Neurogranin Protein Expression Is Reduced after Controlled Cortical Impact in Rats

Temporal-Specific Sex and Injury-Dependent Changes on Neurogranin-Associated Synaptic Signaling After Controlled Cortical Impact in Rats

Extensive effort has been made to study the role of synaptic deficits in cognitive impairment after traumatic brain injury (TBI). Neurogranin (Ng) is a calcium-sensitive calmodulin (CaM)-binding protein essential for Ca2+/CaM-dependent kinase II (CaMKII) autophosphorylation which subsequently modulates synaptic plasticity. Given the loss of Ng expression after injury, additional research is warranted to discern changes in hippocampal post-synaptic signaling after TBI. Under isoflurane anesthesia, adult, male and female Sprague-Dawley rats received a sham/control or controlled cortical impact (CCI) injury. Ipsilateral hippocampal synaptosomes were isolated at 24 h and 1, 2, and 4 weeks post-injury, and western blot was used to evaluate protein expression of Ng-associated signaling proteins. Non-parametric Mann-Whitney tests were used to determine significance of injury for each sex at each time point. There were significant changes in the hippocampal synaptic expression of Ng and associated synaptic proteins such as phosphorylated Ng, CaMKII, and CaM up to 4 weeks post-CCI, demonstrating TBI alters hippocampal post-synaptic signaling. This study furthers our understanding of mechanisms of cognitive dysfunction within the synapse sub-acutely after TBI.

Molecular Characterization of Neurogranin (NRGN) Gene from Red‑Bellied Pacu (Piaractus brachypomus)

Neurogranin (NRGN) is a small brain protein expressed in various telencephalic areas and plays an essential role in synaptic plasticity by regulating the availability of calmodulin (CaM). The study aims to characterize the neurogranin gene in Colombian native fish, red-bellied pacu, Piaractus brachypomus, its basal tissue expression and differential expression in brain injury and sublethal toxicity by organophosphates. NRGN gene contains an open reading frame of 183 nucleotides encoding for 60 amino acids. Bioinformatics analysis showed an IQ motif necessary in the interaction with CaM. NRGN mRNA was detected in tissues with higher expression in brain, gills, and head kidney. In brain regions, NRGN showed high expression in the telencephalon (TE) and olfactory bulb (OB). In the sublethal toxicity experiment, NRGN mRNA was upregulated in individuals under organophosphate exposure in the OB and optic chiasm (OC). In brain injury experiment, NRGN showed upregulation at 14 days in OC and at 24 h and 7 days in TE. These findings demonstrate the differential expression of NRGN under different experimental conditions which make it a candidate for a biomarker in the brain of P. brachypomus.

A role for protein arginine methyltransferase 7 in repetitive and mild traumatic brain injury

Mild traumatic brain injury affects the largest proportion of individuals in the United States and world-wide. Pre-clinical studies of repetitive and mild traumatic brain injury (rmTBI) have been limited in their ability to recapitulate human pathology (i.e. diffuse rotational injury). We used the closed-head impact model of engineered rotation acceleration (CHIMERA) to simulate rotational injury observed in patients and to study the pathological outcomes post-rmTBI using C57BL/6J mice. Enhanced cytokine production was observed in both the cortex and hippocampus to suggest neuroinflammation. Furthermore, microglia were assessed via enhanced iba1 protein levels and morphological changes using immunofluorescence. In addition, LC/MS analyses revealed excess glutamate production, as well as diffuse axonal injury via Bielschowsky's silver stain kit. Moreover, the heterogeneous nature of rmTBI has made it challenging to identify drug therapies that address rmTBI, therefore we sought to identify novel targets in the concurrent rmTBI pathology. The pathophysiological findings correlated with a time-dependent decrease in protein arginine methyltransferase 7 (PRMT7) protein expression and activity post-rmTBI along with dysregulation of PRMT upstream mediators s-adenosylmethionine and methionine adenosyltransferase 2 (MAT2) in vivo. In addition, inhibition of the upstream mediator MAT2A using the HT22 hippocampal neuronal cell line suggest a mechanistic role for PRMT7 via MAT2A in vitro. Collectively, we have identified PRMT7 as a novel target in rmTBI pathology in vivo and a mechanistic link between PRMT7 and upstream mediator MAT2A in vitro.

