The role of peripheral benzodiazepine receptors on the function and survival of isolated human pancreatic islets

TSPO in pancreatic beta cells and its possible involvement in type 2 diabetes

Amyloidosis forms a large family of pathologies associated with amyloid deposit generated by the formation of amyloid fibrils or plaques. The amyloidogenic proteins and peptides involved in these processes are targeted against almost all organs. In brain they are associated with neurodegenerative disease, and the Translocator Protein (TSPO), overexpressed in these inflammatory conditions, is one of the target for the diagnostic. Moreover, TSPO ligands have been described as promising therapeutic drugs for neurodegenerative diseases. Type 2 diabetes, another amyloidosis, is due to a beta cell mass decrease that has been linked to hIAPP (human islet amyloid polypeptide) fibril formation, leading to the reduction of insulin production. In the present study, in a first approach, we link overexpression of TSPO and inflammation in potentially prediabetic patients. In a second approach, we observed that TSPO deficient rats have higher level of insulin secretion in basal conditions and more IAPP fibrils formation compared with wild type animals. In a third approach, we show that diabetogenic conditions also increase TSPO overexpression and IAPP fibril formation in rat beta pancreatic cell line (INS-1E). These data open the way for further studies in the field of type 2 diabetes treatment or prevention.

Midazolam suppresses ischemia/reperfusion-induced cardiomyocyte apoptosis by inhibiting the JNK/p38 MAPK signaling pathway

Myocardial ischemia/reperfusion (I/R) injury causes irreversible injury to the heart, thereby causing acute myocardial infarction. Midazolam is a benzodiazepine commonly utilized in anesthesia and intensive care. Research has indicated that midazolam plays a critical role in many diseases; however, the function of midazolam in myocardial injury induced by I/R still needs further investigation. The infarct size and damage to the heart tissues were examined through 2,3,5-triphenyl tetrazolium chloride (TTC) staining and hematoxylin and eosin staining. The creatine kinase-myocardial band isoenzyme, lactate dehydrogenase, and aspartate aminotransferase levels were tested using commercial kits. Cell apoptosis was determined through TUNEL staining or flow cytometry assays. Bax, Bcl-2, cleaved caspase-3, phospho-38 (p-p38), p38, p-JNK, JNK, extracellular signal-regulated kinases (ERK), and p-ERK expression was examined through Western blot. In our study, midazolam was shown to suppress the infarct size and heart tissue damage and reduce myocardial enzyme leakage in I/R rats. Additionally, midazolam was found to retard cardiomyocyte apoptosis in I/R rats. The JNK/p38 MAPK signaling pathway in I/R rats was inhibited by midazolam. Our findings demonstrated that in hypoxia/reoxygenation (H/R) - mediated H9C2 cells, anisomycin abolished the suppressive effects of midazolam on the JNK/p38 MAPK signaling pathway. Next, exploration discovered that anisomycin abolished the cytoprotective effects of midazolam on H/R-treated H9C2 cell apoptosis. In conclusion, this work demonstrated that midazolam retarded I/R-induced cardiomyocyte apoptosis by inhibiting the JNK/p38 MAPK signaling pathway. These results may provide new insight into the treatment of myocardial I/R injury.

The Potential Role of Pancreatic γ-Aminobutyric Acid (GABA) in Diabetes Mellitus: A Critical Reappraisal

Background

Diabetes mellitus (DM) is an endocrine disorder characterized by hyperglycemia, polyuria, polydipsia, and glucosuria. γ-aminobutyric acid (GABA) is an inhibitory neurotransmitter in the central nervous system (CNS) of humans and other mammals. GABA acts on two different receptors, which are GABA-_A and GABA-_B. Pancreatic β-cells synthesize GABA from glutamic acid by glutamic acid decarboxylase (GAD).

Aim

The objective of this study was to explore the potential role of pancreatic GABA on glycemic indices in DM.

Methods

Evidence from experimental, preclinical, and clinical studies are evaluated for bidirectional relationships between pancreatic GABA and blood glucose disorders. A multiplicity of search strategies took on and assumed included electronic database searches of Medline and Pubmed using MeSH terms, keywords and title words during the search.

Results

The pancreatic GABA signaling system has a role in the regulation of pancreatic hormone secretions, inhibition of immune response, improve β-cells survival, and change α cell into β-cell. Moreover, a GABA agonist improves the antidiabetic effects of metformin. In addition, benzodiazepine receptor agonists improve pancreatic β-cell functions through GABA dependent pathway or through modulation of pancreatic adenosine and glucagon-like peptide (GLP-1).

