[Gly14]-Humanin reduces histopathology and improves functional outcome after traumatic brain injury in mice

Humanin derivative, HNG, enhances neurotransmitter release

BACKGROUND

Humanin (HN) is an endogenous 24-residue peptide that was first identified as a protective factor against neuronal death in Alzheimer's disease (AD). We previously demonstrated that the highly potent HN derivative HNG (HN with substitution of Gly for Ser14) ameliorated cognitive impairment in AD mouse models. Despite the accumulating evidence on the antagonizing effects of HN against cognitive deficits, the mechanisms behind these effects remain to be elucidated.

METHODS

The extracellular fluid in the hippocampus of wild-type young mice was collected by microdialysis and the amounts of neurotransmitters were measured. The kinetic analysis of exocytosis was performed by amperometry using neuroendocrine cells.

RESULTS

The hippocampal acetylcholine (ACh) levels were increased by intraperitoneal injection of HNG. HNG did not affect the physical activities of the mice but modestly improved their object memory. In a neuronal cell model, rat pheochromocytoma PC12 cells, HNG enhanced ACh-induced dopamine release. HNG increased ACh-induced secretory events and vesicular quantal size in primary neuroendocrine cells.

CONCLUSIONS

These findings suggest that HN directly enhances regulated exocytosis in neurons, which can contribute to the improvement of cognitive functions.

GENERAL SIGNIFICANCE

The regulator of exocytosis is a novel physiological role of HN, which provides a molecular clue for HN's effects on brain functions under health and disease.

Interleukin-13 Affects the Recovery Processes in a Mouse Model of Hemorrhagic Stroke with Bilateral Tibial Fracture

As one form of stroke, intracerebral hemorrhage (ICH) is a fatal cerebrovascular disease, which has high morbidity and mortality and lacks effective medical treatment. Increased infiltration of inflammatory cytokines coupled with pyroptotic cell death is involved in the pathophysiological process of ICH. However, little is known about whether concomitant fracture patients have the same progression of inflammation and pyroptosis. Hence, we respectively established the mouse ICH model and ICH with bilateral tibial fracture model (MI) to explore the potential cross-talk between the above two injuries. We found that MI obviously reversed the expressions of pyroptosis-associated proteins, which were remarkably up-regulated at the acute phase after ICH. Similar results were observed in neuronal expressions via double immunostaining. Furthermore, brain edema was also significantly alleviated in mice who suffered MI, when compared with ICH alone. To better clarify the potential mechanisms that mediated this cross-talk, recombinant mouse interleukin-13 (IL-13) was used to investigate its effect on pyroptosis in the mouse MI model, in which a lower level of IL-13 was observed. Remarkably, IL-13 administration re-awakened cell death, which was mirrored by the re-upregulation of pyroptosis-associated proteins and PI-positive cell counts. The results of hemorrhage volume and behavioral tests further confirmed its critical role in regulating neurological functions. Besides, the IL-13-treated MI group showed poor outcomes of fracture healing. To sum up, our research indicates that controlling the IL-13 content in the acute phase would be a promising target in influencing the outcomes of brain injury and fracture, and meanwhile, provides new evidence in repairing compound injuries in clinics.

Naringenin attenuates endoplasmic reticulum stress, reduces apoptosis, and improves functional recovery in experimental traumatic brain injury

Traumatic brain injury (TBI) is a significant cause of disability and death worldwide. Accumulating evidence suggests that endoplasmic reticulum (ER) stress would be an important component in the pathogenesis of TBI. Although the neuroprotective effects of naringenin, a natural flavonoid isolated from citrus plants, have been confirmed in several neurological diseases, its mechanism of action in TBI needs further investigation. In ICR mice, we found that TBI induced elevated expression of ER stress marker proteins, including 78-kDa glucose-regulated protein (GRP78) and C/EBP homologous protein (CHOP) in the perilesional cortex, which peaked at 7 days and 3 days after TBI, respectively. The induction of ER stress-related proteins partly coincided with ER architectural changes at 3 days post-TBI, indicating ER stress activation in our TBI model. Our results also revealed that continuous naringenin administration ameliorated neurological dysfunction, cerebral edema, plasmalemma permeability, and neuron cell loss at day 3 after TBI. Further, Naringenin suppressed TBI-induced activation of the ER stress pathway (p-eIF2α, ATF4, and CHOP), oxidative stress and apoptosis on day 3 after TBI. In summary, our data suggest that naringenin could ameliorate TBI-induced secondary brain injury by pleiotropic effects, including ER stress attenuation.

