Moderate Protein Restriction Protects Against Focal Cerebral Ischemia in Mice by Mechanisms Involving Anti-inflammatory and Anti-oxidant Responses

Neurotoxicity of ischemic astrocytes involves STAT3-mediated metabolic switching and depends on glycogen usage

Astrocytic responses are critical for the maintenance of neuronal networks in health and disease. In stroke, reactive astrocytes undergo functional changes potentially contributing to secondary neurodegeneration, but the mechanisms of astrocyte-mediated neurotoxicity remain elusive. Here, we investigated metabolic reprogramming in astrocytes following ischemia-reperfusion in vitro, explored their role in synaptic degeneration, and verified the key findings in a mouse model of stroke. Using indirect cocultures of primary mouse astrocytes and neurons, we demonstrate that transcription factor STAT3 controls metabolic switching in ischemic astrocytes promoting lactate-directed glycolysis and hindering mitochondrial function. Upregulation of astrocytic STAT3 signaling associated with nuclear translocation of pyruvate kinase isoform M2 and hypoxia response element activation. Reprogrammed thereby, the ischemic astrocytes induced mitochondrial respiration failure in neurons and triggered glutamatergic synapse loss, which was prevented by inhibiting astrocytic STAT3 signaling with Stattic. The rescuing effect of Stattic relied on the ability of astrocytes to utilize glycogen bodies as an alternative metabolic source supporting mitochondrial function. After focal cerebral ischemia in mice, astrocytic STAT3 activation was associated with secondary synaptic degeneration in the perilesional cortex. Inflammatory preconditioning with LPS increased astrocytic glycogen content, reduced synaptic degeneration, and promoted neuroprotection post stroke. Our data indicate the central role of STAT3 signaling and glycogen usage in reactive astrogliosis and suggest novel targets for restorative stroke therapy.

Rho-Kinase inhibition decreases focal cerebral ischemia-induced glial activation in rats

Background

Rho-kinase inhibition in a rat middle cerebral artery occlusion (MCAO) model is reported to improve neurological functions and decrease infarction size.

Objective

The objective of this study is to investigate the underlying mechanisms of such improvement by evaluating the effects of Rho-kinase inhibition on astrocytes and microglial accumulation and activation in this condition.

Methods

Adult male Sprague-Dawley (SD) rats were used to generate the MCAO model, which received an I.P injection of a chemical Rho-kinase inhibitor (Fasudil- 5 mg/kg/day) or vehicle (PBS) for 2 and 4 days.

Results

Fasudil treatment significantly decreased the stroke volumes and water content in the lesion areas, as revealed by MRI. Immunostaining and Western blotting results demonstrated that Fasudil significantly decreased the levels of Aquaporin-4, a water channel protein. The number of GFAP⁺ astrocytes and Iba-1⁺ macrophage/microglia was decreased in the lesion areas. Proinflammatory transcription factor NF-κB protein levels were decreased in the Fasudil group 2 days after MCAO. Also, proinflammatory mediators including TNF-α, IL-1β, and iNOS levels were decreased. In vitro migration study using a human microglial cell line (HMO6) confirmed the inhibitory effects of Fasudil on the process. Fasudil also decreased combined IL-1β and IFNγ-induced NF-κB nuclear translocation in HMO6. Moreover, Fasudil transiently decreased combined IL-1β and IFNγ-induced iNOS, TNFα, and IL-1β mRNA levels in HMO6.

Conclusion

Our study demonstrates the inhibitory effects of Rho-kinase on NF-κB-mediated glial activation and cerebral edema, which might be a promising therapeutic target in acute cerebral ischemia conditions.

Post-ischemic protein restriction induces sustained neuroprotection, neurological recovery, brain remodeling, and gut microbiota rebalancing

BACKGROUND

Moderate dietary protein restriction confers neuroprotection when applied before ischemic stroke. How a moderately protein-reduced diet influences stroke recovery when administered after stroke, is a clinically relevant question. This question has not yet been investigated.

METHODS

Male C57BL6/J mice were exposed to transient intraluminal middle cerebral artery occlusion. Immediately after the stroke, mice were randomized to two normocaloric diets: a moderately protein-reduced diet containing 8% protein (PRD) or normal diet containing 20% protein (ND). Post-stroke neurological deficits were evaluated by a comprehensive test battery. Antioxidant and neuroinflammatory responses in the brain and liver were evaluated by Western blot and RTqPCR. Stroke-induced brain injury, microvascular integrity, glial responses, and neuroplasticity were assessed by immunohistochemistry. Fecal microbiota analysis was performed using 16S ribosomal RNA amplicon sequencing.

