Laurent Lecanu

A neuronal microtubule-interacting agent, NAPVSIPQ, reduces tau pathology and enhances cognitive function in a mouse model of Alzheimer's disease.

Neurofibrillary tangles composed of aggregated, hyperphosphorylated tau in an abnormal conformation represent one of the major pathological hallmarks of Alzheimers disease (AD) and other tauopathies. However, recent data suggest that the pathogenic processes leading to cognitive impairment occur before the formation of classic tangles. In the earliest stages of tauopathy, tau detaches from microtubules and accumulates in the cytosol of the somatodendritic compartment of cells. Either as a cause or an effect, tau becomes hyperphosphorylated and aggregates into paired helical filaments that comprise the tangles. To assess whether an agent that modulates microtubule function can inhibit the pathogenic process and prevent cognitive deficits in a transgenic mouse model with AD-relevant tau pathology, we administered the neuronal tubulin-preferring agent, NAPVSIPQ (NAP). Three months of treatment with NAP at an early-to-moderate stage of tauopathy reduced the levels of hyperphosphorylated soluble and insoluble tau. A 6-month course of treatment improved cognitive function. Although nonspecific tubulin-interacting agents commonly used for cancer therapy are associated with adverse effects due to their anti-mitotic activity, no adverse effects were found after 6 months of exposure to NAP. Our results suggest that neuronal microtubule interacting agents such as NAP may be useful therapeutic agents for the treatment or prevention of tauopathies.

Modeling Alzheimer's disease with non-transgenic rat models.

Alzheimers disease (AD), for which there is no cure, is the most common form of dementia in the elderly. Despite tremendous efforts by the scientific community, the AD drug development pipeline remains extremely limited. Animal models of disease are a cornerstone of any drug development program and should be as relevant as possible to the disease, recapitulating the disease phenotype with high fidelity, to meaningfully contribute to the development of a successful therapeutic agent. Over the past two decades, transgenic models of AD based on the known genetic origins of familial AD have significantly contributed to our understanding of the molecular mechanisms involved in the onset and progression of the disease. These models were extensively used in AD drug development. The numerous reported failures of new treatments for AD in clinical trials indicate that the use of genetic models of AD may not represent the complete picture of AD in humans and that other types of animal models relevant to the sporadic form of the disease, which represents 95% of AD cases, should be developed. In this review, we will discuss the evolution of non-transgenic rat models of AD and how these models may open new avenues for drug development.

Aging differentially affects male and female neural stem cell neurogenic properties

Purpose Neural stem cell transplantation as a brain repair strategy is a very promising technology. However, despite many attempts, the clinical success remains very deceiving. Despite clear evidence that sexual dimorphism rules many aspects of human biology, the occurrence of a sex difference in neural stem cell biology is largely understudied. Herein, we propose to determine whether gender is a dimension that drives the fate of neural stem cells through aging. Should it occur, we believe that neural stem cell sexual dimorphism and its variation during aging should be taken into account to refine clinical approaches of brain repair strategies. Methods Neural stem cells were isolated from the subventricular zone of three- and 20-month-old male and female Long-Evans rats. Expression of the estrogen receptors, ERα and ERβ, progesterone receptor, androgen receptor, and glucocorticoid receptor was analyzed and quantified by Western blotting on undifferentiated neural stem cells. A second set of neural stem cells was treated with retinoic acid to trigger differentiation, and the expression of neuronal, astroglial, and oligodendroglial markers was determined using Western blotting. Conclusion We provided in vitro evidence that the fate of neural stem cells is affected by sex and aging. Indeed, young male neural stem cells mainly expressed markers of neuronal and oligodendroglial fate, whereas young female neural stem cells underwent differentiation towards an astroglial phenotype. Aging resulted in a lessened capacity to express neuron and astrocyte markers. Undifferentiated neural stem cells displayed sexual dimorphism in the expression of steroid receptors, in particular ERα and ERβ, and the expression level of several steroid receptors increased during aging. Such sexual dimorphism might explain, at least in part, the sex difference in neural fate we observed in young and old neural stem cells. These results suggest that sex and aging are two factors to be taken into consideration for future neural stem cell transplantation protocols in brain repair strategies.

