A Fine Regulation of the Hippocampal Thyroid Signalling Protects Hypothyroid Mice against Glial Cell Activation.

Adult-onset hypothyroidism is associated with learning and cognitive dysfunctions, which may be related to alterations in synaptic plasticity. Local reduced levels of thyroid hormones (THs) may impair glia morphology and activity, and promote the increase of pro-inflammatory cytokine levels mainly in the hippocampus. Given that neuroinflammation induces memory impairments, hypothyroidism-related glia dysfunction may participate in brain disorders. Thus, we investigated the mechanisms linking hypothyroidism and neuroinflammation, from a protective perspective. We induced hypothyroidism in adult C57BL/6J and wild-derived WSB/EiJ male mice by a seven-week propylthiouracil (PTU) treatment. We previously showed that WSB/EiJ mice were resistant to high-fat diet (HFD)-induced obesity, showing no neuroinflammatory response through adaptive abilities, unlike C57BL/6J. As PTU and HFD treatments are known to induce comparable inflammatory responses, we hypothesized that WSB/EiJ mice might also be protected against hypothyroidism-induced neuroinflammation. We showed that hypothyroid WSB/EiJ mice depicted no hippocampal neuroinflammatory response and were able to maintain their hippocampal thyroid signalling despite low circulatisng TH levels. In contrast, C57BL/6J mice exhibited disturbed hippocampal TH signalling, accompanied by neuroinflammation and memory impairment. Our results reinforce the preponderance of the hippocampal TH regulatory system over TH circulating levels in the hippocampal glial reactivity.

Contrasting Functions of Mitogen- and Stress-activated Protein Kinases 1 and 2 in Recognition Memory and In Vivo Hippocampal Synaptic Transmission.

The mitogen-activated protein kinases (MAPK) are major signaling components of intracellular pathways required for memory consolidation. Mitogen- and stress-activated protein kinases 1 and 2 (MSK1 and MSK2) mediate signal transduction downstream of MAPK. MSKs are activated by Extracellular-signal Regulated Kinase 1/2 (ERK1/2) and p38 MAPK. In turn, they can activate cyclic AMP-response-element-binding protein (CREB), thereby modulating the expression of immediate early genes crucial for the formation of long-term memories. While MSK1 has been previously implicated in certain forms of learning and memory, little is known concerning MSK2. Our goal was to explore the respective contribution of MSK1 and MSK2 in hippocampal synaptic transmission and plasticity and hippocampal-dependent recognition memory. In Msk1- and Msk2-knockout mice, we evaluated object and object-place recognition memory, basal synaptic transmission, paired-pulse facilitation (PPF) and inhibition (PPI), and the capacity to induce and sustain long-term potentiation (LTP) in vivo. We also assessed the level of two proteins downstream in the MAPK/ERK1/2 pathway crucial for long-term memory, CREB and the immediate early gene (IEG) Early growth response 1 (EGR1). Loss of Msk1, but not of Msk2, affected excitatory synaptic transmission at perforant path-to-dentate granule cell synapses, altered short-term presynaptic plasticity, impaired selectively long-term spatial recognition memory, and decreased basal levels of CREB and its activated form. LTP in vivo and LTP-induced CREB phosphorylation and EGR1 expression were unchanged after Msk1 or Msk2 deletion. Our findings demonstrate a dissimilar contribution of MSKs proteins in cognitive processes and suggest that Msk1 loss-of-function only has a deleterious impact on neuronal activity and hippocampal-dependent memory consolidation.

Thyroid Hormone Supplementation Restores Spatial Memory, Hippocampal Markers of Neuroinflammation, Plasticity-Related Signaling Molecules, and ß-Amyloid Peptide Load in Hypothyroid Rats.

