Acid sphingomyelinase deficiency protects mitochondria and improves function recovery after brain injury

Metabolic and Endocrine Dysfunctions in Traumatic Brain Injury: Implications for Cognitive Recovery and Therapeutic Strategies

Traumatic brain injury (TBI) triggers a chain reaction of intricate metabolic abnormalities, sometimes leading to ongoing cognitive deficits. These abnormalities comprise dysregulation in trace element homeostasis, disrupted neurotransmitter modulation, increased lipid peroxidation, compromised glucose metabolism, and organ-specific metabolic changes. Most recent studies suggest that metabolic abnormalities are the root cause of cognitive decline in post-traumatic stress disorder (TBI). Restoring metabolic balance through therapeutic modalities, such as antioxidant therapy to combat lipid peroxidation, glucose modulators to normalise cerebral energy metabolism, and trace element supplementation, shows promise. Furthermore, increasingly understood as important determinant of long-term neurocognitive outcomes are endocrine dysfunctions, especially post-traumatic hypopituitarism and growth hormone deficiency (GHD). Growth hormone replacement therapy has been shown to improve cognitive function and overall recovery. Biomarkers such as insulin-like growth factor-1 (IGF-1), neuroinflammatory cytokines (IL-6 and TNF-α), and oxidative stress markers (like malondialdehyde) can facilitate early diagnosis, which may allow for targeted and timely intervention. This review supports metabolism-oriented, biomarker-guided therapeutic approaches to improve neurocognitive recovery and patient quality of life, highlighting the critical role that metabolic and endocrine abnormalities play in post-TBI cognitive impairment.

Comparative lipid profiling reveals the differential response of distinct lipid subclasses in blast and blunt-induced mild traumatic brain injury

Head trauma from blast exposure is a growing health concern, particularly among active military personnel, and is considered the signature injury of the Gulf War. However, it remains elusive whether fundamental differences exist between blast-related Traumatic Brain Injuries (TBI) and TBI due to other mechanisms. Considering the importance of lipid metabolism associated with neuronal membrane integrity and its compromise during TBI, we sought to find changes in lipidomic profiling during blast or blunt (Stereotaxically Controlled Contusison-SCC)-mediated TBI. In the current study, we have developed the mild TBI (mTBI) model of blast (130 ± 10 kPa) and SCC (1.5 mm dorsal-ventral) on C57BL/6 mice, followed by the serum collection on days 1 and 7. Lipidomics was performed via ultra-high performance liquid chromatography (UHPLC) quadrupole time-of-flight mass spectrometry (qTOF-MS). Additionally, neurobehavioral outcomes were estimated using a revised neurobehavioral severity score for mice (mNSS-R) and an open field test (OFT). The study found that blast-exposed group exhibited more lipid dysregulation, as evidenced by a higher number of significant lipids and associated pathways at both time points. However, the comparative investigation further reveals eight significantly common lipids that can characterize the mTBI regardless of the manner of induction (blast or blunt). Besides, modulated neurobehavioral, locomotor and anxiety functions were also observed post-mTBI. The study illustrates the distinct systemic lipid metabolism intended to preserve the brain's lipid homeostasis post-mTBI. This approach may provide novel insights into lipid metabolism and identification of individual lipid species that aids in understanding the pathophysiology of mTBI.

Sphingolipid changes in mouse brain and plasma after mild traumatic brain injury at the acute phases

BACKGROUND

Traumatic brain injury (TBI) causes neuroinflammation and can lead to long-term neurological dysfunction, even in cases of mild TBI (mTBI). Despite the substantial burden of this disease, the management of TBI is precluded by an incomplete understanding of its cellular mechanisms. Sphingolipids (SPL) and their metabolites have emerged as key orchestrators of biological processes related to tissue injury, neuroinflammation, and inflammation resolution. No study so far has investigated comprehensive sphingolipid profile changes immediately following TBI in animal models or human cases. In this study, sphingolipid metabolite composition was examined during the acute phases in brain tissue and plasma of mice following mTBI.

METHODS

Wildtype mice were exposed to air-blast-mediated mTBI, with blast exposure set at 50-psi on the left cranium and 0-psi designated as Sham. Sphingolipid profile was analyzed in brain tissue and plasma during the acute phases of 1, 3, and 7 days post-TBI via liquid-chromatography-mass spectrometry. Simultaneously, gene expression of sphingolipid metabolic markers within brain tissue was analyzed using quantitative reverse transcription-polymerase chain reaction. Significance (P-values) was determined by non-parametric t-test (Mann-Whitney test) and by Tukey's correction for multiple comparisons.

