Ontogeny and the effects of in utero brain ischemia on interleukin-1β and interleukin-6 protein expression in ovine cerebral cortex and white matter

Analysis of genes differentially expressed in the cortex of mice with the Tbl1xr1Y446C/Y446C variant

Transducin β-like 1 X-linked receptor 1 (mouse Tbl1xr1) or TBL1X/Y related 1 (human TBL1XR1), part of the NCoR/SMRT corepressor complex, is involved in nuclear receptor signaling. Variants in TBL1XR1 cause a variety of neurodevelopmental disorders including Pierpont syndrome caused by the p.Tyr446Cys variant. We recently reported a mouse model carrying the Tbl1xr1Y446C/Y446C variant as a model for Pierpont syndrome. To obtain insight into mechanisms involved in altered brain development we studied gene expression patterns in the cortex of mutant and wild type (WT) mice, using RNA-sequencing, differentially expressed gene (DEG) analysis, gene set enrichment analysis (GSEA), weighted gene correlation network analysis (WGCNA) and hub gene analysis. We validated results in mutated mouse cortex, as well as in BV2 and SK-N-AS cell lines, in both of which Tbl1xr1 was knocked down by siRNA. Two DEGs (adj.P. Val < 0.05) were found in the cortex, Mpeg1 (downregulated in mutant mice) and 2900052N01Rik (upregulated in mutant mice). GSEA, WGCNA and hub gene analysis demonstrated changes in genes involved in ion channel function and neuroinflammation in the cortex of the Tbl1xr1Y446C/Y446C mice. The lowered expression of ion channel genes Kcnh3 and Kcnj4 mRNA was validated in the mutant mouse cortex, and increased expression of TRIM9, associated with neuroinflammation, was confirmed in the SK-N-AS cell line. Conclusively, our results show altered expression of genes involved in ion channel function and neuroinflammation in the cortex of the Tbl1xr1Y446C/Y446C mice. These may partly explain the impaired neurodevelopment observed in individuals with Pierpont syndrome and related TBL1XR1-related disorders.

L-ascorbyl-2-phosphate alleviates white matter injury caused by chronic hypoxia through the PRMT5/P53/NF-κB pathway

White matter injury (WMI) is one of the most serious complications associated with preterm births. Damage to oligodendrocytes, which are the key cells involved in WMI pathogenesis, can directly lead to myelin abnormalities. L-ascorbyl-2-phosphate (AS-2P) is a stable form of vitamin C. This study aimed to explore the protective effects of AS-2P against chronic hypoxia-induced WMI, and elucidate the underlying mechanisms. An in vivo chronic hypoxia model and in vitro oxygen-glucose deprivation (OGD) model were established to explore the effects of AS-2P on WMI using immunofluorescence, immunohistochemistry, western blotting, real-time quantitative polymerase chain reaction, Morris water maze test, novel object recognition test, beaming-walking test, electron microscopy, and flow cytometry. The results showed that AS-2P resulted in the increased expression of MBP, Olig2, PDGFRα and CC1, improved thickness and density of the myelin sheath, and reduced TNF-α expression and microglial cell infiltration to alleviate inflammation in the brain after chronic hypoxia. Moreover, AS-2P improved the memory, learning and motor abilities of the mice with WMI. These protective effects of AS-2P may involve the upregulation of protein arginine methyltransferase 5 (PRMT5) and downregulation of P53 and NF-κB. In conclusion, our study demonstrated that AS-2P attenuated chronic hypoxia-induced WMI in vivo and OGD-induced oligodendrocyte injury in vitro possibly by regulating the PRMT5/P53/NF-κB pathway, suggesting that AS-2P may be a potential therapeutic option for WMI.

Anti-Cytokine Therapy to Attenuate Ischemic-Reperfusion Associated Brain Injury in the Perinatal Period