Conclusions

Pancreatic GABA improves islet cell function, glucose homeostasis, and autoimmunity in DM. Orally administered GABA is safe for humans, and acts on peripheral GABA receptors and represents a new therapeutic modality for both T1DM and T2DM. Besides, GABA-_A receptor agonist like benzodiazepines improves pancreatic β-cell function and insulin sensitivity through activation of GABA-_A receptors.

Development and validation of a quantitative electron microscopy score to assess acute cellular stress in the human exocrine pancreas

The pancreas is particularly sensitive to acute cellular stress, but this has been difficult to evaluate using light microscopy. Pancreatic ischaemia associated with deceased organ donation negatively impacts whole‐organ and isolated‐islet transplantation outcomes. Post‐mortem changes have also hampered accurate interpretation of ante‐mortem pancreatic pathology. A rigorous histological scoring system accurately quantifying ischaemia is required to experimentally evaluate innovations in organ preservation and to increase rigour in clinical/research evaluation of underlying pancreatic pathology. We developed and validated an unbiased electron microscopy (EM) score of acute pancreatic exocrine cellular stress in deceased organ donor cohorts (development [n = 28] and validation [n = 16]). Standardised assessment led to clearly described numerical scores (0–3) for nuclear, mitochondrial and endoplasmic reticulum (ER) morphology and intracellular vacuolisation; with a maximum (worst) aggregate total score of 12. In the Validation cohort, a trend towards higher scores was observed for tail versus head regions (nucleus score following donation after brainstem death [DBD]: head 0.67 ± 0.19; tail 0.86 ± 0.11; p = 0.027) and donation after circulatory death (DCD) versus DBD (mitochondrial score: DCD (head + tail) 2.59 ± 0.16; DBD (head + tail) 2.38 ± 0.21; p = 0.004). Significant mitochondrial changes were seen ubiquitously even with short cold ischaemia, whereas nuclear and vacuolisation changes remained mild even after prolonged ischaemia. ER score correlated with cold ischaemia time (CIT) following DBD (pancreatic tail region: r = 0.796; p = 0.018). No relationships between CIT and EM scores were observed following DCD. In conclusion, we have developed and validated a novel EM score providing standardised quantitative assessment of subcellular ultrastructural morphology in pancreatic acinar cells. This provides a robust novel tool for gold standard measurement of acute cellular stress in studies evaluating surrogate measures of peri‐transplant ischaemia, organ preservation technologies and in samples obtained for detailed pathological examination of underlying pancreatic pathology.

Respective effects of oxygen and energy substrate deprivation on beta cell viability

Deficit in oxygen and energetic substrates delivery is a key factor in islet loss during islet transplantation. Permeability transition pore (PTP) is a mitochondrial channel involved in cell death. We have studied the respective effects of oxygen and energy substrate deprivation on beta cell viability as well as the involvement of oxidative stress and PTP opening. Energy substrate deprivation for 1h followed by incubation in normal conditions led to a cyclosporin A (CsA)-sensitive-PTP-opening in INS-1 cells and human islets. Such a procedure dramatically decreased INS-1 cells viability except when transient removal of energy substrates was performed in anoxia, in the presence of antioxidant N-acetylcysteine (NAC) or when CsA or metformin inhibited PTP opening. Superoxide production increased during removal of energy substrates and increased again when normal energy substrates were restored. NAC, anoxia or metformin prevented the two phases of oxidative stress while CsA prevented the second one only. Hypoxia or anoxia alone did not induce oxidative stress, PTP opening or cell death. In conclusion, energy substrate deprivation leads to an oxidative stress followed by PTP opening, triggering beta cell death. Pharmacological prevention of PTP opening during islet transplantation may be a suitable option to improve islet survival and graft success.

