Rolf Zetterström

An orphan nuclear receptor activated by pregnanes defines a novel steroid signaling pathway.

Steroid hormones exert profound effects on differentiation, development, and homeostasis in higher eukaryotes through interactions with nuclear receptors. We describe a novel orphan nuclear receptor, termed the pregnane X receptor (PXR), that is activated by naturally occurring steroids such as pregnenolone and progesterone, and synthetic glucocorticoids and antiglucocorticoids. PXR exists as two isoforms, PXR.1 and PXR.2, that are differentially activated by steroids. Notably, PXR.1 is efficaciously activated by pregnenolone 16alpha-carbonitrile, a glucocorticoid receptor antagonist that induces the expression of the CYP3A family of steroid hydroxylases and modulates sterol and bile acid biosynthesis in vivo. Our results provide evidence for the existence of a novel steroid hormone signaling pathway with potential implications in the regulation of steroid hormone and sterol homeostasis.

Cellular expression of the immediate early transcription factors Nurr1 and NGFI-B suggests a gene regulatory role in several brain regions including the nigrostriatal dopamine system.

Nurr1 and NGFI-B are closely related orphan members of the steroid-thyroid hormone receptor family involved in immediate early responses to stimuli such as growth factors. In-situ hybridization in the developing and adult mouse and rat demonstrated Nurr1 mRNA in several regions during early central nervous system (CNS) development. Expression persisted through the pre- and postnatal periods and was also found in several areas in the adult CNS. Positive areas include the olfactory bulb, parts of the cortex, the hippocampal formation and substantia nigra where Nurr1 and tyrosine hydroxylase mRNAs were co-expressed. 6-Hydroxydopamine-induced degeneration of mesencephalic dopamine neurons led to a corresponding loss of Nurr1 mRNA, demonstrating a link between Nurr1 and dopaminergic neurons. NGFI-B mRNA was not found in the prenatal CNS but was highly expressed in the adult brain in many areas including the olfactory bulb, cortex, basal ganglia and hippocampus. The spatiotemporal distribution of Nurr1 and NGFI-B mRNAs suggests that these transcription factors are involved in the development and maturation of specific sets of CNS neurons. The experimental data imply that one of these functions may be to control gene regulatory events important for development and function of those neurons that degenerate in patients with Parkinsons disease.

Role of retinoids in the CNS: differential expression of retinoid binding proteins and receptors and evidence for presence of retinoic acid

Retinoic acid (RA), a retinoid metabolite, acts as a gene regulator via ligand‐activated transcription factors, known as retinoic acid receptors (RARs) and retinoid X receptors (RXRs), both existing in three different subtypes, α, β and γ. In the intracellular regulation of retinoids, four binding proteins have been implicated: cellular retinol binding protein (CRBP) types I and II and cellular retinoic acid binding protein (CRABP) types I and II. We have used in situ hybridization to localize mRNA species encoding CRBP‐ and CRABP I and II as well as all the different nuclear receptors in the developing and adult rat and mouse central nervous system (CNS), an assay to investigate the possible presence of RA, and immunohistochemistry to also analyse CRBP I‐ and CRABP Iimmunoreactivity (IR). RXRβ is found in most areas while RARα and ‐β and RXRα and ‐γ show much more restricted patterns of expression. RARα is found in cortex and hippocampus and RARβ and RXRγ are both highly expressed in the dopamine‐innervated areas caudate/putamen, nucleus accumbens and olfactory tubercle. RARγ could not be detected in any part of the CNS. Using an in vitro reporter assay, we found high levels of RA in the developing striatum. The caudate/putamen of the developing brain showed strong CRBP I‐IR in a compartmentalized manner, while at the same time containing many evenly distributed CRABP I‐IR neurons. The CRBP I‐ and CRABP I‐IR patterns were closely paralleled by the presence of the corresponding transcripts. The specific expression pattern of retinoid‐binding proteins and nuclear retinoid receptors as well as the presence of RA in striatum suggests that retinoids are important in many brain structures and emphasizes a role for retinoids in gene regulatory events in postnatal and adult striatum.