Perinatal brain injury is a major cause of morbidity and long-standing disability in newborns. Hypothermia is the only therapy approved to attenuate brain injury in the newborn. However, this treatment is unfortunately only partially neuroprotective and can only be used to treat hypoxic-ischemic encephalopathy in full term infants. Therefore, there is an urgent need for adjunctive therapeutic strategies. Post-ischemic neuro-inflammation is a crucial contributor to the evolution of brain injury in neonates and constitutes a promising therapeutic target. Recently, we demonstrated encouraging neuroprotective capacities of anti-cytokine monoclonal antibodies (mAbs) in an ischemic-reperfusion (I/R) model of brain injury in the ovine fetus. The purpose of this review is to summarize the current knowledge regarding the inflammatory response in the perinatal sheep brain after I/R injury and to review our recent findings regarding the beneficial effects of treatment with anti-cytokine mAbs.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Alterations in inter-alpha inhibitor protein expression after hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is frequently associated with premature and/or full-term birth-related complications that reflect widespread damage to cerebral cortical structures. Inflammation has been implicated in the long-term evolution and severity of HI brain injury. Inter-Alpha Inhibitor Proteins (IAIPs) are immune modulator proteins that are reduced in systemic neonatal inflammatory states. We have shown that endogenous IAIPs are present in neurons, astrocytes and microglia and that exogenous treatment with human plasma purified IAIPs decreases neuronal injury and improves behavioral outcomes in neonatal rats with HI brain injury. In addition, we have shown that endogenous IAIPs are reduced in the brain of the ovine fetus shortly after ischemic injury. However, the effect of HI on changes in circulating and endogenous brain IAIPs has not been examined in neonatal rats. In the current study, we examined changes in endogenous IAIPs in the systemic circulation and brain of neonatal rats after exposure to HI brain injury. Postnatal day 7 rats were exposed to right carotid artery ligation and 8% oxygen for 2h. Sera were obtained immediately, 3, 12, 24, and 48h and brains 3 and 24h after HI. IAIPs levels were determined by a competitive enzyme-linked immunosorbent assay (ELISA) in sera and by Western immunoblots in cerebral cortices. Serum IAIPs were decreased 3h after HI and remained lower than in non-ischemic rats up to 7days after HI. IAIP expression increased in the ipsilateral cerebral cortices 24h after HI brain injury and in the hypoxic contralateral cortices. However, 3h after hypoxia alone the 250kDa IAIP moiety was reduced in the contralateral cortices. We speculate that changes in endogenous IAIPs levels in blood and brain represent constituents of endogenous anti-inflammatory neuroprotective mechanism(s) after HI in neonatal rats.

The significance of polymorphisms in genes encoding Il-1β, Il-6, TNFα, and Il-1RN in the pathogenesis of intraventricular hemorrhage in preterm infants

INTRODUCTION

Intraventricular hemorrhage (IVH) is a significant morbidity seen in very low birth weight infants. Genes related to inflammation may be risk factors for IVH.

MATERIAL AND METHODS

We examined five polymorphisms for an association with IVH in 100 preterm infants born from singleton pregnancy, before 32 + 0 weeks of gestation, exposed to antenatal steroid therapy, and without congenital abnormalities. These polymorphisms include interleukin-1β 3953 C>T, interleukin-6 -174G>C and -596G>A, tumor necrosis factor -308 G>A, and 86 bp variable number tandem repeat polymorphism of interleukin-1 receptor antagonist (Il -1RN 86 bp VNTR).

RESULTS

In our study population, 45 (45%) infants developed IVH, including 15 (33.33%) with stage 1, 19 (42.22%) with stage 2, 8 (17.77%) with stage 3, and 3 (6.66%) with stage 4. In contrast to the previously published data, the prevalence of IVH did not vary between infants with different IL-6 and TNFα alleles and genotypes. Our novel investigations in Il-1 +3953 C>T and Il-1RN 86 bp VNTR polymorphism did not show any significant link between those alleles or genotypes and IVH.

CONCLUSIONS

IVH is a significant problem for preterm infants. In addition to little progress in preventing IVH in preterm babies, substantial research that are focused on understanding the etiology, mechanism and risk factors for IVH are imperative. In the era of personalized medicine, identification of genetic risk factors creates opportunities to generate preventative strategies. Further studies should be performed to confirm the role of genetic factors in etiology and pathogenesis of IVH.

