Social Environment Ameliorates Behavioral and Immune Impairments in Tyrosine Hydroxylase Haploinsufficient Female Mice

The social environment can influence the functional capacity of nervous and immune systems, and consequently the state of health, especially in aged individuals. Adult female tyrosine hydroxylase haploinsufficient (TH-HZ) mice exhibit behavioral impairments, premature immunosenescence and oxidative- inflammatory stress. All these deteriorations are associated with a lower lifespan than wild type (WT) counterparts. The aim was to analyze whether the cohabitation with WT animals could revert or at least ameliorate the deterioration in the nervous and immune systems that female TH-HZ mice show at adult age. Female TH-HZ and WT mice at age of 3-4 weeks were divided into following groups: control TH-HZ (5 TH-HZ mice in the cage; TH-HZ100%), control WT (5 WT mice in the cage; WT100%), TH-HZ > 50% and WT < 50% (5 TH-HZ with 2 WT mice in each cage) as well as TH-HZ < 50% and WT > 50% (2 TH-HZ and 5 WT mice in each cage). At the age of 37-38 weeks, all mice were submitted to a battery of behavioral tests, evaluating sensorimotor abilities, exploratory capacities and anxiety-like behaviors. Subsequently, peritoneal leukocytes were extracted and several immune functions as well as oxidative and inflammatory stress parameters were analyzed. The results showed that the TH-HZ < 50% group had improved behavioral responses, especially anxiety-like behaviors, and the immunosenescence and oxidative stress of their peritoneal leukocytes were ameliorated. However, WT mice that cohabited with TH-HZ mice presented higher anxiety-like behaviors and deterioration in immune functions and in their inflammatory stress parameters. Thus, this social environment is capable of ameliorating the impairments associated with a haploinsufficiency of the th gene. Graphical Abstract.

Balance of pro-apoptotic transforming growth factor-β and anti-apoptotic insulin effects in the control of cell death in the postnatal mouse retina

Transforming growth factor (TGF)-beta and insulin display opposite effects in regulating programmed cell death during vertebrate retina development; the former induces apoptosis while the latter prevents it. In the present study we investigated coordinated actions of TGF-beta and insulin in an organotypic culture system of early postnatal mouse retina. Addition of exogenous TGF-beta resulted in a significant increase in cell death whereas exogenous insulin attenuated apoptosis and was capable of blocking TGF-beta-induced apoptosis. This effect appeared to be modulated via insulin-induced transcriptional down-regulation of TGF-beta receptor II levels. The analysis of downstream signalling molecules also revealed opposite effects of both factors; insulin provided survival signalling by increasing the level of anti-apoptotic Bcl-2 protein expression and phosphorylation and down-regulating caspase 3 activity whereas pro-apoptotic TGF-beta signalling reduced Bcl-2 mRNA levels and Bcl-2 phosphorylation and induced the expression of TGF-induced immediate-early gene (TIEG), a Krüppel-like zinc-finger transcription factor, mimicking TGF-beta activity.

Insulin-like growth factor 1 is required for survival of transit-amplifying neuroblasts and differentiation of otic neurons

Neurons that connect mechanosensory hair cell receptors to the central nervous system derive from the otic vesicle from where otic neuroblasts delaminate and form the cochleovestibular ganglion (CVG). Local signals interact to promote this process, which is autonomous and intrinsic to the otic vesicle. We have studied the expression and activity of insulin-like growth factor-1 (IGF-1) during the formation of the chick CVG, focusing attention on its role in neurogenesis. IGF-1 and its receptor (IGFR) were detected at the mRNA and protein levels in the otic epithelium and the CVG. The function of IGF-1 was explored in explants of otic vesicle by assessing the formation of the CVG in the presence of anti-IGF-1 antibodies or the receptor competitive antagonist JB1. Interference with IGF-1 activity inhibited CVG formation in growth factor-free media, revealing that endogenous IGF-1 activity is essential for ganglion generation. Analysis of cell proliferation cell death, and expression of the early neuronal antigens Tuj-1, Islet-1/2, and G4 indicated that IGF-1 was required for survival, proliferation, and differentiation of an actively expanding population of otic neuroblasts. IGF-1 blockade, however, did not affect NeuroD within the otic epithelium. Experiments carried out on isolated CVG showed that exogenous IGF-1 induced cell proliferation, neurite outgrowth, and G4 expression. These effects of IGF-1 were blocked by JB1. These findings suggest that IGF-1 is essential for neurogenesis by allowing the expansion of a transit-amplifying neuroblast population and its differentiation into postmitotic neurons. IGF-1 is one of the signals underlying autonomous development of the otic vesicle.