RESULTS

We show that PRD reduces brain infarct volume after three days and enhances neurological and, specifically, motor-coordination recovery over six weeks in stroke mice. The recovery-promoting effects of PRD were associated with increased antioxidant responses and reduced neuroinflammation. Histochemical studies revealed that PRD increased long-term neuronal survival, increased peri-infarct microvascular density, reduced microglia/macrophage accumulation, increased contralesional pyramidal tract plasticity, and reduced brain atrophy. Fecal microbiota analysis showed reduced bacterial richness and diversity in ischemic mice on ND starting at 7 dpi. PRD restored bacterial richness and diversity at these time points.

CONCLUSION

Moderate dietary protein restriction initiated post-ischemic stroke induces neurological recovery, brain remodeling, and neuroplasticity in mice by mechanisms involving antiinflammation and, in the post-acute phase, commensal gut microbiota rebalancing.

Calorie restriction or dietary restriction: how far they can protect the brain against neurodegenerative diseases?

Finding the correct nutritional intervention is one of the biggest challenges in treating patients with neurodegenerative diseases. In general, these patients develop strong metabolic alterations, resulting in lower treatment efficacy and higher mortality rates. However, there are still many open questions regarding the effectiveness of dietary interventions in neurodiseases. Some studies have shown that a reduction in calorie intake activates key pathways that might be important for preventing or slowing down the progression of such diseases. However, it is still unclear whether these neuroprotective effects are associated with an overall reduction in calories (hypocaloric diet) or a specific nutrient restriction (diet restriction). Therefore, here we discuss how commonly or differently hypocaloric and restricted diets modulate signaling pathways and how these changes can protect the brain against neurodegenerative diseases.

Sirtuins-Mediated System-Level Regulation of Mammalian Tissues at the Interface between Metabolism and Cell Cycle: A Systematic Review

Sirtuins are a family of highly conserved NAD+-dependent proteins and this dependency links Sirtuins directly to metabolism. Sirtuins' activity has been shown to extend the lifespan of several organisms and mainly through the post-translational modification of their many target proteins, with deacetylation being the most common modification. The seven mammalian Sirtuins, SIRT1 through SIRT7, have been implicated in regulating physiological responses to metabolism and stress by acting as nutrient sensors, linking environmental and nutrient signals to mammalian metabolic homeostasis. Furthermore, mammalian Sirtuins have been implicated in playing major roles in mammalian pathophysiological conditions such as inflammation, obesity and cancer. Mammalian Sirtuins are expressed heterogeneously among different organs and tissues, and the same holds true for their substrates. Thus, the function of mammalian Sirtuins together with their substrates is expected to vary among tissues. Any therapy depending on Sirtuins could therefore have different local as well as systemic effects. Here, an introduction to processes relevant for the actions of Sirtuins, such as metabolism and cell cycle, will be followed by reasoning on the system-level function of Sirtuins and their substrates in different mammalian tissues. Their involvement in the healthy metabolism and metabolic disorders will be reviewed and critically discussed.

Will Sirtuins Be Promising Therapeutic Targets for TBI and Associated Neurodegenerative Diseases?

Traumatic brain injury (TBI), a leading cause of morbidity worldwide, induces mechanical, persistent structural, and metabolic abnormalities in neurons and other brain-resident cells. The key pathological features of TBI include neuroinflammation, oxidative stress, excitotoxicity, and mitochondrial dysfunction. These pathological processes persist for a period of time after TBIs. Sirtuins are evolutionarily conserved nicotinamide-adenine dinucleotide (NAD+)-dependent deacetylases and mono-ADP-ribosyl transferases. The mammalian sirtuin family has seven members, referred to as Sirtuin (SIRT) 1-7. Accumulating evidence suggests that SIRT1 and SIRT3 play a neuroprotective role in TBI. Although the evidence is scant, considering the involvement of SIRT2, 4-7 in other brain injury models, they may also intervene in similar pathophysiology in TBI. Neurodegenerative diseases are generally accepted sequelae of TBI. It was found that TBI and neurodegenerative diseases have many similarities and overlaps in pathological features. Besides, sirtuins play some unique roles in some neurodegenerative diseases. Therefore, we propose that sirtuins might be a promising therapeutic target for both TBI and associated neurodegenerative diseases. In this paper, we review the neuroprotective effects of sirtuins on TBI as well as related neurodegeneration and discuss the therapeutic potential of sirtuin modulators.