Inga Hansson

The pineal hormone melatonin exaggerates development of collagen-induced arthritis in mice

We have previously shown that constant darkness enhances autoimmunity to type II collagen (CII) and exaggerates development of collagen-induced arthritis (CIA) in DBA/1 mice. This effect was suggested to be mediated via the major hormone of the pineal gland, melatonin, since this hormone (1) is known to be strongly dependent on environmental lighting and (2) has been reported to affect the immune function. The present study was performed in order to clarify if melatonin could account for the previous observation that mice kept in darkness had a more pronounced development of CIA. First, DBA/1 mice kept in constant darkness were analysed for serum melatonin levels. An increase in background levels in comparison to mice kept in a normal dark/light cycle or in constant light was recorded. Then, different groups of mice (kept in constant light in order to minimize endogenous melatonin levels) were immunised with rat CII to induce arthritis and injected with melatonin. Melatonin injections were performed daily (1 mg/kg b.w.) in the afternoons (at 4 p.m.) for 10 days at two different periods: day 1-10 after collagen injection, or at the onset of the disease (day 30-39). Mice injected with melatonin at day 1-10 developed a more severe arthritis while those injected at onset did not differ significantly from the corresponding controls. Our results support the hypothesis that the pineal gland can exaggerate the development of CIA via a high release of melatonin, probably via enhancement of T-cell priming.

GFAP promoter driven transgenic expression of PDGFB in the mouse brain leads to glioblastoma in a Trp53 null background

Glioblastomas are the most common and malignant astrocytic brain tumors in human adults. The tumor suppressor gene TP53 is commonly mutated and/or lost in astrocytic brain tumors and the TP53 alterations are often found in combination with excessive growth factor signaling via PDGF/PDGFRα. Here, we have generated transgenic mice over‐expressing human PDGFB in brain, under control of the human GFAP promoter. These mice showed no phenotype, but on a Trp53 null background a majority of them developed brain tumors. This occurred at 2–6 months of age and tumors displayed human glioblastoma‐like features with integrated development of Pdgfrα+ tumor cells and Pdgfrβ+/Nestin+ vasculature. The transgene was expressed in subependymal astrocytic cells, in glia limitans, and in astrocytes throughout the brain substance, and subsequently, microscopic tumor lesions were initiated equally in all these areas. With tumor size, there was an increase in Nestin positivity and variability in lineage markers. These results indicate an unexpected plasticity of all astrocytic cells in the adult brain, not only of SVZ cells. The results also indicate a contribution of widely distributed Pdgfrα+ precursor cells in the tumorigenic process.

Hippocalcin protects against caspase-12-induced and age-dependent neuronal degeneration

Hippocalcin is a neuronal calcium binding protein, but its physiological function in brain is unknown. We show here that hippocampal neurons from hippocalcin-deficient mice are more vulnerable to degeneration, particularly using thapsigargin, elevating intracellular calcium. Caspase-12 was activated in neurons lacking hippocalcin, while calpain was unchanged. Neuronal viability was accompanied by endoplasmic reticulum (ER) stress and a change in the relative induction of the ER chaperone, BiP/GRP78. Neuronal apoptosis inhibitor protein (NAIP), known to interact with hippocalcin, was not altered, but hippocampal neurons from gene-deleted mice were more sensitive to excitotoxicity caused by kainic acid. In addition, an age-dependent increase in neurodegeneration occurred in the gene-deleted mice, showing that hippocalcin contributes to neuronal viability during aging.

Platelet-derived growth factor receptor-alpha in ventricular zone cells and in developing neurons.

Cells in the early neuroepithelium differentiate and give rise to all cells in the central nervous system (CNS). The ways from a multipotent CNS stem cell to specialized neurons and glia are not fully understood. Using immunohistochemistry we found that neuroepithelial cells express the platelet-derived growth factor receptor-alpha (PDGFR-alpha) in the neural plate at embryonic day 8.5 and onwards in the neural tube. The protein was polarized to ventricular endfeet. Furthermore, PDGFR-alpha expression was localized to cells undergoing early neuronal development. We also found PDGFR-alpha expression in developing granule cells in the postnatal cerebellum, in Purkinje cells in the adult cerebellum and on processes of developing dorsal root ganglion cells. Previous reports mainly describe PDGFR-alpha expression in oligodendrocyte precursors and glial cells. We believe, in line with a few previous reports, that the PDGFR-alpha in addition marks a pool of undifferentiated cells, which are able to differentiate into neurons.