Neutralizing anti-interleukin-1β antibodies reduce ischemia-related interleukin-1β transport across the blood-brain barrier in fetal sheep

Hypoxic ischemic insults predispose to perinatal brain injury. Pro-inflammatory cytokines are important in the evolution of this injury. Interleukin-1β (IL-1β) is a key mediator of inflammatory responses and elevated IL-1β levels in brain correlate with adverse neurodevelopmental outcomes after brain injury. Impaired blood-brain barrier (BBB) function represents an important component of hypoxic-ischemic brain injury in the fetus. In addition, ischemia-reperfusion increases cytokine transport across the BBB of the ovine fetus. Reducing pro-inflammatory cytokine entry into brain could represent a novel approach to attenuate ischemia-related brain injury. We hypothesized that infusions of neutralizing IL-1β monoclonal antibody (mAb) reduce IL-1β transport across the BBB after ischemia in the fetus. Fetal sheep were studied 24-h after 30-min of carotid artery occlusion. Fetuses were treated with placebo- or anti-IL-1β mAb intravenously 15-min and 4-h after ischemia. Ovine IL-1β protein expressed from IL-1β pGEX-2T vectors in Escherichia coli (E. coli) BL-21 cells was produced, purified, and radiolabeled with ¹²⁵I. BBB permeability was quantified using the blood-to-brain transfer constant (K_i) with ¹²⁵I-radiolabeled-IL-1β. Increases in anti-IL-1β mAb were observed in the brain of the mAb-treated group (P<0.001). Blood-to-brain transport of ¹²⁵I-IL-1β was lower (P<0.04) across brain regions in the anti-IL-1β mAb-treated than placebo-treated ischemic fetuses. Plasma ¹²⁵I-IL-1β counts were higher (P<0.001) in the anti-IL-1β mAb- than placebo-treated ischemic fetuses. Systemic infusions of anti-IL-1β mAb reduce IL-1β transport across the BBB after ischemia in the ovine fetus. Our findings suggest that conditions associated with increases in systemic pro-inflammatory cytokines and neurodevelopmental impairment could benefit from an anti-cytokine therapeutic strategy.

Ischemia reduces inter-alpha inhibitor proteins in the brain of the ovine fetus

Hypoxic-ischemic (HI) brain injury is a major cause of neurological abnormalities in the perinatal period. Inflammation contributes to the evolution of HI brain injury. Inter-alpha inhibitor proteins (IAIPs) are a family of proteins that are part of the innate immune system. We have reported that endogenous IAIPs exhibit developmental changes in ovine brain and that exogenous IAIP treatment reduces neuronal death in HI neonatal rats. However, the effects of HI on endogenous IAIPs in brain have not been previously examined. In this study, we examined the effects of ischemia-reperfusion on endogenous IAIPs levels in fetal sheep brain. Cerebral cortex, cerebellum, cervical spinal cord, choroid plexus, and CSF were snap frozen from sham control fetuses at 127 days gestation and after 30-min of carotid occlusion and 4-, 24-, and 48-h of reperfusion. IAIP levels were determined by Western immunoblot. IAIP expressions of the 250 kDa Inter-alpha inhibitor (IaI) and 125 kDa Pre-alpha inhibitor (PaI) in cerebral cortex and PaI in cerebellum were reduced (p < 0.05) 4-h after ischemia compared with controls and returned toward control levels 24- and 48-h after ischemia. CSF PaI and IaI were reduced 48 h after ischemia. We conclude that IAIPs in cerebral cortex and cerebellum are reduced by brain ischemia, and return toward control levels between 24 and 48 h after ischemia. However, changes in CSF IAIPs were delayed, exhibiting decreases 48 h after ischemia. We speculate that the decreases in endogenous IAIPs reflect increased utilization, potentially suggesting that they have endogenous neuroprotective properties. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 726-737, 2017.

HMGB1 Translocation After Ischemia in the Ovine Fetal Brain

Inflammation contributes to the evolution of hypoxic-ischemic (HI) brain injury. High-mobility group box-1 (HMGB1) is a nuclear protein that is translocated from the nucleus and released after ischemia in adult rodents and thereby initiates inflammatory responses. However, there is very little information regarding the effects of HI on HMGB1 in immature brains. To investigate the effects of HI on HMGB1 in the term-equivalent fetal brain, ovine fetuses at 127 days gestation were studied after 30 minutes of carotid occlusion. Groups were sham-control and ischemia with 48 hours and ischemia with 72 hours of reperfusion. By immunohistochemistry, HMGB1 was found to be localized primarily in cell nuclei and partially in cytoplasmic compartments in the cerebral cortex of controls. Ischemia increased the area fraction of neuronal cells with cytoplasmic HMGB1 staining, and Western immunoblot revealed that cytosolic HMGB1 expression increased after ischemia (p < 0.05) and decreased in nuclei in ischemic versus the sham-control brains (p < 0.05). These data indicate that HMGB1 translocates from the nuclear to cytosolic compartments after ischemic brain injury in fetal sheep. This translocation may enable the action of HMGB1 as a proinflammatory cytokine that contributes to HI injury in the developing brain.

