Martin Holzenberger

Regulatory T cells delay disease progression in Alzheimer-like pathology

Recent studies highlight the implication of innate and adaptive immunity in the pathophysiology of Alzheimers disease, and foster immunotherapy as a promising strategy for its treatment. Vaccines targeting amyloid-β peptide provided encouraging results in mouse models, but severe side effects attributed to T cell responses in the first clinical trial AN1792 underlined the need for better understanding adaptive immunity in Alzheimers disease. We previously showed that regulatory T cells critically control amyloid-β-specific CD4(+) T cell responses in both physiological and pathological settings. Here, we analysed the impact of regulatory T cells on spontaneous disease progression in a murine model of Alzheimers disease. Early transient depletion of regulatory T cells accelerated the onset of cognitive deficits in APPPS1 mice, without altering amyloid-β deposition. Earlier cognitive impairment correlated with reduced recruitment of microglia towards amyloid deposits and altered disease-related gene expression profile. Conversely, amplification of regulatory T cells through peripheral low-dose IL-2 treatment increased numbers of plaque-associated microglia, and restored cognitive functions in APPPS1 mice. These data suggest that regulatory T cells play a beneficial role in the pathophysiology of Alzheimers disease, by slowing disease progression and modulating microglial response to amyloid-β deposition. Our study highlights the therapeutic potential of repurposed IL-2 for innovative immunotherapy based on modulation of regulatory T cells in Alzheimers disease.

Knockout of Insulin-Like Growth Factor-1 Receptor Impairs Distal Lung Morphogenesis

Background Insulin-like growth factors (IGF-I and -II) are pleiotropic regulators of somatic growth and development in vertebrate species. Endocrine and paracrine effects of both hormones are mediated by a common IGF type 1 receptor (IGF-1R). Lethal respiratory failure in neonatal IGF-1R knockout mice suggested a particular role for this receptor in pulmonary development, and we therefore investigated the consequences of IGF-1R inactivation in lung tissue. Methods and Findings We first generated compound heterozygous mutant mice harboring a hypomorphic (Igf1rneo) and a null (Igf1r−) allele. These IGF-1Rneo/− mice express only 22% of normal IGF-1R levels and are viable. In adult IGF-1Rneo/− mice, we assessed lung morphology and respiratory physiology and found normal histomorphometric characteristics and normal breathing response to hypercapnia. We then generated homozygous IGF-1R knockout mutants (IGF-1R−/−) and analyzed their lung development during late gestation using histomorphometric and immunohistochemical methods. IGF-1R−/− embryos displayed severe lung hypoplasia and markedly underdeveloped diaphragms, leading to lethal neonatal respiratory distress. Importantly, IGF-1R−/− lungs from late gestation embryos were four times smaller than control lungs and showed markedly thickened intersaccular mesenchyme, indicating strongly delayed lung maturation. Cell proliferation and apoptosis were significantly increased in IGF-1R−/− lung tissue as compared with IGF-1R+/+ controls. Immunohistochemistry using pro-SP-C, NKX2-1, CD31 and vWF as markers revealed a delay in cell differentiation and arrest in the canalicular stage of prenatal respiratory organ development in IGF-1R−/− mutant mice. Conclusions/Significance We found that low levels of IGF-1R were sufficient to ensure normal lung development in mice. In contrast, complete absence of IGF-1R significantly delayed end-gestational lung maturation. Results indicate that IGF-1R plays essential roles in cell proliferation and timing of cell differentiation during fetal lung development.

IGF-IR determines the fates of BCR/ABL leukemia

BackgroundThe tyrosine kinase receptor insulin-like growth factor 1 receptor (IGF-IR) contributes to the initiation and progression of many types of malignancies. We previously showed that IGF-2, which binds IGF-IR, is an extrinsic factor that supports the ex vivo expansion of hematopoietic stem cells (HSCs). We also demonstrated that IGF-IR is not required for HSC activity in vivo.Methods and resultsHere we investigated the role of IGF-IR in chronic myeloid leukemia (CML) using the retroviral BCR/ABL transplantation mouse model. Existing antibodies against IGF-IR are not suitable for flow cytometry; therefore, we generated a fusion of the human IgG Fc fragment with mutant IGF-2 that can bind to IGF-IR. We used this fusion protein to evaluate mouse primary hematopoietic populations. Through transplantation assays with IGF-IR+ and IGF-IR− cells, we demonstrated that IGF-IR is expressed on all mouse HSCs. The expression of IGF-IR is much higher on CML cells than on acute lymphoblastic leukemia (ALL) cells. The depletion of IGF-IR expression in BCR/ABL+ cells led to the development of ALL (mostly T cell ALL) but not CML. Lack of IGF-IR resulted in decreased self-renewal of the BCR/ABL+ CML cells in the serial replating assay.ConclusionIGF-IR regulates the cell fate determination of BCR/ABL+ leukemia cells and supports the self-renewal of CML cells.