Diazepam potentiates the antidiabetic, antistress and anxiolytic activities of metformin in type-2 diabetes mellitus with cooccurring stress in experimental animals

Psychological stress is considered as one of the limiting factors in the management of type-2 diabetes mellitus (T2DM). Therefore, the basic objective of the present study was to evaluate the antidiabetic effect of metformin, diazepam, and their combination in cooccurring T2DM and stress condition (DMS). T2DM was induced in the male rats by administering streptozotocin (45 mg/kg, i.p.) and nicotinamide (110 mg/kg, i.p.) with time lag of 15 min. Rats were subjected to two sessions of cold restraint stress paradigm for one hour on the sixth and seventh day after streptozotocin injection. Administration of metformin (25 mg/kg, p.o.) and diazepam (1 mg/kg, p.o.) in combination from the seventh to thirteenth day after streptozotocin injection showed better improvement in glucose tolerance and insulin sensitivity compared to monotherapy of either drug. In addition, the combination significantly attenuated DMS-induced hyperglycemia, hypertriglyceridaemia, hypercorticosteronemia, anxiety-like behavior, and insulin resistance through modulating insulin signaling pathway in the liver compared to monotherapy. Further, improvement of mitochondrial function, integrity, and oxidative stress in hippocampus, hypothalamus, prefrontal cortex, striatum, amygdala, and nucleus accumbens was observed with the combination. Therefore, metformin in combination with diazepam may be a better therapeutic option in the management of T2DM with cooccurring stress condition.

The 18 kDa translocator protein influences angiogenesis, as well as aggressiveness, adhesion, migration, and proliferation of glioblastoma cells

BACKGROUND

It is known that the mitochondrial 18 kDa translocator protein (TSPO) is present in almost all peripheral tissues and also in glial cells in the brain. TSPO levels are typically enhanced in correlation with tumorigenesis of cancer cells including glioblastoma. Relevant for angiogenesis, TSPO is also present in almost all cells of the cardiovascular system.

METHODS

We studied the effect of TSPO knockdown by siRNA on various aspects of tumor growth of U118MG glioblastoma cells in two in-vivo models: a nude mouse model with intracerebral implants of U118MG glioblastoma cells and implantation of U118MG glioblastoma cells on the chorionallantoic membrane (CAM) of chicken embryos. In vitro, we further assayed the influence of TSPO on the invasive potential of U118MG cells.

RESULTS

TSPO knockdown increased tumor growth in both in-vivo models compared with the scrambled siRNA control. Angiogenesis was also increased by TSPO knockdown as determined by a CAM assay. TSPO knockdown led to a decrease in adhesion to the proteins of the extracellular matrix, including fibronectin, collagen I, collagen IV, laminin I, and fibrinogen. TSPO knockdown also led to an enhancement in the migratory capability of U118MG cells, as determined in a modified Boyden chamber. Application of the TSPO ligand 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195) at a concentration of 25 µmol/l in the in-vitro models yielded results similar to those obtained on TSPO knockdown. We found no effects of PK 11195 on TSPO protein expression. Interestingly, at low nmol/l concentrations (around 1 nmol/l), PK 11195 enhanced adhesion to collagen I, suggesting a bimodal concentration effect of PK 11195.

CONCLUSION

Intact TSPO appears to be able to counteract the invasive and angiogenic characteristics related to the aggressiveness of U118MG glioblastoma cells in vivo and in vitro.

PK11195, a specific ligand of the peripheral benzodiazepine receptor, may protect pancreatic beta-cells from cytokine-induced cell death

We cultured isolated islets from human or porcine origin in the presence or absence of IL1 and TNFα and studied cytoprotective effects of two structurally different PBR ligands. Storage of pig or human islets in the presence of cytokines significantly lowered the fraction of vital beta-cells. Compared with cytokine incubations PK11195 alone or in combination with cytokines was effective to prevent cytokine induced cell death. The data indicate that cold storage in the presence of PK11195 may further protect beta-cells from cytokine induced cell death. This ligand may be helpful to preserve beta-cell survival before transplantation.

Protection of pancreatic INS-1 β-cells from glucose- and fructose-induced cell death by inhibiting mitochondrial permeability transition with cyclosporin A or metformin

Hyperglycemia is detrimental to β-cell viability, playing a major role in the progression of β-cell loss in diabetes mellitus. The permeability transition pore (PTP) is a mitochondrial channel involved in cell death. Recent evidence suggests that PTP inhibitors prevent hyperglycemia-induced cell death in human endothelial cells. In this work, we have examined the involvement of PTP opening in INS-1 cell death induced by high levels of glucose or fructose. PTP regulation was studied by measuring the calcium retention capacity in permeabilized INS-1 cells and by confocal microscopy in intact INS-1 cells. Cell death was analyzed by flow cytometry. We first reported that metformin and cyclosporin A (CsA) prevented Ca²⁺-induced PTP opening in permeabilized and intact INS-1 cells. We then showed that incubation of INS-1 cells in the presence of 30 mM glucose or 2.5 mM fructose induced PTP opening and led to cell death. As both metformin and CsA prevented glucose- and fructose- induced PTP opening, and hampered glucose- and fructose- induced cell death, we conclude that PTP opening is involved in high glucose- and high fructose- induced INS-1 cell death. We therefore suggest that preventing PTP opening might be a new approach to preserve β-cell viability.