The diagnostic and prognostic value of serum neurogranin in acute ischemic stroke

OBJECTIVES

Stroke is a frequently encountered life-threatening medical condition in emergency departments (EDs). Despite all worldwide efforts, a reliable circulating biomarker has not been identified yet. This study investigates the diagnostic and prognostic value of neurogranin (Ng) in acute ischemic stroke (AIS).

METHODS

This prospective case-control study was conducted on ED patients with AIS and healthy volunteers. We collected the basic demographics, measured serum Ng levels of the patients vs. controls, and followed up the patient group for 6-month by phone or clinical notes to assess the functional outcomes.

RESULTS

Data analysis was completed with 142 subjects (86 patients vs. 55 controls). The groups did not differ in terms of age and gender. The median serum Ng level of the patient group was significantly higher compared to the control group [160.00 (75.93) vs. 121.26 (90.35) ng/mL and p ˂ 0.001, respectively]. Serum Ng level of 25 patients admitted to the ED within the first 6 hours from the onset of AIS was 177.93 (24.03) ng/mL, while serum Ng level of 61 patients admitted to the ED within 6-24 hours was 131.84 (76.44) ng/mL. AUROC results were 0.717 vs. 0.868 vs. 0.874 for stroke patients admitted during the first 24 hours, 6 hours, and 4.5 hours after the onset, respectively. Lesion volume, NIHSS, and modified Rankin Scale scores (mRS) at admission showed no significant correlation with Ng levels as well as 6-month mortality and 6-month mRS.

CONCLUSIONS

Timely AIS diagnosis is still a challenge for emergency departments due to the dependency on imaging. Serum Ng can be a promising diagnostic biomarker for AIS patients admitted in the first 24 hours. Even it outperformed in the first 4.5 and 6-hour time windows. However, it did not show a significant prognostic value.

Assessment of behavioral, neuroinflammatory, and histological responses in a model of rat repetitive mild fluid percussion injury at 2 weeks post-injury

Repetitive mild traumatic brain injury (rmTBI) is a prominent public health concern, with linkage to debilitating chronic sequelae. Developing reliable and well-characterized preclinical models of rmTBI is imperative in the investigation of the underlying pathophysiological mechanisms, as models can have varying parameters, affecting the overall pathology of the resulting injury. The lateral fluid percussion injury (FPI) model is a reliable and frequently used method of TBI replication in rodent subjects, though it is currently relatively underutilized in rmTBI research. In this study, we have performed a novel description of a variation of the lateral repetitive mild FPI (rmFPI) model, showing the graded acute behavioral impairment and histopathology occurring in response to one, two or four mild FPI (1.25 atm) or sham surgeries, implemented 24h apart. Beam walking performance revealed significant motor impairment in injured animals, with dysfunction increasing with additional injury. Based upon behavioral responses and histological observations, we further investigated the subacute pathophysiological outcomes of the dual FPI (dFPI). Immunoreactivity assessments showed that dFPI led to regionally-specific reductions in the post-synaptic protein neurogranin and increased subcortical white matter staining of the presynaptic protein synaptophysin at 2 weeks following dFPI. Immunohistochemical assessments of the microglial marker Iba-1 showed a striking increase in in several brain regions, and assessment of the astrocytic marker GFAP showed significantly increased immunoreactivity in the subcortical white matter and thalamus. With this study, we have provided a novel account of the subacute post injury outcomes occurring in response to a rmFPI utilizing these injury and frequency parameters, and thereby also demonstrating the reliability of the lateral FPI model in rmTBI replication.

Analysis of the risk of traumatic brain injury and evaluation neurogranin and myelin basic protein as potential biomarkers of traumatic brain injury in postmortem examination