RESULTS

In post-TBI brain tissue, there was a significant elevation of 1) acid sphingomyelinase (aSMase) at 1- and 3-days, 2) neutral sphingomyelinase (nSMase) at 7-days, 3) ceramide-1-phosphate levels at 1 day, and 4) monohexosylceramide (MHC) and sphingosine at 7-days. Among individual species, the study found an increase in C18:0 and a decrease in C24:1 ceramides (Cer) at 1 day; an increase in C20:0 MHC at 3 days; decrease in MHC C18:0 and increase in MHC C24:1, sphingomyelins (SM) C18:0, and C24:0 at 7 days. Moreover, many sphingolipid metabolic genes were elevated at 1 day, followed by a reduction at 3 days and an absence at 7-days post-TBI. In post-TBI plasma, there was 1) a significant reduction in Cer and MHC C22:0, and an increase in MHC C16:0 at 1 day; 2) a very significant increase in long-chain Cer C24:1 accompanied by significant decreases in Cer C24:0 and C22:0 in MHC and SM at 3 days; and 3) a significant increase of C22:0 in all classes of SPL (Cer, MHC and SM) as well as a decrease in Cer C24:1, MHC C24:1 and MHC C24:0 at 7 days.

CONCLUSIONS

Alterations in sphingolipid metabolite composition, particularly sphingomyelinases and short-chain ceramides, may contribute to the induction and regulation of neuroinflammatory events in the early stages of TBI, suggesting potential targets for novel diagnostic, prognostic, and therapeutic strategies in the future.

Acid sphingomyelinase as a pathological and therapeutic target in neurological disorders: focus on Alzheimer's disease

Over the past decade, numerous studies have highlighted the importance of acid sphingomyelinase (ASM) in disease treatment in humans. This enzyme functions primarily to generate ceramide, maintain the cellular membrane, and regulate cellular function. However, in the blood and brain of patients with neurological disorders, including major depression, ischemic stroke, amyotrophic lateral sclerosis, multiple sclerosis, and Alzheimer's disease (AD), elevated ASM levels significantly suggest disease onset or progression. In these diseases, increased ASM is profoundly involved in neuronal death, abnormal autophagy, neuroinflammation, blood-brain barrier disruption, hippocampal neurogenesis loss, and immune cell dysfunction. Moreover, genetic and pharmacological inhibition of ASM can prevent or ameliorate various diseases. The therapeutic effects of ASM inhibition have prompted the urgent need to develop ASM inhibitors, and several ASM inhibitors have been identified. In this review, we summarize the current knowledge on the critical roles and mechanisms of ASM in brain cells and blood that are associated with different neuropathological features, especially those observed in AD. Furthermore, we elucidate the potential possibility and limitations of existing ASM-targeting drugs according to experimental studies in neurological disorder mouse models.

Acid Sphingomyelinase Inhibitor, Imipramine, Reduces Hippocampal Neuronal Death after Traumatic Brain Injury

Traumatic brain injury (TBI) broadly degrades the normal function of the brain after a bump, blow, or jolt to the head. TBI leads to the aggravation of pre-existing brain dysfunction and promotes neurotoxic cascades that involve processes such as oxidative stress, loss of dendritic arborization, and zinc accumulation. Acid sphingomyelinase (ASMase) is an enzyme that hydrolyzes sphingomyelin to ceramide in cells. Under normal conditions, ceramide plays an important role in various physiological functions, such as differentiation and apoptosis. However, under pathological conditions, excessive ceramide production is toxic and activates the neuronal-death pathway. Therefore, we hypothesized that the inhibition of ASMase activity by imipramine would reduce ceramide formation and thus prevent TBI-induced neuronal death. To test our hypothesis, an ASMase inhibitor, imipramine (10 mg/kg, i.p.), was administrated to rats immediately after TBI. Based on the results of this study, we confirmed that imipramine significantly reduced ceramide formation, dendritic loss, oxidative stress, and neuronal death in the TBI-imipramine group compared with the TBI-vehicle group. Additionally, we validated that imipramine prevented TBI-induced cognitive dysfunction and the modified neurological severity score. Consequently, we suggest that ASMase inhibition may be a promising therapeutic strategy to reduce hippocampal neuronal death after TBI.