Expression of dominant-negative thyroid hormone receptor alpha1 in Leydig and Sertoli cells demonstrates no additional defect compared with expression in Sertoli cells only.

Background In the testis, thyroid hormone (T3) regulates the number of gametes produced through its action on Sertoli cell proliferation. However, the role of T3 in the regulation of steroidogenesis is still controversial. Methods The TRαAMI knock-in allele allows the generation of transgenic mice expressing a dominant-negative TRα1 (thyroid receptor α1) isoform restricted to specific target cells after Cre-loxP recombination. Here, we introduced this mutant allele in both Sertoli and Leydig cells using a novel aromatase-iCre (ARO-iCre) line that expresses Cre recombinase under control of the human Cyp19(IIa)/aromatase promoter. Findings We showed that loxP recombination induced by this ARO-iCre is restricted to male and female gonads, and is effective in Sertoli and Leydig cells, but not in germ cells. We compared this model with the previous introduction of TRαAMI specifically in Sertoli cells in order to investigate T3 regulation of steroidogenesis. We demonstrated that TRαAMI-ARO males exhibited increased testis weight, increased sperm reserve in adulthood correlated to an increased proliferative index at P3 in vivo, and a loss of T3-response in vitro. Nevertheless, TRαAMI-ARO males showed normal fertility. This phenotype is similar to TRαAMI-SC males. Importantly, plasma testosterone and luteinizing hormone levels, as well as mRNA levels of steroidogenesis enzymes StAR, Cyp11a1 and Cyp17a1 were not affected in TRαAMI-ARO. Conclusions/Significance We concluded that the presence of a mutant TRαAMI allele in both Leydig and Sertoli cells does not accentuate the phenotype in comparison with its presence in Sertoli cells only. This suggests that direct T3 regulation of steroidogenesis through TRα1 is moderate in Leydig cells, and that Sertoli cells are the main target of T3 action in the testis.

Insulin-like growth factor 1 receptor regulates hypothermia during calorie restriction

Significance Energy homeostasis is fundamental for the survival of living organisms and contributes to their health, longevity, and aging. When food resources are scarce, and during experimental calorie restriction, endothermic animals can lower their core body temperature. Here, we found that this response is regulated by the insulin-like growth factor 1 receptor. This demonstrates that the three main factors affecting aging and longevity (calorie restriction, reduction of the insulin-like growth factor 1 signaling, and lowered temperature) are components of the same pathway that modulates energy homeostasis. The finding also identifies body temperature reduction as a common determinant of the effects of both calorie restriction and reduced insulin-like growth factor 1 receptor signaling. When food resources are scarce, endothermic animals can lower core body temperature (Tb). This phenomenon is believed to be part of an adaptive mechanism that may have evolved to conserve energy until more food becomes available. Here, we found in the mouse that the insulin-like growth factor 1 receptor (IGF-1R) controls this response in the central nervous system. Pharmacological or genetic inhibition of IGF-1R enhanced the reduction of temperature and of energy expenditure during calorie restriction. Full blockade of IGF-1R affected female and male mice similarly. In contrast, genetic IGF-1R dosage was effective only in females, where it also induced transient and estrus-specific hypothermia in animals fed ad libitum. These effects were regulated in the brain, as only central, not peripheral, pharmacological activation of IGF-1R prevented hypothermia during calorie restriction. Targeted IGF-1R knockout selectively in forebrain neurons revealed that IGF signaling also modulates calorie restriction-dependent Tb regulation in regions rostral of the canonical hypothalamic nuclei involved in controlling body temperature. In aggregate, these data identify central IGF-1R as a mediator of the integration of nutrient and temperature homeostasis. They also show that calorie restriction, IGF-1R signaling, and body temperature, three of the main regulators of metabolism, aging, and longevity, are components of the same pathway.

Disrupting IGF Signaling in Adult Mice Conditions Leanness, Resilient Energy Metabolism, and High Growth Hormone Pulses

Growth hormone (GH) and insulinlike growth factor (IGF) promote aging and age-related pathologies. Inhibiting this pathway by targeting IGF receptor (IGF-1R) is a promising strategy to extend life span, alleviate age-related diseases, and reduce tumor growth. Although anti-IGF-1R agents are being developed, long-term effects of IGF-1R blockade remain unknown. In this study, we used ubiquitous inducible IGF-1R knockout (UBIKOR) to suppress signaling in all adult tissues and screened health extensively. Surprisingly, UBIKOR mice showed no overt defects and presented with rather inconspicuous health, including normal cognition. Endocrine GH and IGF-1 were strongly upregulated without causing acromegaly. UBIKOR mice were strikingly lean with coordinate changes in body composition and organ size. They were insulin resistant but preserved physiological energy expenditure and displayed enhanced fasting metabolic flexibility. Thus, long-term IGF-1R blockade generated beneficial effects on aging-relevant metabolism, but exposed to high GH. This needs to be considered when targeting IGF-1R to protect from neurodegeneration, retard aging, or fight cancer.