In forensic pathology, traumatic brain injury (TBI) is a frequently encountered cause of death. Unfortunately, the statistic autopsy data, risk investigation about injury patterns, and circumstances of TBI are still sparse. Estimates of survival time post-TBI and postmortem diagnosis of TBI are especially important implications in forensic medicine. Neurogranin (Ng) and myelin basic protein (MBP) represent potential biomarkers of TBI. The present study analyzed retrospectively the forensic autopsy records of TBI cases at a university center of medico-legal investigation from 2008 to 2020. Immunohistochemistry and enzyme-linked immunosorbent assays (ELISA) were used to investigate the expression changes of Ng and MBP in the cortical brain injury adjacent tissues and serum, respectively, from cases of TBI at autopsy with different survival times post-TBI. The results show that the major mechanism of death of TBI is assault, and accident was the major manner of death. Ng and MBP are mainly expressed in the cortical nerve cells and the myelin sheath, respectively. The serum levels of Ng and MBP in each TBI group were higher compared with those in the controls. The brain cortical levels of Ng and MBP decreased at first and then steadily increased with extended survival time post-TBI. The immunopositive ratios and serum concentration of Ng and MBP have shown significant differences among control group and all TBI group (p < 0.001). Collectively, the immunohistochemical analyses of Ng and MBP in human brain tissues may be useful to determine the survival time after TBI, and Ng and MBP level in the human blood specimens could be considered as a postmortem diagnostic tools of TBI in forensic practice.

All-trans Retinoic Acid has Limited Therapeutic Effects on Cognition and Hippocampal Protein Expression After Controlled Cortical Impact

Traumatic brain injury (TBI) is known to impair synaptic function, and subsequently contribute to observed cognitive deficits. Retinoic Acid (RA) signaling modulates expression of synaptic plasticity proteins and is involved in hippocampal learning and memory. All trans-retinoic acid (ATRA), a metabolite of Vitamin A, has been identified as a potential pharmacotherapeutic for other neurological disorders due to this role. This study conducted an ATRA dose response to determine its therapeutic effects on cognitive behaviors and expression of hippocampal markers of synaptic plasticity and RA signaling proteins after experimental TBI. Under isoflurane anesthesia, adult male Sprague Dawley rats received either controlled cortical impact (CCI, 2.5 mm deformation, 4 m/s) or control surgery. Animals received daily intraperitoneal injection of 0.5, 1, 5, or 10 mg/kg of ATRA or vehicle for 2 weeks. Animals underwent motor and spatial learning and memory testing. Hippocampal expression of synaptic plasticity proteins neurogranin (Ng), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 sub-unit, as well as RA signaling proteins STRA6, ADLH1a1, CYP26A1 and CYP26B1 were evaluated by western blot at 2-weeks post-injury. ATRA treatment significantly recovered Ng synaptic protein expression, while having no effect on motor performance, spatial learning, and memory, and GluA1 expression after TBI. RA signaling protein expression is unchanged 2 weeks after TBI. Overall, ATRA administration after TBI showed limited therapeutic benefits compared to the vehicle.

A role for insulin-like growth factor-1 in hippocampal plasticity following traumatic brain injury

Traumatic brain injury (TBI) initiates a constellation of secondary injury cascades, leading to neuronal damage and dysfunction that is often beyond the scope of endogenous repair mechanisms. Cognitive deficits are among the most persistent morbidities resulting from TBI, necessitating a greater understanding of mechanisms of posttraumatic hippocampal damage and neuroplasticity and identification of therapies that improve recovery by enhancing repair pathways. Focusing here on hippocampal neuropathology associated with contusion-type TBIs, the impact of brain trauma on synaptic structure and function and the process of adult neurogenesis is discussed, reviewing initial patterns of damage as well as evidence for spontaneous recovery. A case is made that insulin-like growth factor-1 (IGF-1), a growth-promoting peptide synthesized in both the brain and the periphery, is well suited to augment neuroplasticity in the injured brain. Essential during brain development, multiple lines of evidence delineate roles in the adult brain for IGF-1 in the maintenance of synapses, regulation of neurotransmission, and modulation of forms of synaptic plasticity such as long-term potentiation. Further, IGF-1 enhances adult hippocampal neurogenesis though effects on proliferation and neuronal differentiation of neural progenitor cells and on dendritic growth of newly born neurons. Post-injury administration of IGF-1 has been effective in rodent models of TBI in improving learning and memory, attenuating death of mature hippocampal neurons and promoting neurogenesis, providing critical proof-of-concept data. More studies are needed to explore the effects of IGF-1-based therapies on synaptogenesis and synaptic plasticity following TBI and to optimize strategies in order to stimulate only appropriate, functional neuroplasticity.