Chronic restraint stress exacerbates neurological deficits and disrupts the remodeling of the neurovascular unit in a mouse intracerebral hemorrhage model

Growing evidences have shown that patients recovering from stroke experience high and unremitting stress. Chronic restraint stress (CRS) has been found to exacerbate neurological impairments in an experimental focal cortical ischemia model. However, there have been no studies reporting the effect and mechanism of CRS on intracerebral hemorrhage (ICH). This study aimed to evaluate the effect of CRS on a mouse ICH model. Adult male C57BL mice were subjected to infusion of collagenase IV (to induce ICH) or saline (for sham) into the left striatum. After ICH, animals were stressed with application of CRS protocol for 21 days. Our results showed that CRS significantly exacerbated neurological deficits (Garcia test, corner turn test, and wire grip test) and the ipsilateral brain atrophy and reduced body weight gain after ICH. Immunofluorescence staining indicated that CRS exerted significant suppressive effects on neuron, astrocyte, vascular endothelial cell and pericyte and excessively activated microglia post ICH. All of the key cellular components mentioned above are involved in the neurovascular unit (NVU) remodeling in the peri-hemorrhagic region after ICH. Western blot results showed that matrix metalloproteinase (MMP)-9 and tight junction (TJ) proteins including zonula occludens-1, occludin and claudin-5 were increased after ICH, but MMP-9 protein was further up-regulated and TJ-related proteins were down-regulated by CRS. In addition, ICH-induced activation of endoplasmic reticulum stress and apoptosis were further strengthened by CRS. Collectively, CRS exacerbates neurological deficits and disrupts the remodeling of the peri-hemorrhagic NVU after ICH, which may be associated with TJ proteins degradation and excessive activation of MMP-9 and endoplasmic reticulum stress-apoptosis.LAY SUMMARYCRS exacerbates neurological deficits and disrupts the remodeling of the NVU in the recovery stage after ICH, which suggest that monitoring chronic stress levels in patients recovering from ICH may merit consideration in the future.

The Function and Mechanisms of Autophagy in Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the most common causes of long-term disability and death worldwide. Autophagy is activated and autophagic flux is impaired following TBI. But the controversial roles and underlying mechanisms of autophagy after TBI are not clear. This chapter will update the current state of knowledge in the process of autophagy, the roles of autophagy in TBI as well as some upstream moleculars and pharmacological regulators of autophagy involved in TBI. We also discuss autophagy mechanism-based preclinical pharmacological intervention. These observations make autophagy an attractive therapeutic target for developing new therapeutic strategies to achieve better outcomes for patients suffering from TBI.

Modulation of autophagy in traumatic brain injury

Traumatic brain injury (TBI) is defined as a traumatically induced structural injury or physiological disruption of brain function as a result of external forces, leading to adult disability and death. A growing body of evidence reveals that alterations in autophagy-related proteins exist extensively in both experimentally and clinically after TBI. Of note, the autophagy pathway plays an essential role in pathophysiological processes, such as oxidative stress, inflammatory response, and apoptosis, thus contributing to neurological properties of TBI. With this in mind, this review summarizes a comprehensive overview on the beneficial and detrimental effects of autophagy in pathophysiological conditions and how these activities are linked to the pathogenesis of TBI. Moreover, the relationship between oxidative stress, inflammation, apoptosis, and autophagy occur TBI. Ultimately, multiple compounds and various drugs targeting the autophagy pathway are well described in TBI. Therefore, autophagy flux represents a potential clinical therapeutic value for the treatment of TBI and its complications.