CaMKIIα Expression Defines Two Functionally Distinct Populations of Granule Cells Involved in Different Types of Odor Behavior

Granule cells (GCs) in the olfactory bulb (OB) play anxa0important role in odor information processing. Although they have been classified into various neurochemical subtypes, the functional roles of these subtypes remain unknown. We used inxa0vivo two-photon Ca2+ imaging combined with cell-type-specific identification of GCs in the mouse OB to examine whether functionally distinct GC subtypes exist in the bulbar network. We showed that half of GCs express Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα+) and that these neurons are preferentially activated by olfactory stimulation. The higher activity of CaMKIIα+ neurons is due to the weaker inhibitory input that they receive compared to their CaMKIIα-immunonegative (CaMKIIα-) counterparts. In line with these functional data, immunohistochemical analyses showed that 75%-90% of GCs expressing the immediate early gene cFos are CaMKIIα+ in naive animals and in mice that have been exposed to a novel odor and go/no-go operant conditioning, or that have been subjected to long-term associative memory and spontaneous habituation/dishabituation odor discrimination tasks. On the other hand, a perceptual learning task resulted in increased activation of CaMKIIα- cells. Pharmacogenetic inhibition of CaMKIIα+ GCs revealed that this subtype is involved in habituation/dishabituation and go/no-go odor discrimination, but not in perceptual learning. In contrast, pharmacogenetic inhibition of GCs in a subtype-independent manner affected perceptual learning. Our results indicate that functionally distinct populations of GCs exist in the OB and that they play distinct roles during different odor tasks.

Thyrocyte-specific deletion of insulin and IGF-1 receptors induces papillary thyroid carcinoma-like lesions through EGFR pathway activation: Insulin and IGF-1 receptors in thyroid cancer development

Insulin and insulin‐like growth factor (IGF)‐1 signaling in the thyroid are thought to be permissive for the coordinated regulation by thyroid‐stimulating hormone (TSH) of thyrocyte proliferation and hormone production. However, the integrated role of insulin receptor (IR) and IGF‐1 receptor (IGF‐1R) in thyroid development and function has not been explored. Here, we generated thyrocyte‐specific IR and IGF‐1R double knockout (DTIRKO) mice to precisely evaluate the coordinated functions of these receptors in the thyroid of neonates and adults. Neonatal DTIRKO mice displayed smaller thyroids, paralleling defective folliculogenesis associated with repression of the thyroid‐specific transcription factor Foxe1. By contrast, at postnatal day 14, absence of IR and IGF‐1R paradoxically induced thyrocyte proliferation, which was mediated by mTOR‐dependent signaling pathways. Furthermore, we found elevated production of TSH during the development of follicular hyperplasia at 8 weeks of age. By 50 weeks, all DTIRKO mice developed papillary thyroid carcinoma (PTC)‐like lesions that correlated with induction of the ErbB pathway. Taken together, these data define a critical role for IR and IGF‐1R in neonatal thyroid folliculogenesis. They also reveal an important reciprocal relationship between IR/IGF‐1R and TSH/ErbB signaling in the pathogenesis of thyroid follicular hyperplasia and, possibly, of papillary carcinoma.

Super-sizing teeth – from mice to elephants

sexual dimorphism and sex-limited plasticity. Building up on our molecular understanding from one species, we explored the origin of phenotypic plasticity as a trait, and its necessary components in 20 representative species of nymphalid butterflies across nymphalid phylogeny. Our results show that plasticity in eyespot size is an ancestral trait in butterflies. In addition, they suggest that critical molecular components are ancestral and have since been lost in few species, and modified in few other species, in response to their rearing environments, possibly adding to adaptive advantages in each individual species. Our work provides first detailed examination of how a classic example of adaptive phenotypic plasticity originated and evolved in response to recurring seasonal environments.

Igf1r signalling acts on the anagen-to-catagen transition in the hair cycle

Insulin‐like growth factor 1 (Igf1) is important for skin development and homoeostasis. However, overexpression and inactivation studies have produced variable findings regarding its role in hair follicle (HF) biology. Here, we studied a conditional and inducible knockout of the Igf1 receptor (Igf1r) in keratin 15‐expressing bulge cells. Deletion of Igf1r after the development of the skin appendages in K15‐Igf1rKO mice showed no abnormalities in epidermal homoeostasis. Numbers of bulge cells were lower in K15‐Igf1rKO mice than in controls, without consequences on wound healing, at least in young mice. K15‐Igf1rKO HFs entered anagen phase earlier than controls and showed a delay in the anagen/catagen switch. The expression of Bmp‐4 mRNA was inhibited in HFs from K15‐Igf1rKO. MED1 transcription was impaired in the epidermis of K15‐Igf1rKO mice. These findings suggest that Igf1r controls the hair cycle, partly through Bmp‐4 activation.