Peethambaran Arun

Background: Blast-induced spinal cord injuries (bSCI) account for 75% of all combat-related spinal trauma and are associated with long-term functional impairments. However, limited studies have evaluated the neuropathological outcomes in the spinal cord following blast exposure. Objectives In this study, we aimed to determine the acute and sub-acute neuropathological changes in the spinal cord of ferrets after blast exposure. Methods: An advanced blast simulator was used to expose ferrets to tightly coupled repeated blasts. The Catwalk XT system was used to detect gait performances in ferrets at 24 h and 1 month post-blast exposure. After euthanasia, the cervical spinal cord samples were collected at 24 h or 1 month post-blast. A quantitative real-time polymerase chain reaction was performed to evaluate changes in the gene expression of multiple Toll-like Receptors (TLR), Cyclooxygenase (COX-1 and COX-2) enzymes and cytokines. Western blotting was performed to investigate markers of axonal injury (Phosphorylated-Tau, pTau; Phosphorylated Neurofilament Heavy Chain, pNFH; and Neurofilament Light Chain present in degenerating neurons, NFL-degen) and neuroinflammation (Glial Fibrillary Acidic Protein, GFAP; and Ionized Calcium Binding Adaptor Molecule, Iba-1). Results: Blast exposure significantly affected the gait performances in ferrets, especially at 24 h post-blast. Multiple TLRs, COX-2, Interleukin-1-beta (IL-1β), Interleukin-6 (IL-6), and Tumor Necrosis Factor-α (TNF-α) were significantly upregulated in the spinal cord at 24 h after blast exposure. Although only TLR3 was significantly upregulated at 1 month, non-significant increases in TLR1 and TLR2 were observed in the spinal cord at 1 month post-blast. Phosphorylation of Tau at serine (Ser396 and Ser404) and threonine (Thr205) increased in the spinal cord at 24 h and 1 month post-blast exposure. The increased expression of pNFH and NFL-degen proteins was evident at both time points. The expression of GFAP, but not Iba-1, significantly increased at 24 h and 1 month following blast exposure. Conclusions: Our results indicate that blast exposure causes acute and sub-acute neuroinflammation and associated axonal injury in the cervical spinal cord. These data further suggest that inhibition of TLRs and/or COX-2 enzyme might offer protection against blast-induced injuries to the spinal cord.

Traumatic brain injury (TBI) remains a significant public health concern, particularly among military personnel and contact sport athletes who are frequently exposed to repeated blast overpressure waves and mild concussive impacts, respectively. While moderate and severe TBIs have been extensively studied, the long-term neuroendocrine consequences of mild, repetitive brain trauma are poorly understood. In this study, we investigated the temporal dynamics of hypothalamic–pituitary–adrenal (HPA) axis dysregulation following repeated mild concussive head impacts and blast exposures using two clinically relevant rodent models. Male Sprague-Dawley rats were subjected to repeated mild concussive impacts using a modified weight drop model or repeated blast exposures using an advanced blast simulator. Plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone were measured on days 1 and 30 post-injuries. Our findings revealed that repeated blast exposures induced elevation of plasma ACTH and corticosterone on days 1 and 30 post-blasts. After the repeated mild concussive impacts, increased plasma levels of corticosterone were observed on days 1 and 30, but ACTH levels were increased only on day 30. This study is among the first to directly compare neuroendocrine outcomes of repeated mild concussive impacts and blast exposures within a unified experimental framework. Our findings demonstrate distinct temporal trajectories of HPA axis dysregulation depending on injury type and highlight plasma levels of ACTH and corticosterone as potential biomarkers of subclinical brain trauma. These insights may inform early diagnostic approaches and therapeutic strategies aimed at mitigating long-term stress-related complications following mild traumatic brain injuries.

Blast-induced polytrauma (BIPT) is a common injury among military personnel exposed to explosive blasts. It is increasingly recognized as a complex, multisystem disorder that extends beyond neurological damage to include systemic metabolic and inflammatory dysfunction. Adipokines, particularly leptin and adiponectin, are hormones secreted by adipose tissue and are emerging as key mediators in the pathophysiology of traumatic brain injuries. Yet, their long-term dynamics following blast exposure remain unclear. This study investigated the temporal profiles of plasma leptin and adiponectin in a longitudinal rat model of BIPT. Adult male Sprague Dawley rats were subjected to either a single (B) or repeated (BB) blast exposure (20 psi) or served as sham controls. Plasma samples were collected at 24 h, 1 month, 6 months, and 12 months post-exposure, and adipokine levels were measured using Enzyme-linked Immunosorbent Assay. Adiponectin levels exhibited a biphasic response: both B and BB groups showed significant early decrease at 24 h and 1 month compared to sham animals, followed by robust elevation at 6 and 12 months, particularly in the repeated blast group. In contrast, leptin levels remained unchanged acutely but rose significantly at 6 and 12 months post-blast, with the BB group again showing the highest levels. These patterns indicate sustained, exposure-dependent dysregulation of adipokine signaling after blast trauma. The study provides the first longitudinal profile of systemic adipokine responses to BIPT, revealing their potential as accessible biomarkers and therapeutic targets. These findings support a model of chronic metabolic and inflammatory imbalance in BIPT and warrant further investigation in human cohorts and mechanistic studies.