Molecular scanning for mutations in the insulin receptor substrate-1 (IRS-1) gene in Mexican Americans with Type 2 diabetes mellitus

BACKGROUND

Insulin receptor substrate-1 (IRS-1) is an endogenous substrate for the insulin receptor tyrosine kinase, which plays an important role in insulin signaling. Mutations in the IRS-1 gene are associated in some populations with obesity and Type 2 diabetes.

METHODS

To determine whether variation in the IRS-1 gene contributes to genetic susceptibility to insulin resistance and Type 2 diabetes in Mexican Americans, the entire coding region of the IRS-1 gene was screened for variation in 31 unrelated subjects with Type 2 diabetes using single-stranded conformational polymorphism analysis (SSCP) and dideoxy sequence analysis. Variants encoding amino acid substitutions were genotyped in 27 unrelated nondiabetic Mexican Americans and in all family members of subjects containing these variants, and association analyses were performed. To trace the ancestral origins of the variants, Iberian Caucasians and Pima Indians were also genotyped.

RESULTS

Eight single base changes were found: four silent polymorphisms and four missense mutations (Ala94Thr, Ala512Pro, Ser892Gly and Gly971Arg). Allele frequencies were 0.009, 0.017, 0.017 and 0.043, respectively. There were no significant associations of any of these variants with diabetes, glucose or insulin levels during an oral glucose tolerance test, or with body mass index (BMI) in Mexican American families except for a modest association between the Ala94Thr variant and decreased BMI (30.4 kg/m(2) vs 24.0 kg/m(2); p=0.035). None of these four missense mutations were detected in Pima Indians. In Iberian Caucasians, neither Ala94Thr nor Ser892Gly were detected, and Ala512Pro was detected in only 0/60 diabetic patients and 1/60 nondiabetic controls. Gly971Arg was relatively more common in Iberian Caucasians with 12/58 diabetic patients and 7/60 nondiabetic controls being heterozygous for this variant (p=0.21 for comparison between diabetic and nondiabetic subjects).

CONCLUSIONS

Ala94Thr, Ala512Pro and Ser892Gly mutation are rare in the populations studied. Gly971Arg, is more common in Mexican Americans and Caucasians, but is not a major contributor to genetic susceptibility to Type 2 diabetes.

c-Raf regulates cell survival and retinal ganglion cell morphogenesis during neurogenesis

The signaling cascade Ras/Raf/mitogen-activated protein kinases modulates cell proliferation, differentiation, and survival, all key cellular processes during neural development. To better define the in vivo role of Raf during chick retinal neurogenesis, we interfered with Raf-dependent signaling during days 4.5 to 7.5 of embryonic development by expressing a dominant negative mutant of c-Raf (DeltaRaf), which blocks Ras-dependent Raf activation, and by overexpressing wild-type c-Raf. DeltaRaf expression induced an increase in cell death by apoptosis, whereas it did not affect overall cell proliferation and differentiation. In parallel, the number of Islet-1/2-positive and TUJ1-positive retinal ganglion cells were diminished in their definitive layer, whereas there was an increase in the number of mislocated Islet-1/2-positive cells. This disturbed morphogenesis correlated with a disruption of the optic fiber layer. Conversely, c-Raf overexpression caused moderate opposite effects on apoptosis. These results frame in vivo early neurogenesis processes in which c-Raf is essential.

In vivo regulation of cell death by embryonic (pro)insulin and the insulin receptor during early retinal neurogenesis

Programmed cell death is an established developmental process in the nervous system. Whereas the regulation and the developmental role of neuronal cell death have been widely demonstrated, the relevance of cell death during early neurogenesis, the cells affected and the identity of regulatory local growth factors remain poorly characterized. We have previously described specific in vivo patterns of apoptosis during early retinal neurogenesis, and that exogenous insulin acts as survival factor (Diaz, B., Pimentel, B., De Pablo, F. and de la Rosa, E. J. (1999) Eur. J. Neurosci. 11, 1624–1632). Proinsulin mRNA was found to be expressed broadly in the early embryonic chick retina, and decreased later between days 6 and 8 of embryonic development, when there was increased expression of insulin-like growth factor I mRNA, absent or very scarce at earlier stages. Consequently, we studied whether proinsulin and/or insulin ((pro)insulin) action in prevention of cell death has physiological relevance during early neural development. In ovo treatment at day 2 of embryonic development with specific antibodies against (pro)insulin or the insulin receptor induced apoptosis in the neuroretina. The distribution of apoptotic cells two days after the blockade was similar to naturally occurring cell death, as visualized by TdT-mediated dUTP nick end labeling. The apoptosis induced by the insulin receptor blockade preferentially affected to the Islet1/2 positive cells, that is, the differentiated retinal ganglion cells. In parallel, the insulin survival effect on cultured retinas correlated with the activation of Akt to a greater extent than with the activation of MAP kinase. These results suggest that the physiological cell death occurring in early stages of retinal development is regulated by locally produced (pro)insulin through the activation of the Akt survival pathway.