Effect of progesterone on phosphamidon-induced impairment of memory and oxidative stress in rats

Progesterone (a neurosteroid) is an important modulator of the nervous system functioning. Organophosphorus pesticides like phosphamidon have been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was therefore designed to investigate the effects of progesterone (PROG) on phosphamidon-induced modulation of cognitive function and oxidative stress in rats. Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on an elevated plus maze. Oxidative stress was assessed by examining the levels of thiobarbituric acid reactive species (TBARS) and non-protein thiols (NP-SH) in isolated homogenized whole brain samples. The results showed a significant reduction in SDL and prolongation of TL in the phosphamidon (1.74 mg/kg/d; p.o.) treated group at weeks 6 and 8 as compared to the control group. Two weeks treatment with PROG (15 mg/kg/d; i.p.) antagonized the effect of phosphamidon on SDL as well as TL. Phosphamidon alone produced a significant increase in the brain TBARS levels and decrease in the brain NP-SH levels. Treatment with PROG (15 mg/kg/d; i.p.) attenuated the effect of phosphamidon on oxidative stress. Together, the results showed that progesterone attenuated the cognitive dysfunction and increased oxidative stress induced by phosphamidon in the brain.

Reversal of propoxur-induced impairment of memory and oxidative stress by 4'-chlorodiazepam in rats

Carbamate pesticides like propoxur have been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of the effects of propoxur over cognitive function by progesterone (PROG) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus, transfer latency (TL) on a plus maze and spatial navigation test on Morris water maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and reduced glutathione (GSH) levels and catalase (CAT) activity. A significant reduction in SDL and prolongation of TL and spatial navigation test was found for the propoxur (10 mg/kg/d; p.o.) treated group at weeks 6 and 7 as compared with control. One-week treatment with 4CD (0.5 mg/kg/d; i.p.) antagonized the effect of propoxur on SDL, spatial navigation test as well as TL; whereas, PROG failed to modulate this effect at a dose of 15 mg/kg/d, i.p. Propoxur produced a statistically significant increase in the brain MDA levels and decrease in the brain GSH levels and CAT activity. Treatment with 4CD at the above dose attenuated the effect of propoxur on oxidative stress whereas PROG (15 mg/kg/d; i.p.) failed to influence the same. The results of the present study thus show that 4-CD has the potential to attenuate cognitive dysfunction and oxidative stress induced by toxicants like propoxur in the brain.

Deletion of PKCepsilon selectively enhances the amplifying pathways of glucose-stimulated insulin secretion via increased lipolysis in mouse beta-cells

OBJECTIVE

Insufficient insulin secretion is a hallmark of type 2 diabetes, and exposure of beta-cells to elevated lipid levels (lipotoxicity) contributes to secretory dysfunction. Functional ablation of protein kinase C epsilon (PKCepsilon) has been shown to improve glucose homeostasis in models of type 2 diabetes and, in particular, to enhance glucose-stimulated insulin secretion (GSIS) after lipid exposure. Therefore, we investigated the lipid-dependent mechanisms responsible for the enhanced GSIS after inactivation of PKCepsilon.

RESEARCH DESIGN AND METHODS

We cultured islets isolated from PKCepsilon knockout (PKCepsilonKO) mice in palmitate prior to measuring GSIS, Ca(2+) responses, palmitate esterification products, lipolysis, lipase activity, and gene expression.

RESULTS

The enhanced GSIS could not be explained by increased expression of another PKC isoform or by alterations in glucose-stimulated Ca(2+) influx. Instead, an upregulation of the amplifying pathways of GSIS in lipid-cultured PKCepsilonKO beta-cells was revealed under conditions in which functional ATP-sensitive K(+) channels were bypassed. Furthermore, we showed increased esterification of palmitate into triglyceride pools and an enhanced rate of lipolysis and triglyceride lipase activity in PKCepsilonKO islets. Acute treatment with the lipase inhibitor orlistat blocked the enhancement of GSIS in lipid-cultured PKCepsilonKO islets, suggesting that a lipolytic product mediates the enhancement of glucose-amplified insulin secretion after PKCepsilon deletion.

