cytoplasmic material and degradation of cargo after autophagy vesicles fuse with lysosomes or endosomes. The levels and the activity of components of these signaling pathways and of autophagy-related proteins can be altered during ischemic insults. Ischemic stroke activates autophagy, however, whether inhibiting autophagy after stroke is beneficial in the brain is still under a debate. Autophagy is a potential mechanism that may contribute to differences in stroke progression between the sexes. Furthermore, the effects of manipulating autophagy may also differ between the sexes. Mechanisms that regulate autophagy in a sex-dependent manner in ischemic stroke remain unexplored. In this review, we summarize clinical and pre-clinical evidence for sex differences in stroke. We briefly introduce the autophagy process and summarize the effects of gonadal hormones in autophagy in the brain and discuss X-linked genes that could potentially regulate brain autophagy. Finally, we review pre-clinical studies that address the mechanisms that could mediate sex differences in brain autophagy after stroke.

Senescence in the cerebral endothelium has been proposed as a mechanism that can drive dysfunction of the cerebral vasculature, which precedes vascular dementia. Cysteine-rich angiogenic inducer 61 (Cyr61/CCN1) is a matricellular protein secreted by cerebral endothelial cells (CEC). CCN1 induces senescence in fibroblasts. However, whether CCN1 contributes to senescence in CEC and how this is regulated requires further study. Aging has been associated with the formation of four-stranded Guanine-quadruplexes (G4s) in G-rich motifs of DNA and RNA. Stabilization of the G4 structures regulates transcription and translation either by upregulation or downregulation depending on the gene target. Previously, we showed that aged mice treated with a G4-stabilizing compound had enhanced senescence-associated (SA) phenotypes in their brains, and these mice exhibited enhanced cognitive deficits. A sequence in the 3′-UTR of the human CCN1 mRNA has the ability to fold into G4s in vitro. We hypothesize that G4 stabilization regulates CCN1 in cultured primary CEC and induces endothelial senescence. We used cerebral microvessel fractions and cultured primary CEC from young (4-months old, m/o) and aged (18-m/o) mice to determine CCN1 levels. SA phenotypes were determined by high-resolution fluorescence microscopy in cultured primary CEC, and we used Thioflavin T to recognize RNA-G4s for fluorescence spectra. We found that cultured CEC from aged mice exhibited enhanced levels of SA phenotypes, and higher levels of CCN1 and G4 stabilization. In cultured CEC, CCN1 induced SA phenotypes, such as SA β-galactosidase activity, and double-strand DNA damage. Furthermore, CCN1 levels were upregulated by a G4 ligand, and a G-rich motif in the 3′-UTR of the Ccn1 mRNA was folded into a G4. In conclusion, we demonstrate that CCN1 can induce senescence in cultured primary CEC, and we provide evidence that G4 stabilization is a novel mechanism regulating the SASP component CCN1.

Ischemic stroke triggers a series of complex pathophysiological processes including autophagy. Differential activation of autophagy occurs in neurons derived from males versus females after stressors such as nutrient deprivation. Whether autophagy displays sexual dimorphism after ischemic stroke is unknown. We used a cerebral ischemia mouse model (middle cerebral artery occlusion, MCAO) to evaluate the effects of inhibiting autophagy in ischemic brain pathology. We observed that inhibiting autophagy reduced infarct volume in males and ovariectomized females. However, autophagy inhibition enhanced infarct size in females and in ovariectomized females supplemented with estrogen compared to control mice. We also observed that males had increased levels of Beclin1 and LC3 and decreased levels of pULK1 and p62 at 24 h, while females had decreased levels of Beclin1 and increased levels of ATG7. Furthermore, the levels of autophagy markers were increased under basal conditions and after oxygen and glucose deprivation in male neurons compared with female neurons in vitro. E2 supplementation significantly inhibited autophagy only in male neurons, and was beneficial for cell survival only in female neurons. This study shows that autophagy in the ischemic brain differs between the sexes, and that autophagy regulators have different effects in a sex-dependent manner in neurons.