Retinoid-X receptor signalling in the developing spinal cord

Retinoids regulate gene expression through the action of retinoic acid receptors (RARs) and retinoid-X receptors (RXRs), which both belong to the family of nuclear hormone receptors,. Retinoids are of fundamental importance during development, but it has been difficult to assess the distribution of ligand-activated receptors in vivo. This is particularly the case for RXR, which is a critical unliganded auxiliary protein for several nuclear receptors, including RAR, but its ligand-activated role in vivo remains uncertain. Here we describe an assay in transgenic mice, based on the expression of an effector fusion protein linking the ligand-binding domain of either RXR or RAR to the yeast Gal4 DNA-binding domain, and the in situ detection of ligand-activated effector proteins by using an inducible transgenic lacZ reporter gene. We detect receptor activation in the spinal cord in a pattern that indicates that the receptor functions in the maturation of limb-innervating motor neurons. Our results reveal a specific activation pattern of Gal4–RXR which indicates that RXR is a critical bona fide receptor in the developing spinal cord.

Orphan nuclear receptor Nurr1 is essential for Ret expression in midbrain dopamine neurons and in the brain stem.

The orphan nuclear receptor Nurr1 is essential for development of midbrain dopamine (DA) cells. In Nurr1-deficient mice, DA precursor cells fail to migrate normally, are unable to innervate target areas, and only transiently express DA cell marker genes. In the search for Nurr1-regulated genes that might explain this developmental phenotype, we found that expression of the receptor tyrosine kinase Ret is deregulated in these cells of Nurr1-deficient embryos. In addition, our analyses establish Nurr1 as an early marker for the dorsal motor nucleus (DMN) of the vagus nerve. Interestingly, Ret expression is absent also in these cells in Nurr1-targeted mice. Neuronal innervation of vagus nerve target areas appeared normal apart from a subtle disorganization of the DMN-derived nerve fibers. In conclusion, regulation of Ret by Nurr1 in midbrain DA neurons and in the DMN has implications for both embryonal development and adult physiology in which signaling by neurotrophic factors plays important roles.

Localization of cellular retinoid-binding proteins suggests specific roles for retinoids in the adult central nervous system

Retinoic acid, the active metabolite of retinoids (vitamin A compounds), is thought to act as a gene regulator via ligand-activated transcription factors. In order to investigate possible roles of retinoids and retinoid-controlled gene expression in brain function, we have used immunohistochemistry to localize the possible presence of two intracellular retinoid-binding proteins, cellular retinol-binding protein type I and cellular retinoic acid-binding protein type I, in the adult rat central nervous system. We find a widespread, yet distinct, presence of these two binding proteins in the brain and spinal cord. Most of the immunoreactivity is neuronal, including cell somata, as well as dendritic and axonal processes and axon terminals. Cellular retinol-binding protein type I-immunoreactivity is also found in the walls of cerebral blood vessels, the meninges, the choroid plexus, certain ependymal cells, tanocytes and certain other glial elements. The cellular retinol-binding protein type I- and cellular retinoic acid-binding protein type I-immunoreactivity patterns appear to be almost exclusively non-overlapping. Very strong cellular retinol-binding protein type I-immunoreactivity is found in the dendritic layers of the hippocampal formation and dentate gyrus. Cellular retinol-binding protein type I-immunoreactivity is also present in layer 5 cortical pyramidal neurons and neurons in the glomerular layer of the olfactory bulb. Many other areas, e.g. hypothalamic nuclei and amygdala areas, contain networks of varicose cellular retinol-binding protein type I-immunoreactive nerve fibers. The medial amygdaloid nucleus contains strongly cellular retinol-binding protein type I-positive neurons. Cellular retinoic acid-binding protein type I-immunoreactivity is more restricted in the adult brain. Strong cellular retinoic acid-binding protein type I-immunoreactivity is, however, found in a population of medium-sized neurons scattered throughout the striatum, in neurons in the glomerular layer of the olfactory bulb, the olfactory nerve and in a group of nerve cells close to the third ventricle in hypothalamus. The remarkably selective patterns of cellular retinol-binding protein type I- and cellular retinoic acid-binding protein type I-immunoreactivity discovered in the adult rat brain suggest that retinoids have important roles as regulators of gene expression in normal brain function. The high levels of cellular retinol-binding protein type I-immunoreactivity found in hippocampus suggest that one such role might relate to brain plasticity.