Neural stem cell sex dimorphism in aromatase (CYP19) expression: a basis for differential neural fate

Purpose Neural stem cell (NSC) transplantation and pharmacologic activation of endogenous neurogenesis are two approaches that trigger a great deal of interest as brain repair strategies. However, the success rate of clinical attempts using stem cells to restore neurologic functions altered either after traumatic brain injury or as a consequence of neurodegenerative disease remains rather disappointing. This suggests that factors affecting the fate of grafted NSCs are largely understudied and remain to be characterized. We recently reported that aging differentially affects the neurogenic properties of male and female NSCs. Although the sex steroids androgens and estrogens participate in the regulation of neurogenesis, to our knowledge, research on how gender-based differences affect the capacity of NSCs to differentiate and condition their neural fate is lacking. In the present study, we explored further the role of cell sex as a determining factor of the neural fate followed by differentiating NSCs and its relationship with a potential differential expression of aromatase (CYP19), the testosterone-metabolizing enzyme. Results Using NSCs isolated from the subventricular zone of three-month-old male and female Long-Evans rats and maintained as neurospheres, we showed that differentiation triggered by retinoic acid resulted in a neural phenotype that depends on cell sex. Differentiated male NSCs mainly expressed markers of neuronal fate, including βIII-tubulin, microtubule associated protein 2, growth-associated protein 43, and doublecortin. In contrast, female NSCs essentially expressed the astrocyte marker glial fibrillary acidic protein. Quantification of the expression of aromatase showed a very low level of expression in undifferentiated female NSCs, whereas aromatase expression in male NSCs was 14-fold greater than the female level. Conclusion Our results confirm our previous data that the neural phenotype acquired by differentiating NSCs largely depends on cell sex, and that differential expression of aromatase in undifferentiated NSCs might contribute to this sex-based dimorphism. Although still preliminary, our discovery may have clinical application in the development of future brain repair strategies.

Control of hypercholesterolemia and atherosclerosis using the cholesterol recognition/interaction amino acid sequence of the translocator protein TSPO

The translocator protein (18-kDa) TSPO is an ubiquitous high affinity cholesterol-binding protein reported to be present in the endothelial and smooth muscle cells of the blood vessels; its expression dramatically increased in macrophages found in atherosclerotic plaques. A domain in the carboxy-terminus of TSPO was identified and characterized as the cholesterol recognition/interaction amino acid consensus (CRAC). The ability of the CRAC domain to bind to cholesterol led us to hypothesize that this peptide could be used as an hypocholesterolemic, with potential anti-atherogenic properties, agent. We report herein the therapeutic benefit that resulted for the administration of the VLNYYVWR human CRAC sequence to guinea pigs fed with a high cholesterol diet and ApoE knock-out B6.129P2-Apoetm1Unc/J mice. CRAC treatment (3 and 30mg/kg once daily for 6 weeks) resulted in reduced circulating cholesterol levels in guinea pigs fed with 2% high cholesterol diet and ApoE knock-out B6.129P2-Apoetm1Unc/J mice. In high cholesterol fed guinea pigs, CRAC treatment administered once daily induced an increase in circulating HDL, decreased total, free and LDL cholesterol, and removed atheroma deposits in the aorta in a dose-dependent manner. The treatment also prevented the high cholesterol diet-induced increase in serum creatine kinase, total and isoforms, markers of neurological, cardiac and muscular damage. No toxicity was observed. Taken together these results support a role of TSPO in lipid homeostasis and atherosclerosis and indicate that CRAC may constitute a novel and safe treatment of hypercholesterolemia and atherosclerosis.