Salubrinal offers neuroprotection through suppressing endoplasmic reticulum stress, autophagy and apoptosis in a mouse traumatic brain injury model

Traumatic brain injury (TBI) is a complex injury that can cause severe disabilities and even death. TBI can induce secondary injury cascades, including but not limited to endoplasmic reticulum (ER) stress, apoptosis and autophagy. Although the investigators has previously shown that salubrinal, the selective phosphatase inhibitor of p-eIF2α, ameliorated neurologic deficits in murine TBI model, the neuroprotective mechanisms of salubrinal need further research to warrant the preclinical value. This study was undertaken to characterize the effects of salubrinal on cell death and neurological outcomes following TBI in mice and the potential mechanisms. In the current study, ER stress-related proteins including p-eIF2α, GRP78 and CHOP showed peak expressions both in the cortex and hippocampus from day 2 to day 3 after TBI, indicating ER stress was activated in our TBI model. Immunofluorescence staining showed that CHOP co-located NeuN-positive neuron, GFAP-positive astrocyte, Iba-1-positive microglia, CD31-positive vascular endothelial cell and PDGFR-β-positive pericyte in the cortex on day 2 after TBI, and these cells mentioned above constitute the neurovascular unit (NVU). We also found TBI-induced plasmalemma permeability, motor dysfunction, spatial learning and memory deficits and brain lesion volume were alleviated by continuous intraperitoneal administration of salubrinal post TBI. To investigate the underlying mechanisms further, we determined that salubrinal suppressed the expression of ER stress, autophagy and apoptosis related proteins on day 2 after TBI. In addition, salubrinal administration decreased the number of CHOP+/TUNEL+ and CHOP+/LC3+ cells on day 2 after TBI, detected by immunofluorescence. In conclusion, these data imply that salubrinal treatment improves morphological and functional outcomes caused by TBI in mice and these neuroprotective effects may be associated with inhibiting apoptosis, at least in part by suppressing ER stress-autophagy pathway.

Inhibition of autophagy after perforator flap surgery increases flap survival and angiogenesis

BACKGROUND

The survival ratio of multiterritory perforator flap is variable. Therefore, surviving mechanisms are increasingly explored to identify novel therapeutics. The condition of the choke zone is essential for perforator flap survival. In this study, we investigated autophagy in the choke zone after flap surgery.

MATERIALS AND METHODS

The flap model involved a perforator flap with three territories that was located on the right dorsal side of a rat. A total of 36 rats were divided into six groups, including the control, 0 d postoperative (PO), 1, 3, 5, and 7 d PO groups. In addition, 72 rats were divided into three groups, including a control group, a 3-methyladenine (3-MA) group, and a rapamycin group. Skin tissue of rats was used for measuring autophagy proteins, vascular endothelial growth factor (VEGF) expression, and histological examination. On day 7 after surgery, the survival ratio of each flap was determined.

RESULTS

The expression of autophagy and VEGF in the second choke zone (choke II) was increased after flap surgery. Among the three groups, the survival ratio of flaps in the 3-MA group was the highest. Furthermore, the angiogenesis level in the 3-MA group in choke II was the highest among the three groups.

CONCLUSIONS

Autophagy was initiated by surgery in choke II, and VEGF expression in choke II was increased after flap surgery. Inhibiting autophagy after perforator flap surgery is beneficial for flap survival and for promoting angiogenesis in choke II.

Autophagy in Traumatic Brain Injury: A New Target for Therapeutic Intervention

Traumatic brain injury (TBI) is one of the most devastating forms of brain injury. Many pathological mechanisms such as oxidative stress, apoptosis and inflammation all contribute to the secondary brain damage and poor outcomes of TBI. Current therapies are often ineffective and poorly tolerated, which drive the explore of new therapeutic targets for TBI. Autophagy is a highly conserved intracellular mechanism during evolution. It plays an important role in elimination abnormal intracellular proteins or organelles to maintain cell stability. Besides, autophagy has been researched in various models including TBI. Previous studies have deciphered that regulation of autophagy by different molecules and pathways could exhibit anti-oxidative stress, anti-apoptosis and anti-inflammation effects in TBI. Hence, autophagy is a promising target for further therapeutic development in TBI. The present review provides an overview of current knowledge about the mechanism of autophagy, the frequently used methods to monitor autophagy, the functions of autophagy in TBI as well as its potential molecular mechanisms based on the pharmacological regulation of autophagy.