Ontogeny of tight junction protein expression in the ovine cerebral cortex during development

Tight junctions of the blood-brain barrier are composed of transmembrane and associated cytoplasmic proteins. The transmembrane claudin proteins form the primary seal between endothelial cells and junctional adhesion molecules (JAMs) regulate tight junction formation. We have previously shown that claudin-1, claudin-5, zonula occludens (ZO)-1, and ZO-2 exhibit differential developmental regulation from 60% of gestation up to maturity in adult sheep. The purpose of the current study was to examine developmental changes in claudin-3, -12, and JAM-A protein expression in cerebral cortices of fetuses at 60%, 80%, and 90% gestation, and in newborn and adult sheep. We also examined correlations between changes in endogenous cortisol levels and tight junction protein expression in cerebral cortices of the fetuses. Claudin-3, -12 and JAM-A expressions were determined by Western immunoblot. Claudin-3 and -12 were lower (P<0.01) at 60%, 80%, 90% and in newborns than in adults, and JAM-A was lower in adults than in fetuses at 80% and 90% gestation. Claudin-3 expression demonstrated a direct correlation with increasing plasma cortisol levels (r=0.60, n=15, P<0.02) in the fetuses. We conclude that: claudin-3, -12 and JAM-A are expressed as early as 60% of gestation in ovine cerebral cortices, exhibit differential developmental regulation, and that increasing endogenous glucocorticoids modulate claudin-3 expression in the fetus.

Interleukin-1β transfer across the blood-brain barrier in the ovine fetus

Pro-inflammatory cytokines contribute to hypoxic-ischemic brain injury. Blood-brain barrier (BBB) dysfunction represents an important component of hypoxic-ischemic brain injury in the fetus. Hypoxic-ischemic injury could accentuate systemic cytokine transfer across the fetal BBB. There has been considerable conjecture suggesting that systemic cytokines could cross the BBB during the perinatal period. Nonetheless, evidence to support this contention is sparse. We hypothesized that ischemia-reperfusion increases the transfer of systemic interleukin-1β (IL-1β) across the BBB in the fetus. Ovine fetuses at 127 days of gestation were studied 4 hours after 30 minutes of bilateral carotid artery occlusion and compared with a nonischemic group. Recombinant ovine IL-1β protein was expressed from an IL-1β pGEX-2 T vector in E. coli BL-21 cells and purified. The BBB function was quantified in 12 brain regions using a blood-to-brain transfer constant with intravenous (125)I-radiolabeled IL-1β ((125)I-IL-1β). Interleukin-1β crossed the intact BBB in nonischemic fetuses. Blood-to-brain transport of (125)I-IL-1β was higher (P<0.05) across brain regions in fetuses exposed to ischemia-reperfusion than nonischemic fetuses. We conclude that systemic IL-1β crosses the intact fetal BBB, and that ischemia-reperfusion increases transfer of this cytokine across the fetal BBB. Therefore, altered BBB function after hypoxia-ischemia facilitates entry of systemic cytokines into the brain of the fetus.

Anti-IL-6 neutralizing antibody modulates blood-brain barrier function in the ovine fetus

Impaired blood-brain barrier function represents an important component of hypoxic-ischemic brain injury in the perinatal period. Proinflammatory cytokines could contribute to ischemia-related blood-brain barrier dysfunction. IL-6 increases vascular endothelial cell monolayer permeability in vitro. However, contributions of IL-6 to blood-brain barrier abnormalities have not been examined in the immature brain in vivo. We generated pharmacologic quantities of ovine-specific neutralizing anti-IL-6 mAbs and systemically infused mAbs into fetal sheep at 126 days of gestation after exposure to brain ischemia. Anti-IL-6 mAbs were measured by ELISA in fetal plasma, cerebral cortex, and cerebrospinal fluid, blood-brain barrier permeability was quantified using the blood-to-brain transfer constant in brain regions, and IL-6, tight junction proteins, and plasmalemma vesicle protein (PLVAP) were detected by Western immunoblot. Anti-IL-6 mAb infusions resulted in increases in mAb (P < 0.05) in plasma, brain parenchyma, and cerebrospinal fluid and decreases in brain IL-6 protein. Twenty-four hours after ischemia, anti-IL-6 mAb infusions attenuated ischemia-related increases in blood-brain barrier permeability and modulated tight junction and PLVAP protein expression in fetal brain. We conclude that inhibiting the effects of IL-6 protein with systemic infusions of neutralizing antibodies attenuates ischemia-related increases in blood-brain barrier permeability by inhibiting IL-6 and modulates tight junction proteins after ischemia.