Brain Energy Metabolism: Astrocytes in Neurodegenerative Diseases

Astrocytes are the most abundant cells in the brain. They have many important functions in the central nervous system (CNS), including the maintenance of glutamate and ion homeostasis, the elimination of oxidative stress, energy storage in glycogen, tissue repair, regulating synaptic activity by releasing neurotransmitters, and participating in synaptic formation. Astrocytes have special highly ramified structure. Their branches contact with synapses of neurons inwardly, with fine structure and wrapping synapses; their feet contact with blood vessels of brain parenchyma outward, almost wrapping the whole brain. The adjacent astrocytes rarely overlap and communicate with each other through gap junction channels. The ideal location of astrocytes enables them to sense the weak changes of their surroundings and provide the structural basis for the energy supply of neurons. Neurons and astrocytes are closely coupled units of energy metabolism in the brain. Neurons consume a lot of ATPs in the process of neurotransmission. Astrocytes provide metabolic substrates for neurons, maintain high activity of neuron, and facilitate information transmission of neurons. This article reviews the characteristics of glucose metabolism, lipid metabolism, and amino acid metabolism of astrocytes. The metabolic interactions between astrocytes and neurons, astrocytes and microglia were also detailed discussed. Finally, we classified analyzed the role of metabolic disorder of astrocytes in the occurrence and development of neurodegenerative diseases.

Metabolic disorders on cognitive dysfunction after traumatic brain injury

Cognitive dysfunction is a common adverse consequence of traumatic brain injury (TBI). After brain injury, the brain and other organs trigger a series of complex metabolic changes, including reduced glucose metabolism, enhanced lipid peroxidation, disordered neurotransmitter secretion, and imbalanced trace element synthesis. In recent years, several research and clinical studies have demonstrated that brain metabolism directly or indirectly affects cognitive dysfunction after TBI, but the mechanisms remain unclear. Drugs that improve the symptoms of cognitive dysfunction caused by TBI are under investigation and treatments that target metabolic processes are expected to improve cognitive function in the future. This review explores the impact of metabolic disorders on cognitive dysfunction after TBI and provides new strategies for the treatment of metabolic disorders.

Early secretory pathway-resident Zn transporter proteins contribute to cellular sphingolipid metabolism through activation of sphingomyelin phosphodiesterase 1

Sphingomyelin phosphodiesterase 1 (SMPD1) converts sphingomyelin into ceramide and phosphocholine; hence, loss of SMPD1 function causes abnormal accumulation of sphingomyelin in lysosomes, which results in the lipid-storage disorder Niemann-Pick disease (types A and B). SMPD1 activity is dependent on zinc, which is coordinated at the active site of the enzyme, and although SMPD1 has been suggested to acquire zinc at the sites where the enzyme is localized, precisely how SMPD1 acquires zinc remains to be clarified. Here, we addressed this using a gene-disruption/re-expression strategy. Our results revealed that Zn transporter 5 (ZNT5)-ZNT6 heterodimers and ZNT7 homodimers, which localize in the compartments of the early secretory pathway, play essential roles in SMPD1 activation. Both ZNT complexes contribute to cellular sphingolipid metabolism by activating SMPD1 because cells lacking the functions of the two complexes exhibited a reduced ceramide to sphingomyelin content ratio in terms of their dominant molecular species and an increase in the sphingomyelin content in terms of three minor species. Moreover, mutant cells contained multilamellar body-like structures, indicative of membrane stacking and accumulation, in the cytoplasm. These findings provide novel insights into the molecular mechanism underlying the activation of SMPD1, a key enzyme in sphingolipid metabolism.

Systemic Elevation of n-3 Polyunsaturated Fatty Acids (n-3-PUFA) Is Associated with Protection against Visual, Motor, and Emotional Deficits in Mice following Closed-Head Mild Traumatic Brain Injury