Background/Objectives: Blast-induced traumatic ocular injuries (bTOI) pose a significant risk to military and civilian populations, often leading to visual impairment or blindness. Retina, the innermost layer of ocular tissue consisting of photoreceptor and glial cells, is highly susceptible to blast injuries. Despite its prevalence, the molecular mechanisms underlying retinal damage following bTOI remain poorly understood, hindering the development of targeted therapies. Melatonin, a neuroprotective indoleamine with antioxidant, anti-inflammatory, and circadian regulatory properties, is synthesized in the retina and plays a crucial role in retinal health. Similarly, retina-specific genes, such as Rhodopsin, Melanopsin, and RPE65, are essential for photoreceptor function, visual signaling, and the visual cycle. However, their responses to blast exposure have not been thoroughly investigated. Methods: In this study, we utilized a ferret model of bTOI to evaluate the temporal expression of melatonin-synthesizing enzymes, such as tryptophan hydroxylase 1 and 2 (TPH1 and TPH2), Aralkylamine N-acetyltransferase (AANAT), and Acetylserotonin-O-methyltransferase (ASMT), and retina-specific genes (Rhodopsin, Melanopsin) and retinal pigment epithelium-specific 65 kDa protein (RPE65) at 4 h, 24 h, 7 days, and 28 days post-blast. Ferrets were exposed to tightly coupled blast overpressure waves using an advanced blast simulator, and retinal tissues were collected for quantitative polymerase chain reaction (qPCR) analysis. Results: The results revealed dynamic and multiphasic transcriptional responses. TPH1 and TPH2 exhibited significant upregulation at 24 h, followed by downregulation at 28 days, indicating blast-induced dysregulation of tryptophan metabolism, including melatonin synthesis. Similarly, AANAT and ASMT showed acute downregulation post-blast, with late-phase disruptions. Rhodopsin expression increased at 24 h but declined at 28 days, while Melanopsin and RPE65 demonstrated early upregulation followed by downregulation, reflecting potential disruptions in circadian regulation and the visual cycle. Conclusions: These findings highlight the complex regulatory mechanisms underlying retinal responses to bTOI, involving neuroinflammation, oxidative stress, and disruptions in melatonin synthesis and photoreceptor cell functions. The results emphasize the therapeutic potential of melatonin in mitigating retinal damage and preserving visual function.

Mild concussive events without loss of consciousness are typically left untreated and can result in neurological abnormalities at later stages of life. No systematic studies have been carried out to determine the effect of concussion or repeated mild concussive episodes on brain vulnerability towards blast exposure. We have evaluated the effect of repeated mild concussive events on the vulnerability of brain to blast exposure using neurobehavioral functional assessments. Rats were subjected to either repeated mild concussive impacts (two impacts 1 week apart using a modified Marmarou weight drop model), a single blast exposure (19 psi using an advanced blast simulator), or a single blast exposure one day after the second mild concussive impact. Neurobehavioral changes were monitored using rotating pole test, open field exploration test, and novel object recognition test. Rotating pole test results indicated that vestibulomotor function was unaffected by blast or repeated mild concussive impacts, but significant impairment was observed in the blast exposed animals who had prior repeated mild concussive impacts. Novel object recognition test revealed short-term memory loss at 1 month post-blast only in rats subjected to both repeated mild concussive impacts and blast. Horizontal activity count, ambulatory activity count, center time and margin time legacies in the open field exploratory activity test indicated that only those rats exposed to both repeated mild concussive impacts and blast develop anxiety-like behaviors at both acute and sub-acute time-points. The results indicate that a history of repeated mild concussive episodes heightens brain vulnerability to blast exposure.

Blast-induced traumatic brain injury (bTBI) has been identified as the signature injury of Operation Iraqi Freedom and Operation Enduring Freedom. Although the incidence of bTBI increased significantly after the introduction of improvised explosive devices, the mechanism of the injury is still uncertain, which is negatively impacting the development of suitable countermeasures. Identification of suitable biomarkers that could aid in the proper diagnosis of and prognosis for both acute and chronic bTBI is essential since bTBI frequently is occult and may not be associated with overtly detectable injuries to the head. Lysophosphatidic acid (LPA) is a bioactive phospholipid generated by activated platelets, astrocytes, choroidal plexus cells and microglia and is reported to play major roles in stimulating inflammatory processes. The levels of LPA in the cerebrospinal fluid (CSF) have been reported to increase acutely after non-blast related brain injuries. In the present study, we have evaluated the utility of LPA levels measured in the CSF and plasma of laboratory rats as an acute and chronic biomarker of brain injury resulting from single and tightly coupled repeated blast overpressure exposures. In the CSF, many LPA species increased at acute time-points, returned to normal levels at 1 month, and increased again at 6 months and 1 year post-blast overpressure exposures. In the plasma, several LPA species increased acutely, returned to normal levels by 24 h, and were significantly decreased at 1 year post-blast overpressure exposures. These decreases in LPA species in the plasma were associated with decreased levels of lysophosphatidyl choline, suggesting a defective upstream biosynthetic pathway of LPAs in the plasma. Notably, the changes in LPA levels in the CSF (but not plasma) negatively correlated with neurobehavioral functions in these rats, suggesting that CSF levels of LPAs may provide a suitable biomarker of bTBI that reflects severity of injury.