Hypothyroidism is a condition that becomes more prevalent with age. Patients with untreated hypothyroidism have consistently reported symptoms of severe cognitive impairments. In patients suffering hypothyroidism, thyroid hormone supplementation offers the prospect to alleviate the cognitive consequences of hypothyroidism; however, the therapeutic value of TH supplementation remains at present uncertain and the link between cellular modifications associated with hypothyroidism and neurodegeneration remains to be elucidated. In the present study, we therefore evaluated the molecular and behavioral consequences of T3 hormone replacement in an animal model of hypothyroidism. We have previously reported that the antithyroid molecule propylthiouracil (PTU) given in the drinking water favors cerebral atrophy, brain neuroinflammation, Aß production, Tau hyperphosphorylation, and altered plasticity-related cell-signaling pathways in the hippocampus in association with hippocampal-dependent spatial memory deficits. In the present study, our aim was to explore, in this model, the effect of hippocampal T3 signaling normalization on various molecular mechanisms involved in learning and memory that goes awry under conditions of hypothyroidism and to evaluate its potential for recovery of hippocampal-dependent memory deficits. We report that T3 supplementation can alleviate hippocampal-dependent memory impairments displayed by hypothyroid rats and normalize key markers of thyroid status in the hippocampus, of neuroinflammation, Aß production, and of cell-signaling pathways known to be involved in synaptic plasticity and memory function. Together, these findings suggest that normalization of hippocampal T3 signaling is sufficient to reverse molecular and cognitive dysfunctions associated with hypothyroidism.

PTU-induced hypothyroidism in rats leads to several early neuropathological signs of Alzheimer's disease in the hippocampus and spatial memory impairments.

The multifactorial causes impacting the risk of developing sporadic forms of Alzheimer's disease (AD) remain to date poorly understood. Epidemiologic studies in humans and research in rodents have suggested that hypothyroidism could participate in the etiology of AD. Recently, we reported that adult-onset hypothyroidism in rats favors ß-amyloid peptide production in the hippocampus. Here, using the same hypothyroidism model with the antithyroid molecule propythiouracyl (PTU), we further explored AD-related features, dysfunctional cell-signaling mechanisms and hippocampal-dependent learning and memory. In vivo MRI revealed a progressive decrease in cerebral volume of PTU-treated rats. In the hippocampus, hypothyroidism resulted in tau hyperphosphorylation and increases in several proinflammatory cytokines. These modifications were associated with impaired spatial memory and reduced hippocampal expression of signaling molecules important for synaptic plasticity and memory, including neurogranin, CaMKII, ERK, GSK3ß, CREB, and expression of the transcription factor EGR1/Zif268. These data strengthen the idea that hypothyroidism represents an important factor influencing the risk of developing sporadic forms of AD.

Methylaminolaevulinic acid photodynamic therapy in the treatment of erythroplasia of Queyrat.

BACKGROUND: Erythroplasia of Queyrat (EQ) is an intra-epithelial carcinoma of the penis. Progression to invasive carcinoma may occur. Its cause is unknown but some evidence suggests infection with human papillomavirus in the pathogenesis of EQ; however, recent data do not confirm this. Therapy is difficult and associated with important recurrence rates. Photodynamic therapy (PDT) employs a photosensitizer excited by visible light. The resulting photodynamic reaction selectively destroys atypical cells. Only few reports exist on the use of topical PDT in the treatment of EQ. OBJECTIVE: We report 11 cases of EQ treated by topical methylaminolaevulinic acid (MAL) PDT. RESULTS: Out of 11 male patients with EQ treated by topical MAL-PDT, 3 achieved complete remission sustained for 24 and 51 months and 4 a partial remission sustained for 2-45 months with a follow-up period of 4-45 months (1 patient lost to follow-up); surprisingly, 2 of the 4 patients with partial remission presented a complete remission after 20 and 45 months of follow-up, respectively, without further therapy. Four patients showed progression of the disease. CONCLUSION: Whereas topical MAL-PDT offers the advantages of tumour specificity, preservation of function and a good cosmetic result, side effects may cause treatment discontinuation in some cases. Treatment of EQ with PDT may represent a valuable option in selected cases, but our data do not allow considering it as a first-line therapeutic option.

Mitogen-activated protein/extracellular signal-regulated kinase kinase inhibition results in biphasic alteration of epidermal homeostasis with keratinocytic apoptosis and pigmentation disorders.