Neutralizing anti-interleukin-1β antibodies modulate fetal blood-brain barrier function after ischemia

We have previously shown that increases in blood-brain barrier permeability represent an important component of ischemia-reperfusion related brain injury in the fetus. Pro-inflammatory cytokines could contribute to these abnormalities in blood-brain barrier function. We have generated pharmacological quantities of mouse anti-ovine interleukin-1β monoclonal antibody and shown that this antibody has very high sensitivity and specificity for interleukin-1β protein. This antibody also neutralizes the effects of interleukin-1β protein in vitro. In the current study, we hypothesized that the neutralizing anti-interleukin-1β monoclonal antibody attenuates ischemia-reperfusion related fetal blood-brain barrier dysfunction. Instrumented ovine fetuses at 127 days of gestation were studied after 30 min of carotid occlusion and 24h of reperfusion. Groups were sham operated placebo-control- (n=5), ischemia-placebo- (n=6), ischemia-anti-IL-1β antibody- (n=7), and sham-control antibody- (n=2) treated animals. Systemic infusions of placebo (0.154M NaCl) or anti-interleukin-1β monoclonal antibody (5.1±0.6 mg/kg) were given intravenously to the same sham or ischemic group of fetuses at 15 min and 4h after ischemia. Concentrations of interleukin-1β protein and anti-interleukin-1β monoclonal antibody were measured by ELISA in fetal plasma, cerebrospinal fluid, and parietal cerebral cortex. Blood-brain barrier permeability was quantified using the blood-to-brain transfer constant (Ki) with α-aminoisobutyric acid in multiple brain regions. Interleukin-1β protein was also measured in parietal cerebral cortices and tight junction proteins in multiple brain regions by Western immunoblot. Cerebral cortical interleukin-1β protein increased (P<0.001) after ischemia-reperfusion. After anti-interleukin-1β monoclonal antibody infusions, plasma anti-interleukin-1β monoclonal antibody was elevated (P<0.001), brain anti-interleukin-1β monoclonal antibody levels were higher (P<0.03), and interleukin-1β protein concentrations (P<0.03) and protein expressions (P<0.001) were lower in the monoclonal antibody-treated group than in placebo-treated-ischemia-reperfusion group. Monoclonal antibody infusions attenuated ischemia-reperfusion-related increases in Ki across the brain regions (P<0.04), and Ki showed an inverse linear correlation (r= -0.65, P<0.02) with anti-interleukin-1β monoclonal antibody concentrations in the parietal cortex, but had little effect on tight junction protein expression. We conclude that systemic anti-interleukin-1β monoclonal antibody infusions after ischemia result in brain anti-interleukin-1β antibody uptake, and attenuate ischemia-reperfusion-related interleukin-1β protein up-regulation and increases in blood-brain barrier permeability across brain regions in the fetus. The pro-inflammatory cytokine, interleukin-1β, contributes to impaired blood-brain barrier function after ischemia in the fetus.

Exploiting ovine immunology to improve the relevance of biomedical models

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Sheep make a valuable contribution to immunology research.

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Lessons to be learned from studying infections in the natural host.

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Factors to consider when selecting biomedical models.

Animal models of human disease are important tools in many areas of biomedicine; for example, in infectious disease research and in the development of novel drugs and medical devices. Most studies involving animals use rodents, in particular congenic mice, due to the availability of a wide number of strains and the ease with which they can be genetically manipulated. The use of mouse models has led to major advances in many fields of research, in particular in immunology but despite these advances, no animal model can exactly reproduce all the features of human disease. It is increasingly becoming recognised that in many circumstances mice do not provide the best model and that alternative species may be more appropriate. Here, we describe the relative merits of sheep as biomedical models for human physiology and disease in comparison to mice, with a particular focus on reproductive and respiratory pathogens.