A Lead Study on Oxidative Stress-Mediated Dehydroepiandrosterone Formation in Serum: The Biochemical Basis for a Diagnosis of Alzheimer's Disease

Alzheimers disease (AD) is a progressive, yet irreversible, neurodegenerative disease for which there are limited means for its ante-mortem diagnosis. We previously identified a brain- and cell-specific oxidative stress-mediated mechanism for dehydroepiandrosterone (DHEA) biosynthesis present in rat, bovine, and human brain, independent of the cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17) enzyme activity found in the periphery. This alternative pathway is induced by pro-oxidant agents, such as Fe2+ and amyloid-β peptide. Using brain tissue specimens from control and AD patients we subsequently provided evidence that DHEA is formed in the AD brain by the oxidative stress-mediated metabolism of an unidentified precursor, thus depleting the levels of the precursor present in the blood stream. Here, we tested for the presence of this DHEA precursor in human serum using a simple Fe2+-based reaction and determined the amounts of DHEA formed. A total of 86 subjects were included in this study: 19 male and 20 female AD patients; 18 male and 22 female age-matched controls; and 4 men and 3 women with mild cognitive impairment. Serum oxidation resulted in a dramatic increase of DHEA level in control patients, whereas only a moderate or no increase was observed in the AD patients. The DHEA variation after oxidation correlated with the patients cognitive and mental status. These results suggest that the comparison of DHEA levels in patient serum before and after oxidation could provide a useful tool to diagnose AD.

Identification of small-molecule inhibitors of the steroidogenic acute regulatory protein (STARD1) by structure-based design

A homology model of the steroidogenic acute regulatory protein (STAR)-related lipid transfer (START) domain of STARD1 was built, and the cholesterol binding site was identified. Structure-based design studies were performed to identify small molecule inhibitors of the START domain. The lead compounds were selected based on cAMP-induced, but not 22R-hydroxycholesterol-supported, inhibition of steroid synthesis by 50% at 10 μM. The results obtained by molecular docking & dynamics show a good correlation between bioactivity, docking scores and calculated binding energies of ligand-protein complexes. The best active compounds will be optimized further and used to develop potential drugs to control excessive steroid formation.

Age and sex differences in neural stem cell transplantation: a descriptive study in rats.

Purpose The purpose of this study was to determine whether neural stem cell (NSC) sexual dimorphism previously demonstrated in vitro translates in vivo in NSC transplantation experiments and constitutes a defining factor of the transplantation outcome. Methods NSCs isolated from the subventricular zone of 2-day-old or 20-month-old male and female rats were grown as neurospheres prior to being transplanted in the striatum of 2-day-old or 20-month-old male and female recipient animals. The outcome of the transplantation and the NSC differentiation status were analyzed 8 weeks later by assessing the expression of the markers doublecortin (DCX) for neuroblasts, glial fibrillary acidic protein (GFAP) for astrocytes, nestin for stem cells, and choline acetyltransferase (ChAT) for neuronal cholinergic phenotype by immunofluorescence. Results No NSCs were detected in the brain of rat pups 8 weeks after transplantation. However, the endogenous neurogenesis was dramatically increased in a sex-dependent manner. These data suggest that the transplanted NSCs may have triggered endogenous neurogenesis by the intermediate growth factors they may have produced or the production they may have induced. However, NSCs transplanted into the striatum of adult rats were detectable at week 8. NSC survival was dependent on the sex and age of the donor and the recipient. Some of the transplanted cells were found to express DCX, GFAP, and ChAT, supporting an ongoing differentiation process toward astroglial and neuronal cholinergic phenotypes. Conclusion The outcome of the NSC transplantation was highly dependent on the sex and age of the combination donor/recipient. Data generated from our work may allow us in the future to answer the question “What NSCs and for whom?” and consequently lead to the optimization of the grafting process and improvement of the clinical prognosis.