PURPOSE: Raf/mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK signaling pathway is constitutively activated in melanoma. AZD6244 blocks MEK1/2, inhibiting ERK phosphorylation. We focus on associated cutaneous toxicity and we attempt to understand the underlying pathophysiology and design treatment strategies. EXPERIMENTAL DESIGN: Dermatologic conditions of 22 patients with unresectable melanoma stage III/IV in a phase II trial were evaluated. Thirteen patients received AZD6244 initially, and nine patients were treated with AZD6244 following tumor progression with temozolomide. Biopsies were compared with matched controls in normal skin. Immunohistochemistry was performed. Half-side treatment of acute skin toxicity compared therapeutic options. RESULTS: Nineteen of 22 (86%) AZD6244-treated patients presented with cutaneous eruptions. Seventeen patients (77%) developed acute papulopustular rash. Chronic skin changes included xerosis, paronychia, and fissured fingertips, resembling cutaneous toxicity of epidermal growth factor receptor inhibition. In addition, we observed reduced pigmentation of hair and skin. Histology of acute skin lesions revealed a significant increase of apoptotic keratinocytes (P = 0.0008), focal neutrophilic infiltrates, destruction of the adnexal structures by neutrophils, and reduced cytokeratins. A significant proliferation shift from basal to suprabasal keratinocytes was shown in acute and chronic lesions. The number and viability of melanocytes was not affected. Corticosteroids plus antibacterial topical therapy ameliorate acute skin toxicity. CONCLUSIONS: AZD6244-associated skin reactions partly overlap with those observed upon epidermal growth factor receptor inhibition. Additionally, pigmentation of skin and hair is affected. The interruption of the MEK signaling pathway results in an acute keratinocyte stress response with disturbed epidermal homeostasis, inflammation, and tissue damage. Chronic adaptation controls inflammatory tissue damage but leads to cutaneous malfunctions that explain chronic skin toxicity.

T3 administration in adult hypothyroid mice modulates expression of proteins involved in striatal synaptic plasticity and improves motor behavior.

Adult-onset hypothyroidism is associated with neurological changes such as cognitive dysfunction and impaired learning, which may be related to alterations of synaptic plasticity. We investigate the consequence of adult-onset hypothyroidism on thyroid-mediated transcription events in striatal synaptic plasticity, and the effect of triiodothyronine (T3) replacement. We used hypothyroid mice, treated with propylthiouracil (PTU) and methimazole (MMI), with or without subsequent administration of T3. We evaluated the amount of T3 nuclear receptors (TRalpha1, TRbeta) and striatal plasticity indicators: neurogranin (RC3), Ras homolog enriched in striatum (Rhes), Ca2+/calmodulin-dependent protein kinase (CaMKII), and dopamine- and cAMP-regulated phosphoprotein (DARPP-32). In addition, we assessed hypothyroid mice motor behavior as related to striatum synaptic functions. Hypothyroid mice exhibited significantly reduced TRbeta, RC3 and Rhes expression. T3 administration reversed the expression of TRbeta, RC3, and up-regulated CaMKII levels as well as motor behavior, and decreased DARPP-32 protein phosphorylation. We suggest that thyroid hormone modulation had a major impact on striatal synaptic plasticity of adult mice which produced in turn motor behavior modifications.

Retinoic acid normalizes nuclear receptor mediated hypo-expression of proteins involved in beta-amyloid deposits in the cerebral cortex of vitamin A deprived rats.

Recent data have revealed that disruption of vitamin A signaling observed in Alzheimer's disease (AD) leads to a deposition of beta-amyloid (Abeta). The aim of this study was to precise the role of vitamin A and its nuclear receptors (RAR) in the processes leading to the Abeta deposits. Thus, the effect of vitamin A depletion and subsequent administration of retinoic acid (RA, the active metabolite of vitamin A) on the expression of RARbeta, and of proteins involved in amyloidogenic pathway, e.g., amyloid precursor protein (APP), beta-secretase enzyme (BACE), and APP carboxy-terminal fragment (APP-CTF) was examined in the whole brain, hippocampus, striatum, and cerebral cortex of rats. Rats fed a vitamin A-deprived diet for 13 weeks exhibited decreased amount of RARbeta, APP695, BACE, and of APP-CTF in the whole brain and in the cerebral cortex. Administration of RA is able to restore all expression. The results suggest that fine regulation of vitamin A mediated gene expression seems fundamental for the regulation of APP processing.

Age-related effects of ethanol consumption on triiodothyronine and retinoic acid nuclear receptors, neurogranin and neuromodulin expression levels in mouse brain.