Glucocorticoid treatment inhibits intracerebral hemorrhage‑induced inflammation by targeting the microRNA‑155/SOCS‑1 signaling pathway

Intracerebral hemorrhage (ICH) results in inflammation, and glucocorticoids have been proven to be effective inhibitors of ICH‑induced inflammation. However, the precise underlying mechanisms of ICH‑induced inflammation and glucocorticoid function remain largely undefined. Using a mouse ICH model, the present study demonstrated that the short non‑coding RNA molecule microRNA‑155 (miR‑155) is involved in the inflammatory process initiated by ICH in mice. Increased mRNA expression levels of miR‑155, as well as the pro‑inflammatory cytokines interferon‑β (IFN‑β), tumor necrosis factor‑α (TNF‑α) and interleukin‑6 (IL‑6), were observed in vivo following ICH. By contrast, the expression level of suppressor of cytokine signaling 1 (SOCS‑1) protein was reduced in the ICH group compared with control mice. Similar results were observed in vitro using astrocytes, the primary effector cells in ICH. Compared with wild type astrocytes, astrocytes overexpressing miR‑155 exhibited significant inhibition of SOCS‑1 protein expression levels. These results suggest that miR‑155 contributes to the development of ICH‑induced inflammation in mice by downregulating SOCS‑1 protein expression levels and promoting pro‑inflammatory cytokine (IFN‑β, TNF‑α and IL‑6) production. Expression levels of miR‑155 and pro‑inflammatory cytokines in the ICH group were significantly decreased following dexamethasone administration. This suggests that glucocorticoids attenuate ICH‑induced inflammation by targeting the miR‑155/SOCS‑1 signaling pathway in mice. In conclusion, the results of the present study demonstrated that the miR‑155/SOCS‑1 signaling pathway is required for ICH‑induced inflammation, and glucocorticoids inhibit this process by targeting the miR‑155/SOCS‑1 signaling pathway.

Mechanisms of cell-cell interaction in oligodendrogenesis and remyelination after stroke

White matter damage is a clinically important aspect of several central nervous system diseases, including stroke. Cerebral white matter primarily consists of axonal bundles ensheathed with myelin secreted by mature oligodendrocytes, which play an important role in neurotransmission between different areas of gray matter. During the acute phase of stroke, damage to oligodendrocytes leads to white matter dysfunction through the loss of myelin. On the contrary, during the chronic phase, white matter components promote an environment, which is favorable for neural repair, vascular remodeling, and remyelination. For effective remyelination to take place, oligodendrocyte precursor cells (OPCs) play critical roles by proliferating and differentiating into mature oligodendrocytes, which help to decrease the burden of axonal injury. Notably, other types of cells contribute to these OPC responses under the ischemic conditions. This mini-review summarizes the non-cell autonomous mechanisms in oligodendrogenesis and remyelination after white matter damage, focusing on how OPCs receive support from their neighboring cells. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Protective effects of Humanin and calmodulin-like skin protein in Alzheimer's disease and broad range of abnormalities

Humanin is a 24-amino acid, secreted bioactive peptide that prevents various types of cell death and improves some types of cell dysfunction. Humanin inhibits neuronal cell death that is caused by a familial Alzheimer's disease (AD)-linked gene via binding to the heterotrimeric Humanin receptor (htHNR). This suggests that Humanin may play a protective role in AD-related pathogenesis. Calmodulin-like skin protein (CLSP) has recently been identified as a physiological agonist of htHNR with 10(5)-fold more potent anti-cell death activity than Humanin. Humanin has also shown to have protective effects against some metabolic disorders. In this review, the broad range of functions of Humanin and the functions of CLSP that have been characterized thus far are summarized.

The effects of BMSCs transplantation on autophagy by CX43 in the hippocampus following traumatic brain injury in rats

Traumatic brain injury (TBI) can initiate a series of complicated pathological events, and induce various types of neuronal cell death including autophagy and apoptosis. Currently, the treatment of TBI is one of the main challenges in neurobiology. In this regard, the administration of bone marrow stromal cells (BMSCs) represents a novel treatment modality for TBI. However, the protective mechanism of BMSCs was unknown in the TBI. The aim of the present study was to assess the effects of BMSCs on connexin 43(CX43) and autophagy in the hippocampus following TBI in rats. A rat model of TBI was created using a modified weight-drop device. Double-membrane structures in the process of autophagy formation were frequently observed in injured brain by electron microscopy. The levels of autophagic pathway associated proteins and CX43 were also detected by western blot analysis. Specifically, immunoblotting results showed that BMSCs treatment after TBI could down-regulate light chain 3 (LC3), Beclin-1 and CX43 expression in the hippocampus. Taken together, our results demonstrated that BMSCs were able to significantly suppress TBI-induced autophagy activity, and the potential mechanism by regulating CX43 levels.