Constitutive Expression of Interleukin-1α Messenger Ribonucleic Acid in Rat Sertoli Cells Is Dependent upon Interaction with Germ Cells1

Interleukin-1 (IL-1), a proinflammatory cytokine originally isolated as a product of activated mononuclear phagocytes, consists of two distinct agonist proteins, IL-1α and IL-1β, of which IL-1β is the major inducible IL-1 protein produced by macrophages. We show here that mRNA of IL-1α, but not IL-1β, is constitutively expressed by the intact rat testis and localize the transcript to Sertoli cells as confirmed by a novel squash technique. The expression is developmentally regulated and appears only after postnatal day 20 in the rat testis, corresponding to onset of puberty. IL-1α mRNA shows a stage-dependent expression pattern during the cycle of the seminiferous epithelium. It is low or absent in stage VII, but present in all other stages of the cycle. The same stage-dependent distribution was also observed at the protein level when bioactive IL-1 was measured in extracts of accurately defined one millimeter segments of seminiferous tubules. No IL-1α mRNA was detected in adult rat testes after germ cell ...

Tyrosinemia: An inborn error of tyrosine metabolism with cirrhosis of the liver and multiple renal tubular defects (de Toni-Debré-Fanconi syndrome)+

The clinical and biochemical features are recorded of 7 patients with multiple renal tubular defects similar to those of the de Toni-Debre-Fanconi syndrome, nodular cirrhosis of the liver, and impaired tyrosine metabolism. Biochemically, the condition is characterized by the urinary excretion of large amounts of tyrosine and tyrosyl compounds and by tyrosinemia. Among the abnormal substances excreted, p -hydroxyphenyllactic acid usually exceeded that of other compounds. The total excretion of Millon positive substances roughly corresponded to the dietary intake of phenylalanine and tyrosine. In liver biopsies p -hydroxyphenylpyruvate oxidase activity was completely lacking whereas tyrosine-α-ketoglutarate transaminase activity was the same as in livers of control subjects. The disease seems to be inherited as an autosomal recessive gene. The hypothesis that there is an inborn error of tyrosine metabolism with a complete block at the step between p -hydroxyphenylpyruvate and homogentisate is advanced.

BCG-vaccination, tuberculin allergy and tuberculosis in school children; a follow-up study from Stockholm's elementary schools, 1945-51, with special regard to social factors.

Newborn infants of diabetic mothers have been kept thirsting and fasting during the first 2 or 3 days of life, i.e. as long as they have had generalized edema. During this period of starvation there was no tendency to pathological hypoglycemia; the blood sugar levels found in these cases were higher than that of normal newborns.

DEVELOPMENT OF RENAL CONTROL OF SALT AND FLUID HOMEOSTASIS DURING THE FIRST YEAR OF LIFE

ABSTRACT: Aperia, A., Broberger, O., Thodenius, K. and Zetterstrom, R. (Department of Paediatrics, Karolinska Institutet, St Gorans Hospital for Children, Stockholm, Sweden). Development of renal control of salt and fluid homeostasis during the first year of life. Acta Paediatr Scand, 64:393, 1975.–This study describes the development of renal control of salt and water homeostasis. Twenty‐three infants aged 3 weeks to 13 months were studied with respect to glomerular filtration rate (GFR) using single injection technique, ability to excrete an oral salt load, ability to excrete water, and diluting capacity. GFR developed exponentially, salt excretion linearly, water excretion was unchanged and diluting capacity actually decreased. A hypothesis is presented for the theoretical basis of this functional development taking into account the interdependence of the functional parameters studied. This theory might well explain the high incidence of hypernatremic dehydration in infants.