Traumatic brain injury (TBI) causes neuroinflammation and neurodegeneration leading to various pathological complications such as motor and sensory (visual) deficits, cognitive impairment, and depression. N-3 polyunsaturated fatty acid (n-3 PUFA) containing lipids are known to be anti-inflammatory, whereas the sphingolipid, ceramide (Cer), is an inducer of neuroinflammation and degeneration. Using Fat1+-transgenic mice that contain elevated levels of systemic n-3 PUFA, we tested whether they are resistant to mild TBI-mediated sensory-motor and emotional deficits by subjecting Fat1-transgenic mice and their WT littermates to focal cranial air blast (50 psi) or sham blast (0 psi, control). We observed that visual function in WT mice was reduced significantly following TBI but not in Fat1+-blast animals. We also found Fat1+-blast mice were resistant to the decline in motor functions, depression, and fear-producing effects of blast, as well as the reduction in the area of oculomotor nucleus and increase in activated microglia in the optic tract in brain sections seen following blast in WT mice. Lipid and gene expression analyses confirmed an elevated level of the n-3 PUFA eicosapentaenoic acid (EPA) in the plasma and brain, blocking of TBI-mediated increase of Cer in the brain, and decrease in TBI-mediated induction of Cer biosynthetic and inflammatory gene expression in the brain of the Fat1+ mice. Our results demonstrate that suppression of ceramide biosynthesis and inflammatory factors in Fat1+-transgenic mice is associated with significant protection against the visual, motor, and emotional deficits caused by mild TBI. This study suggests that n-3 PUFA (especially, EPA) has a promising therapeutic role in preventing neurodegeneration after TBI.

Methylprednisolone Induces Neuro-Protective Effects via the Inhibition of A1 Astrocyte Activation in Traumatic Spinal Cord Injury Mouse Models

Traumatic spinal cord injury (TSCI) leads to pathological changes such as inflammation, edema, and neuronal apoptosis. Methylprednisolone (MP) is a glucocorticoid that has a variety of beneficial effects, including decreasing inflammation and ischemic reaction, as well as inhibiting lipid peroxidation. However, the efficacy and mechanism of MP in TSCI therapy is yet to be deciphered. In the present study, MP significantly attenuated the apoptotic effects of H₂O₂ in neuronal cells. Western blot analysis demonstrated that the levels of apoptotic related proteins, Bax and cleaved caspase-3, were reduced while levels of anti-apoptotic Bcl-2 were increased. In vivo TUNEL assays further demonstrated that MP effectively protected neuronal cells from apoptosis after TSCI, and was consistent with in vitro studies. Furthermore, we demonstrated that MP could decrease expression levels of IBA1, Il-1α, TNFα, and C3 and suppress A1 neurotoxic reactive astrocyte activation in TSCI mouse models. Neurological function was evaluated using the Basso Mouse Scale (BMS) and Footprint Test. Results demonstrated that the neurological function of MP-treated injured mice was significantly increased. In conclusion, our study demonstrated that MP could attenuate astrocyte cell death, decrease microglia activation, suppress A1 astrocytes activation, and promote functional recovery after acute TSCI in mouse models.

Inhibition of extracellular vesicle pathway using neutral sphingomyelinase inhibitors as a neuroprotective treatment for brain injury

Traumatic brain injury is a sudden trauma or blow on the head, and severe traumatic brain injury is a major cause of death and disability worldwide. The acute and chronic consequences following traumatic brain injury can lead to progressive secondary neurodegenerative changes and cognitive dysfunction. To date, there is no effective pharmaceutical products for the treatment to reduce secondary damage after brain injury. The discovery of extracellular vesicles has attracted considerable scientific attention due to their role in cell-to-cell communication. Extracellular vesicles have shown their potential to carry not only biological molecules but also as a drug delivery vehicle. As a carrier of molecular information, extracellular vesicles have been involved in physiological functions as well as in the modulation of immune responses. Here, we aim to provide new insights into the contrasting role of extracellular vesicles in the propagation of inflammatory responses after brain injury. As a carrier of pro-inflammatory molecules, their role as functional mediators in the pathophysiology of brain injury is discussed, addressing the inhibition of the extracellular vesicle pathway as an anti-inflammatory or neuroprotective approach to improve the outcome of both acute and chronic inflammation following brain injury. Here, we summarize therapeutic strategies to diminish the risk the neurodegeneration post brain injury and propose that neutral sphingomyelinase inhibitors could be used as potentially useful therapeutic agents for the treatment of brain injury associated neuroinflammation.