Time Course of Homeostatic Structural Plasticity in Response to Optogenetic Stimulation in Mouse Anterior Cingulate Cortex

Plasticity is the mechanistic basis of development, aging, learning, and memory, both in healthy and pathological brains. Structural plasticity is rarely accounted for in computational network models due to a lack of insight into the underlying neuronal mechanisms and processes. Little is known about how the rewiring of networks is dynamically regulated. To inform such models, we characterized the time course of neural activity, the expression of synaptic proteins, and neural morphology employing an in vivo optogenetic mouse model. We stimulated pyramidal neurons in the anterior cingulate cortex of mice and harvested their brains at 1.5 h, 24 h, and $48\,\mathrm{h}$ after stimulation. Stimulus-induced cortical hyperactivity persisted up to 1.5 h and decayed to baseline after $24\,\mathrm{h}$ indicated by c-Fos expression. The synaptic proteins VGLUT1 and PSD-95, in contrast, were upregulated at $24\,\mathrm{h}$ and downregulated at $48\,\mathrm{h}$, respectively. Spine density and spine head volume were also increased at $24\,\mathrm{h}$ and decreased at $48\,\mathrm{h}$. This specific sequence of events reflects a continuous joint evolution of activity and connectivity that is characteristic of the model of homeostatic structural plasticity. Our computer simulations thus corroborate the observed empirical evidence from our animal experiments.

Postoperative cognitive dysfunction is made persistent with morphine treatment in aged rats

Postoperative cognitive dysfunction (POCD) is the collection of cognitive impairments, lasting days to months, experienced by individuals following surgery. Persistent POCD is most commonly experienced by older individuals and is associated with a greater vulnerability to developing Alzheimer's disease, but the underlying mechanisms are not known. It is known that laparotomy (exploratory abdominal surgery) in aged rats produces memory impairments for 4 days. Here we report that postsurgical treatment with morphine extends this deficit to at least 2 months while having no effects in the absence of surgery. Indeed, hippocampal-dependent long-term memory was impaired 2, 4, and 8 weeks postsurgery only in aged, morphine-treated rats. Short-term memory remained intact. Morphine is known to have analgesic effects via μ-opioid receptor activation and neuroinflammatory effects through Toll-like receptor 4 activation. Here we demonstrate that persistent memory deficits were mediated independently of the μ-opioid receptor, suggesting that they were evoked through a neuroinflammatory mechanism and unrelated to pain modulation. In support of this, aged, laparotomized, and morphine-treated rats exhibited increased gene expression of various proinflammatory markers (IL-1β, IL-6, TNFα, NLRP3, HMGB1, TLR2, and TLR4) in the hippocampus at the 2-week time point. Furthermore, central blockade of IL-1β signaling with the specific IL-1 receptor antagonist (IL-1RA), at the time of surgery, completely prevented the memory impairment. Finally, synaptophysin and PSD95 gene expression were significantly dysregulated in the hippocampus of aged, laparotomized, morphine-treated rats, suggesting that impaired synaptic structure and/or function may play a key role in this persistent deficit. This instance of long-term memory impairment following surgery closely mirrors the timeline of persistent POCD in humans and may be useful for future treatment discoveries.

Neurogranin: A Potential Biomarker of Neurological and Mental Diseases

Neurogranin (Ng) is a small protein usually expressed in granule-like structures in pyramidal cells of the hippocampus and cortex. However, its clinical value is not fully clear so far. Currently, Ng is proved to be involved in synaptic plasticity, synaptic regeneration, and long-term potentiation mediated by the calcium- and calmodulin-signaling pathways. Due to both the synaptic integrity and function as the growing concerns in the pathogenesis of a wide variety of neurological and mental diseases, a series of researches published focused on the associations between Ng and these kinds of diseases in the past decade. Therefore, in this review, we highlight several diseases, which include, but are not limited to, Alzheimer’s disease, Parkinson disease, Creutzfeldt–Jakob disease, neuro-HIV, neurosyphilis, schizophrenia, depression, traumatic brain injury, and acute ischemic stroke, and summarize the associations between cerebrospinal fluid or blood-derived Ng with these diseases. We propose that Ng is a potential and promising biomarker to improve the diagnosis, prognosis, and severity evaluation of these diseases in the future.