The effects of ethanol consumption and ageing were investigated on the expression levels of retinoic acid (RA) and triiodothyronine (T3) nuclear receptors (RAR, RXR and TR) and of associated target genes involved in synaptic plasticity, neurogranin (RC3) and neuromodulin (GAP-43) in mice brain. For this purpose, C57BL/6 adult and aged mice were subjected to 5-month ethanol consumption and the mRNA expression of RAR, RXR, TR, RC3 and GAP-43 was measured using a real-time RT-PCR method. GAP-43 and RC3 protein levels also were measured by Western blot. Results showed that 12% ethanol consumption in adult mice (11 months) induced an increase in RARbeta, RXRbetagamma and TRalphabeta mRNA level in the brain with only an increase in RC3 expression. The same ethanol consumption in aged mice (22 months) reversed the age-related hypo-expression in brain RARbeta, TRalphabeta and target genes RC3 and GAP-43. Compared with our previous behavioral data showing that ethanol is able to partially suppress a selective age-related cognitive deficit, these results suggest that the ethanol-induced increase in RA and T3 nuclear receptors expression could be one of the mechanisms involved in the normalization of synaptic plasticity-associated gene expression altered in aging brain.

Vitamin A deficiency and relational memory deficit in adult mice: relationships with changes in brain retinoid signalling.

Vitamin A and its derivatives, the retinoids, have recently been reported to be implicated in the synaptic plasticity of the hippocampus and in cognitive functions. Acting via transcription factors, retinoids can regulate gene expression via their nuclear receptors [retinoic acid receptors (RARs) and retinoid X receptors (RXRs)]. We recently showed that a moderate (about 30%) hypoexpression of brain (and hippocampal) retinoid signalling, like that naturally occurring in the aged brain of mice, might be related to a selective relational memory deficit. To further assess this hypothesis, the present study investigated the effects of Vitamin A deprivation of varying duration both on the brain expression of retinoid receptors (RARbeta and RXRbeta/gamma) and two associated target genes [tissue-type transglutaminase (tTG) and neurogranin, (RC3)], and on radial maze discrimination learning using young adult mice as subjects. We observed that irrespective of its duration (i.e. 31 or 39 weeks), Vitamin A deprivation resulted in a significant reduction (25-30%) in the expression of brain RARbeta, RXRbeta/gamma and tTG mRNAs. Conversely, only the 39-week condition was found to induce a significant decrease in brain RC3 mRNAs contents and a selective relational memory impairment. Finally, daily administration of retinoic acid (RA) failed to reverse the 39-week Vitamin A deficiency (VAD)-related cognitive deficit and to fully normalise the associated brain retinoid hyposignalling. In particular, there was no evidence for an up-regulating effect of RA on whole brain (and hippocampal) RC3 mRNAs of the 39-week-depleted mice. The results show that post-natal VAD may induce a selective memory impairment and give further support to the hypothesis that the fine regulation of retinoid-mediated gene expression is important for optimal brain functioning and higher cognition.

Triiodothyronine administration reverses vitamin A deficiency-related hypo-expression of retinoic acid and triiodothyronine nuclear receptors and of neurogranin in rat brain.

Recent studies have revealed that retinoids play an important role in the adult central nervous system and cognitive functions. Previous investigations in mice have shown that vitamin A deficiency (VAD) generates a hypo-expression of retinoic acid (RA, the active metabolite of vitamin A) receptors and of neurogranin (RC3, a neuronal protein involved in synaptic plasticity) and a concomitant selective behavioural impairment. Knowing that RC3 is both a triiodothyronine (T3) and a RA target gene, and in consideration of the relationships between the signalling pathways of retinoids and thyroid hormones, the involvement of T3 on RA signalling functionality in VAD was investigated. Thus, the effects of vitamin A depletion and subsequent administration with RA and/or T3 on the expression of RA nuclear receptors (RAR, RXR), T3 nuclear receptor (TR) and on RC3 in the brain were examined. Rats fed a vitamin A-deficient diet for 10 weeks exhibited a decreased expression of RAR, RXR and TR mRNA and of RC3 mRNA and proteins. RA administration to these vitamin A-deficient rats reversed only the RA hypo-signalling in the brain. Interestingly, T3 is able to restore its own brain signalling simultaneously with that of vitamin A and the hypo-expression of RC3. These results obtained in vivo revealed that one of the consequences of VAD is a dysfunction in the thyroid signalling pathway in the brain. This seems of crucial importance since the down regulation of RC3 observed in the depleted rats was corrected only by T3.