CONCLUSIONS

Our findings demonstrate a mechanistic link between lipolysis and the amplifying pathways of GSIS in murine beta-cells, and they suggest an interaction between PKCepsilon and lipolysis. These results further highlight the therapeutic potential of PKCepsilon inhibition to enhance GSIS from the beta-cell under conditions of lipid excess.

Ro5-4864 promotes neonatal motor neuron survival and nerve regeneration in adult rats

The translocator protein (18 kDa; TSPO), formerly known as the peripheral benzodiazepine receptor, is an outer mitochondrial membrane protein that associates with the mitochondrial permeability transition pore to regulate both steroidogenesis and apoptosis. TSPO expression is induced in adult dorsal root ganglion (DRG) sensory neurons after peripheral nerve injury and a TSPO receptor ligand, Ro5-4864, enhances DRG neurite growth in vitro and axonal regeneration in vivo. We have now found that TSPO is induced in neonatal motor neurons after peripheral nerve injury and have evaluated its involvement in neonatal and adult sensory and motor neuron survival, and in adult motor neuron regeneration. The TSPO ligand Ro5-4864 rescued cultured neonatal DRG neurons from nerve growth factor withdrawal-induced apoptosis and protected neonatal spinal cord motor neurons from death due to sciatic nerve axotomy. However, Ro5-4864 had only a small neuroprotective effect on adult facial motor neurons after axotomy, did not delay onset or prolong survival in SOD1 mutant mice, and failed to protect adult DRG neurons from sciatic nerve injury-induced death. In contrast, Ro5-4864 substantially enhanced adult facial motor neuron nerve regeneration and restoration of function after facial nerve axotomy. These data indicate a selective sensitivity of neonatal sensory and motor neurons to survival in response to Ro5-4864, which highlights that survival in injured immature neurons cannot necessarily predict success in adults. Furthermore, although Ro5-4864 is only a very weak promoter of survival in adult neurons, it significantly enhances regeneration and functional recovery in adults.

Translocator protein 18 kDa is involved in the regulation of reactive gliosis

Translocator protein (18 kDa) (TSPO), previously known as peripheral-type benzodiazepine receptor, is a critical component of the mitochondrial permeability transition pore. Brain inflammation results in the induction of the expression of TSPO in glial cells and some TSPO ligands decrease reactive gliosis after brain injury. However, since some TSPO ligands are neuroprotective, their effects on reactive gliosis may be the consequence of a reduced neurodegeneration. To assess whether TSPO ligands can modulate reactive gliosis in absence of neuronal death, we have tested their effects on the inflammatory response induced in the hippocampus of male rats by the intracerebroventricular infusion of lipopolysaccharide (LPS). LPS treatment did not induce neuronal death, assessed by Fluoro jade-B staining, but increased the number of cells immunoreactive for vimentin and MHC-II, used as markers of reactive astrocytes and reactive microglia, respectively. Furthermore, LPS produced an increase in the number of proliferating microglia. The TSPO ligand PK11195 reduced the number of MHC-II immunoreactive cells and the proliferation of microglia in LPS treated rats. In contrast, another TSPO ligand, Ro5-4864, did not significantly affect the response of microglia to LPS. Neither PK11195 nor Ro5-4864 affected the LPS-mediated increase in the number of vimentin-immunoreactive astrocytes at the time point studied, although PK11195 reduced vimentin immunoreactivity. These findings identify TSPO as a potential target for controlling neural inflammation, showing that the TSPO ligand PK11195 may reduce microglia activation by a mechanism that is independent of the regulation of neuronal survival.

Reversal of lindane-induced impairment of step-down passive avoidance and oxidative stress by neurosteroids in rats

Neurosteroids (NS) are recognized as important modulators of functioning of the nervous system. Lindane, an organochlorine pesticide has been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of effects of lindane over cognitive function by progesterone (PROG), pregnenolone sulfate (PREG-S) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on a plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL was found for the lindane treated group at weeks 6 and 7 as compared to control (p<0.001). One-week treatment by PREG-S or 4CD antagonized the effect of lindane on SDL. PROG failed to modulate the effect of lindane on SDL. Lindane caused a significant prolongation of TL as compared to control (p<0.001) from second week onwards. One-week administration of PROG, PREG-S or 4CD was unable to reverse this prolongation of TL. Lindane produced a statistically significant increase in the brain MDA levels (p<0.001) and significant decrease in the brain NP-SH levels (p<0.001). Treatment with PREG-S and 4CD attenuated the effect of lindane on MDA (p<0.001) and NP-SH levels. PROG failed to influence oxidative stress induced by lindane. Results of the present study thus show that some NS have potential in reversing cognitive dysfunction and oxidative stress induced by toxicants like lindane in the brain.