DNA binding factors which interact with the Sp1 site of the chicken delta 1-crystallin promoter are developmentally regulated

Transcription of the delta 1-crystallin gene is developmentally regulated in the embryonic chicken lens. Previous work defined a positive transcription regulatory element between positions -120 and -43 of the delta 1-crystallin promoter. This region contains a putative Sp1 binding site (-78 to -71), adjacent to a CAAT box (-70 to -67). Gel retardation assays using lens nuclear extracts revealed two protein-DNA complexes which involved the Sp1 site. The formation of the complexes increased from day 6 to day 11 of embryogenesis (period of lens organogenesis) peaked between days 11 and 15, then decreased in a non-parallel manner until hatching (day 21). A point mutation in the Sp1 binding site of the delta 1-crystallin promoter abolished formation of one of the complexes (complex 1, slower in mobility), while point mutations in the CAAT box had no effect on the formation of either complex. Studies using purified Sp1 protein and increasing amounts of embryonic chicken lens nuclear extracts showed cooperativity in the formation of both complexes, more remarkable with complex 1.

Insulin-like growth factor-I and insulin as growth and differentiation factors in chicken embryogenesis

The avian embryo has been a useful model system for studies on the role of insulin and its close relative insulin-like growth factor-I (IGF-I) in development. The unfertilized chicken egg contains both peptides from maternal origin, and the embryo expresses insulin and IGF-I before the major organs are formed. Insulin receptors and IGF-I receptors are found in the blastoderm and in all tissues examined during organogenesis. When exogenous insulin or IGF-I are added to the embryo, growth and differentiation events are stimulated. By contrast, insulin antibodies and insulin receptor antibodies retard embryo development. In embryos cultured ex ovo, in which growth is impaired, the levels of serum IGF-I are decreased.

Insulin action in early embryonic life: anti-insulin receptor antibodies retard chicken embryo growth but not muscle differentiation in vivo

Insulin receptors are present in chicken embryos at day 2 of development and insulin stimulates embryonic growth and differentiation. Most important, anti-insulin antibodies cause either death or developmental retardation in chicken embryos of that age. To determine if the embryo's endogenous insulin acts through its own receptor, we compared the effects of anti-insulin antibodies to the effects of anti-insulin receptor antibodies on growth and differentiation indexes in the chicken embryo. While the anti-insulin antibody caused a dose-dependent decrease in growth parameters like weight, total protein, DNA, RNA, total creatine kinase activity and a marker of differentiation, the creatine kinase-MB, the anti-insulin receptor antibody decreased all parameters except the creatine kinase-MB. Many, but not all, of the effects of insulin in early embryos, thus, are mediated through the insulin receptor.

Insulin is present in chicken eggs and early chick embryos

We showed that insulin appears in the chick embryo before beta-cells are recognizable, as well as in the egg constituents even before fertilization. Acid-ethanol extracts of 2- to 8-day-old embryos were gel-filtered on Sephadex G-50. The peak of immunoreactive insulin chromatographed in a position corresponding to that of authentic insulin. The immunoreactive insulin extracted from embryos was approximately 2 ng/g wet wt during early embryogenesis (days 2, 3, and 4), with a 2- to 3- fold increase by days 5 and 6, in conjunction with pancreatic development. The heads of the embryos contributed 22-23% of the total insulin on days 3 and 4, but only 5% by day 5. Based on its reactivity in a pork insulin RIA, chicken insulin RIA, and rat adipocyte bioassay, we concluded that the material is very similar to avian (chicken or turkey) rather than mammalian type insulin. Similar immunological and biological insulin-like activity [but at much lower concentrations (0.2-0.8 ng/ml)] were recovered from the gel-filtered acid-ethanol extracts of yolk and white of unfertilized and fertilized eggs. This study, which shows that insulin is present at a very early stage in ontogeny, extends observations that insulin is native to organisms that lack pancreatic islets, including flies, worms, and microbes.