Blast-induced traumatic brain injury (bTBI) frequently results in sleep and circadian rhythm disturbances. We have investigated whether dysregulation of circadian rhythm after bTBI is mediated by dysregulation of clock genes in the hypothalamus and pineal gland of rats at acute (24 h) and chronic (1 month) time points post-blast. Expression of core circadian genes ( Bmal1 , Clock , Per1 , Per2 , Cry1 , and Cry2 ) in the hypothalamus and pineal gland were quantified using quantitative real-time polymerase chain reaction. Hypocretin ( Hcrt ) and hypocretin receptor ( Hcrtr1 and Hcrtr2 ) expression in the hypothalamus were also quantified along with plasma corticosterone levels. Blast-exposed rats showed a statistically significant increase in Bmal1 and decreases in Per1 , Per2 , and Cry2 in the pineal gland at 24 h post-blast in rats euthanized at night. In the hypothalamus, increases in Bmal1 , Cry1 , and Cry2 were noted along with decreases in Per1 and Per2 gene expression at 24 h post-blast in rats euthanized at night. Except for Bmal1 in the hypothalamus, no statistically significant changes in expression of any of the clock genes were detected in the hypothalamus or pineal gland samples collected during daylight post-blast. In the hypothalamus, a decrease in Hcrt associated with increases in Hcrtr1 and Hcrtr2 were noted at 24 h post-blast in rats euthanized during daytime and nighttime. Increased plasma corticosterone was noted at 24 h post-blast in samples collected at night. No statistically significant changes in any of the core circadian genes—hypocretin, hypocretin receptors, or plasma corticosterone—were observed in the samples collected at 1 month post-blast injury. Blast exposure causes differential expression of core circadian genes in the hypothalamus and pineal gland during nighttime, along with dysregulation of hypocretin and its receptors, which might play a key role in the sleep disruptions associated with bTBI.

The coordination of cellular biological processes is regulated in part via metabolic enzymes acting to match cellular metabolism to current conditions. The acetate activating enzyme, acyl-coenzyme A synthetase short-chain family member 2 (Acss2), has long been considered to have a predominantly lipogenic function. More recent evidence suggests that this enzyme has regulatory functions in addition to its role in providing acetyl-CoA for lipid synthesis. We used Acss2 knockout mice (Acss2^−/−) to further investigate the roles this enzyme plays in three physiologically distinct organ systems that make extensive use of lipid synthesis and storage, including the liver, brain, and adipose tissue. We examined the resulting transcriptomic changes resulting from Acss2 deletion and assessed these changes in relation to fatty acid constitution. We find that loss of Acss2 leads to dysregulation of numerous canonical signaling pathways, upstream transcriptional regulatory molecules, cellular processes, and biological functions, which were distinct in the liver, brain, and mesenteric adipose tissues. The detected organ-specific transcriptional regulatory patterns reflect the complementary functional roles of these organ systems within the context of systemic physiology. While alterations in transcriptional states were evident, the loss of Acss2 resulted in few changes in fatty acid constitution in all three organ systems. Overall, we demonstrate that Acss2 loss institutes organ-specific transcriptional regulatory patterns reflecting the complementary functional roles of these organ systems. Collectively, these findings provide further confirmation that Acss2 regulates key transcription factors and pathways under well-fed, non-stressed conditions and acts as a transcriptional regulatory enzyme.

Coordination of cellular biological processes is regulated in part via metabolic enzymes acting to match cellular metabolism to current conditions. The acetate activating enzyme, acyl-coenzyme A synthetase short-chain family member 2 (Acss2) has long been considered to have a predominantly lipogenic function. More recent evidence suggests that this enzyme has regulatory functions in addition to its role in providing acetyl-CoA for lipid synthesis. We used Acss2 knockout mice (Acss2-/-) to further investigate the roles this enzyme plays in three physiologically distinct organ systems that make extensive use of lipid synthesis and storage including the liver, brain and adipose tissue. We examined the resulting transcriptomic changes resulting from Acss2 deletion and assessed these changes in relation to fatty acid constitution. We find that loss of Acss2 leads to dysregulation of numerous canonical signaling pathways, upstream transcriptional regulatory molecules, cellular processes, and biological functions, which were distinct in the liver, brain and mesenteric adipose tissues. The detected organ-specific transcriptional regulatory patterns reflect the complementary functional roles of these organ systems within the context of systemic physiology. While alterations in transcriptional states were evident, the loss of Acss2 resulted in few changes in fatty acid constitution in all three organ systems. Overall, we demonstrate Acss2 loss institutes organ-specific transcriptional regulatory patterns reflecting the complementary functional roles of these organ systems. Collectively, these findings provide further confirmation that Acss2 regulates key transcription factors and pathways under well-fed, non-stressed conditions, and acts as a transcriptional regulatory enzyme.