Constant darkness enhances autoimmunity to type II collagen and exaggerates development of collagen-induced arthritis in DBA/1 mice

The humoral function of the pineal gland is known to be strongly dependent on environmental lighting. Melatonin, the best characterized of the photo-dependent pineal hormones, has been reported to affect immune responses in mice. It has been hypothesized that the development of some types of psychosomatic and autoimmune diseases could be due to a disturbed release of this hormone. The present investigation was performed in order to evaluate effects of constant darkness (physiological stimulation of pineal melatonin synthesis) and constant light (physiological suppression of pineal melatonin synthesis) on the course of an experimental autoimmune model, the type II collagen-induced arthritis (CIA) in DBA/1 female mice. Mice kept in darkness develop more severe arthritis than those kept in constant light or in a normal dark/light rhythm (12 h light/12 h dark). Levels of anti-type II collagen antibodies were higher in mice kept in darkness, and the spleens of these animals were enlarged. Since castration of female DBA/1 mice enhances the severity of CIA, and since melatonin is known to exert effects on gonadal function, the experiment was repeated using oophorectomized mice. The same difference in arthritis severity between darkness- and light-exposed mice was obtained in this second experiment. We conclude that the exacerbation of arthritis in darkness is due to a darkness-induced change in levels of critical neurohumoral compound(s), that via gonadal independent mechanisms affect the autoimmune response. The exaggerated severity and chronicity of arthritis may be due to higher levels of melatonin in these animals.

Pinealectomy ameliorates collagen II-induced arthritis in mice

To extend our previous findings that exposure to constant darkness (stimulation of endogenous melatonin release) as well as treatment with exogenous melatonin magnifies the severity of collagen‐induced arthritis in mice, we have examined the effects of melatonin cutback by removing the pineal gland. Two strains of mice, DBA/1 and NFR/N, were subjected to surgical pinealectomy. The melalonin levels in sera were reduced by approximately 70% by the pinealectomy compared with the corresponding sham‐operated controls. After 3–4 weeks of rest the mice were immunized with rat type II collagen to induce autoimmune arthritis, and the animals were kept in constant darkness during the experiments. In comparison with the controls, all groups of pinealectomized mice showed reduced severity of the arthritis by means of (i) a slower onset of the disease, (ii)a less severe course of the disease (reduced clinical scores), and (iii) reduced serum levels of anti‐collagen II antibodies. These effects were not significant in all experiments, but the trends were always the same. Thus, the present results strengthen the hypothesis that high physiological levels of melatonin (which can be induced by exposure to darkness) stimulate the immune system and cause exacerbation of autoimmune collagen II arthritis, while inhibition of melatonin release (pinealectomy or exposure to light) has a beneficial effect.

INCREASED LEVELS OF PROLACTIN DURING, BUT NOT AFTER, THE IMMUNISATION WITH RAT COLLAGEN II ENHANCES THE COURSE OF ARTHRITIS IN DBA/1 MICE

In addition to its well known effects on reproductive organs and lactation the pituitary hormone prolactin (PRL) also influences immune functions. The present investigation was performed in order to clarify the regulatory role of prolactin in autoimmune disease by using the collagen II arthritis model. Groups of virgin female DBA/1 mice were subjected to different short-term treatment protocols (5-10 days) with rat PRL and the drugs bromocriptine (inhibits prolactin secretion) and haloperidol (enhances prolactin secretion). Treatments were performed at different stages of disease development, and effects on clinical scores, anti-collagen II antibody titres as well as agalactosyl IgG levels were recorded. The effects of the treatment protocols on serum PRL levels were assessed by using a radioimmunoassay (RIA) system. Although the accumulated results of the present study indicate that PRL does not fulfil a major role in the regulation of collagen II arthritis, some interesting observations were made. High levels of PRL (PRL injections) made the arthritis worse only if treatment was performed during the induction stage of the disease. Bromocriptine treatment during the immunisation period did not significantly affect the course of arthritis, but treatment at later stages tended to cause exacerbation (significant at the onset period only). These results indicate that PRL has different effects during early and late stages of the development of collagen II-induced arthritis.