Pathophysiology of glia in perinatal white matter injury

Injury to the preterm brain has a particular predilection for cerebral white matter. White matter injury (WMI) is the most common cause of brain injury in preterm infants and a major cause of chronic neurological morbidity including cerebral palsy. Factors that predispose to WMI include cerebral oxygenation disturbances and maternal-fetal infection. During the acute phase of WMI, pronounced oxidative damage occurs that targets late oligodendrocyte progenitors (pre-OLs). The developmental predilection for WMI to occur during prematurity appears to be related to both the timing of appearance and regional distribution of susceptible pre-OLs that are vulnerable to a variety of chemical mediators including reactive oxygen species, glutamate, cytokines, and adenosine. During the chronic phase of WMI, the white matter displays abberant regeneration and repair responses. Early OL progenitors respond to WMI with a rapid robust proliferative response that results in a several fold regeneration of pre-OLs that fail to terminally differentiate along their normal developmental time course. Pre-OL maturation arrest appears to be related in part to inhibitory factors that derive from reactive astrocytes in chronic lesions. Recent high field magnetic resonance imaging (MRI) data support that three distinct forms of chronic WMI exist, each of which displays unique MRI and histopathological features. These findings suggest the possibility that therapies directed at myelin regeneration and repair could be initiated early after WMI and monitored over time. These new mechanisms of acute and chronic WMI provide access to a variety of new strategies to prevent or promote repair of WMI in premature infants.

Gene-environment interactions in severe intraventricular hemorrhage of preterm neonates

Intraventricular hemorrhage (IVH) of the preterm neonate is a complex developmental disorder, with contributions from both the environment and the genome. IVH, or hemorrhage into the germinal matrix of the developing brain with secondary periventricular infarction, occurs in that critical period of time before the 32nd to 33rd wk postconception and has been attributed to changes in cerebral blood flow to the immature germinal matrix microvasculature. Emerging data suggest that genes subserving coagulation, inflammatory, and vascular pathways and their interactions with environmental triggers may influence both the incidence and severity of cerebral injury and are the subject of this review. Polymorphisms in the Factor V Leiden gene are associated with the atypical timing of IVH, suggesting an as yet unknown environmental trigger. The methylenetetrahydrofolate reductase (MTHFR) variants render neonates more vulnerable to cerebral injury in the presence of perinatal hypoxia. The present study demonstrates that the MTHFR 677C>T polymorphism and low 5-min Apgar score additively increase the risk of IVH. Finally, review of published preclinical data suggests the stressors of delivery result in hemorrhage in the presence of mutations in collagen 4A1, a major structural protein of the developing cerebral vasculature. Maternal genetics and fetal environment may also play a role.

Role of endogenous IL-6 in the neonatal expansion and functionality of Wistar rat pancreatic alpha cells

AIMS/HYPOTHESIS

Plasma glucagon concentrations rise sharply during the early postnatal period. This condition is associated with increased alpha cell mass. However, the trophic factors that regulate alpha cell turnover during the perinatal period have not been studied. Macrophage infiltrations are present in the neonatal pancreas, and this cell type releases cytokines such as IL-6. Alpha cells have been identified as a primary target of IL-6 actions. We therefore investigated the physiological relevance of IL-6 to neonatal pancreatic alpha cell maturation.

METHODS

Histochemical analyses were performed to quantify alpha cell mass, replication and apoptosis. Pancreatic Il6 expression was determined by quantitative RT-PCR. The biological effect of IL-6 was tested in two in vivo rat models of IL-6 blockade and chronic undernutrition.

RESULTS

Alpha cell mass increased sharply shortly after birth but decreased significantly after weaning. Pancreatic alpha cell proliferation was as high as 2.5% at the beginning of suckling but diminished with time to 1.2% in adulthood. Similarly, alpha cell neoformation was remarkably high on postnatal day (PN) 4, whereas alpha cell apoptosis was low throughout the neonatal period. Moreover, Il6 mRNA exhibited developmental upregulation in the pancreas of suckling rats, with the highest expression on PN2. Neutralisation of IL-6 reduced alpha cell mass expansion and glucagon production. IL-6 staining was detected within the islets, mainly in the alpha cells. Finally, undernourished neonates showed altered alpha cell number and function and delayed appearance of IL-6 in the pancreas.

CONCLUSIONS/INTERPRETATION

These data point to a potential role for local IL-6 in the regulation of alpha cell growth and function during suckling.