Lipid metabolism in astrocytic structure and function

Astrocytes are the most abundant glial cell in the central nervous system and are involved in multiple processes including metabolic homeostasis, blood brain barrier regulation and neuronal crosstalk. Astrocytes are the main storage point of glycogen in the brain and it is well established that astrocyte uptake of glutamate and release of lactate prevents neuronal excitability and supports neuronal metabolic function. However, the role of lipid metabolism in astrocytes in relation to neuronal support has been until recently, unclear. Lipids play a fundamental role in astrocyte function, including energy generation, membrane fluidity and cell to cell signaling. There is now emerging evidence that astrocyte storage of lipids in droplets has a crucial physiological and protective role in the central nervous system. This pathway links β-oxidation in astrocytes to inflammation, signalling, oxidative stress and mitochondrial energy generation in neurons. Disruption in lipid metabolism, structure and signalling in astrocytes can lead to pathogenic mechanisms associated with a range of neurological disorders.

Ferroptosis-relevant mechanisms and biomarkers for therapeutic interventions in traumatic brain injury

Traumatic brain injury (TBI) is one of the most significant health care problems worldwide, causing disability and death especially among young individuals. Although a large range of agents and therapies have been proved beneficial to lesions post-TBI to some extent, effective treatments have not been translated to the clinic. As a newly discovered form of iron-dependent regulated cell death, ferroptosis has been implicated in TBI. In this review, we update the current state of knowledge related to second injuries post-TBI, including ferroptosis, oxidative stress, mitochondrial dysfunction, neuroinflammation and so on, which often lead to chronic symptoms and long-term disability. This review systematically summarizes the latest progress in the pathophysiological mechanisms of TBI, with a focus on providing references for proposing new multi-molecular targets for comprehensive therapeutic strategies based on ferroptosis-relevant mechanisms. In addition, biomarkers are essential diagnostic and prognostic tools in TBI. Several biomarkers associated with the outcome of TBI have been listed in this article, such as Pde10a, MDA, UCH-L1, S100A9, S100B, ALDOC, ACSL4, MBP and F2-Isoprostane. Therefore, the understating of ferroptosis-relevant mechanisms and biomarkers may contribute to development of promising therapies for TBI clinical trials.

Crosstalk Between Acid Sphingomyelinase and Inflammasome Signaling and Their Emerging Roles in Tissue Injury and Fibrosis

Inflammasomes are a group of protein complexes that are assembled by pattern recognition receptors following the recognition of invading pathogens or host-derived danger signals. Inflammasomes such as NLRP3 mediate the activation of caspase-1 and the production of the proinflammatory cytokines IL-18 and IL-1β. Regulation of inflammasome signaling is critical for host defense against infections and maintenance of cellular homeostasis upon exposure to multiple harmful stimuli. Recent studies have highlighted an important role of acid sphingomyelinase (ASM) in regulating inflammasome activation. ASM hydrolyzes sphingomyelin to ceramide, which further fuses to large ceramide-enriched platforms functioning in stabilizing and amplifying molecules and receptors. Here, we will discuss the current understanding of the ASM-ceramide system in inflammasome activation, and how it contributes to multiple diseases. Insights into such mechanisms would pave the way for further exploration of novel diagnostic, preventative, and therapeutic targets against tissue injury and fibrosis.

Acid sphingomyelinase deficiency exacerbates LPS-induced experimental periodontitis

BACKGROUND

Mutation of the gene for acid sphingomyelinase (ASMase) causes Niemann-Pick disease. However, the effect of ASMase deficiency on periodontal health is unknown. Periodontal disease is a disease resulting from infection and inflammation of periodontal tissue and alveolar bone that support the teeth. The goal of this study was to determine the role of ASMase deficiency in periodontal inflammation and alveolar bone loss.

METHODS

We induced periodontitis in wild-type and ASMase-deficient (ASMase^-/- ) mice with periodontal lipopolysaccharide (LPS) injection and compared the alveolar bone loss and periodontal inflammation between these mice.

RESULTS

Results showed that ASMase deficiency did not significantly change metabolic parameters, but exacerbated LPS-induced alveolar bone loss, osteoclastogenesis, and periodontal tissue inflammation. To understand the mechanisms by which ASMase deficiency aggravates LPS-induced periodontitis, we analyzed sphingolipids in periodontal tissues. Results showed that ASMase deficiency led to increases in not only sphingomyelin, but also ceramide (CER), a bioactive sphingolipid known to promote inflammation. Results further showed that ASMase deficiency increased CER de novo synthesis.

CONCLUSION

ASMase deficiency exacerbated LPS-induced alveolar bone loss and periodontal inflammation. ASMase deficiency leads to an unexpected CER increase by stimulating de novo synthesis CER, which is likely to be involved in the ASMase deficiency-exacerbated periodontitis.