Decreased GABAA Receptor Function in the Brain Stem during Pancreatic Regeneration in Rats

Gamma amino butyric acid is a major inhibitory neurotransmitter in the central nervous system. In the present study we have investigated the alteration of GABA receptors in the brain stem of rats during pancreatic regeneration. Three groups of rats were used for the study: sham operated, 72 h and 7 days partially pancreatectomised. GABA was quantified by [(3)H]GABA receptor displacement method. GABA receptor kinetic parameters were studied by using the binding of [(3)H]GABA as ligand to the Triton X-100 treated membranes and displacement with unlabelled GABA. GABA(A) receptor activity was studied by using the [(3)H]bicuculline and displacement with unlabelled bicuculline. GABA content significantly decreased (P < 0.001) in the brain stem during the regeneration of pancreas. The high affinity GABA receptor binding showed a significant decrease in B(max) (P < 0.01) and K(d) (P < 0.05) in 72 h and 7 days after partial pancreatectomy. [(3)H]bicuculline binding showed a significant decrease in B(max) and K(d) (P < 0.001) in 72 h pancreatectomised rats when compared with sham where as B(max) and K(d) reversed to near sham after 7 days of pancreatectomy. The results suggest that GABA through GABA receptors in brain stem has a regulatory role during active regeneration of pancreas which will have immense clinical significance in the treatment of diabetes.

Steroidogenic acute regulatory protein in the brain

The nervous system synthesizes steroids that regulate the development and function of neurons and glia, and have neuroprotective properties. The first step in steroidogenesis involves the delivery of free cholesterol to the inner mitochondrial membrane where it can be converted into pregnenolone by the enzyme cytochrome P450side chain cleavage. The peripheral-type benzodiazepine receptor and the steroidogenic acute regulatory protein are involved in this process and appear to function in a coordinated manner. Steroidogenic acute regulatory protein mRNA and protein are widely expressed throughout the adult brain. Steroidogenic acute regulatory protein expression has been detected in many neuronal populations, in ependymocytes, in some astroglial cells, in Schwann cells from peripheral nerves and in proliferating cells of the developing and adult brain. Steroidogenic acute regulatory protein is colocalized in the same neural cells with P450side chain cleavage and with other steroidogenic enzymes. Steroidogenic acute regulatory protein expression in the brain shows marked changes with development, aging and injury. The steroidogenic acute regulatory protein gene may be under the control of diverse mechanisms in different neural cell types, since its expression is upregulated by cyclic AMP (cAMP) in gliomas and astrocytes in culture and downregulated by cyclic AMP (cAMP) in Schwann cells. In addition, activation of N-methyl-D-aspartate receptors, and the consequent rise in intracellular calcium levels, activates steroidogenic acute regulatory protein and steroidogenesis in hippocampal neurons. In conclusion, steroidogenic acute regulatory protein is regulated in the nervous system by different physiological and pathological conditions and may play an important role during brain development, aging and after injury.

Ro5-4864, a peripheral benzodiazepine receptor ligand, reduces reactive gliosis and protects hippocampal hilar neurons from kainic acid excitotoxicity

The peripheral-type benzodiazepine receptor (PBR) is a critical component of the mitochondrial permeability transition pore, which is involved in the regulation of cell survival. Different forms of brain injury result in induction of the expression of the PBR in the areas of neurodegeneration, mainly in reactive glial cells. The consequences of induction of PBR expression after brain injury are unknown. To test whether PBR may be involved in the regulation of neuronal survival after injury, we have assessed the effect of two PBR ligands, Ro5-4864 and PK11195, on neuronal loss induced by kainic acid in the hippocampus. Systemic administration of kainic acid to male rats resulted in the induction of a reactive phenotype in astrocytes and microglia and in a significant loss of hilar neurons in the dentate gyrus. Administration of Ro5-4864, before the injection of kainic acid, decreased reactive gliosis in the hilus and prevented hilar neuronal loss. In contrast, PK11195 was unable to reduce reactive gliosis and did not protect hilar neurons from kainic acid. These findings suggest that the PBR is involved in control of neuronal survival and gliosis after brain injury and identify this molecule as a potential target for neuroprotective interventions.