Small Extracellular Vesicles Secreted by Nigrostriatal Astrocytes Rescue Cell Death and Preserve Mitochondrial Function in Parkinson's Disease.

Extracellular vesicles (EVs) are emerging as powerful players in cell-to-cell communication both in healthy and diseased brain. In Parkinson's disease (PD)-characterized by selective dopaminergic neuron death in ventral midbrain (VMB) and degeneration of their terminals in striatum (STR)-astrocytes exert dual harmful/protective functions, with mechanisms not fully elucidated. Here, this study shows that astrocytes from the VMB-, STR-, and VMB/STR-depleted brains release a population of small EVs  in a region-specific manner. Interestingly, VMB-astrocytes secreted the highest rate of EVs, which is further exclusively increased in response to CCL3, a chemokine that promotes robust dopaminergic neuroprotection in different PD models. The neuroprotective potential of nigrostriatal astrocyte-EVs is investigated in differentiated versus undifferentiated SH-SY5Y cells exposed to oxidative stress and mitochondrial toxicity. EVs from both VMB- and STR-astrocytes counteract H2 O2 -induced caspase-3 activation specifically in differentiated cells, with EVs from CCL3-treated astrocytes showing a higher protective effect. High resolution respirometry further reveals that nigrostriatal astrocyte-EVs rescue neuronal mitochondrial complex I function impaired by the neurotoxin MPP+ . Notably, only EVs from VMB-astrocyte fully restore ATP production, again specifically in differentiated SH-SY5Y. These results highlight a regional diversity in the nigrostriatal system for the secretion and activities of astrocyte-EVs, with neuroprotective implications for PD.

Humanin gene expression in fibroblast of Down syndrome subjects.

Down syndrome (DS) is characterized by trisomy of chromosome 21 and peculiar phenotype. Humanin (HN) is a mitochondrial short 24-residue polypeptide whit anti-apoptotic and neuroprotective effects. In this study we evaluated HN protein expression and HN mRNA levels in cultured fibroblasts from DS patients and normal controls. Our results obtained by immunocytochemistry, western-blot and qRT-PCR analysis show a significant HN up-regulation in DS patients. These results confirm previous studies and suggest a role for HN may in the DS phenotype.

Parkinson's disease, aging and adult neurogenesis: Wnt/ß-catenin signalling as the key to unlock the mystery of endogenous brain repair.

A common hallmark of age-dependent neurodegenerative diseases is an impairment of adult neurogenesis. Wingless-type mouse mammary tumor virus integration site (Wnt)/ß-catenin (WßC) signalling is a vital pathway for dopaminergic (DAergic) neurogenesis and an essential signalling system during embryonic development and aging, the most critical risk factor for Parkinson's disease (PD). To date, there is no known cause or cure for PD. Here we focus on the potential to reawaken the impaired neurogenic niches to rejuvenate and repair the aged PD brain. Specifically, we highlight WßC-signalling in the plasticity of the subventricular zone (SVZ), the largest germinal region in the mature brain innervated by nigrostriatal DAergic terminals, and the mesencephalic aqueduct-periventricular region (Aq-PVR) Wnt-sensitive niche, which is in proximity to the SNpc and harbors neural stem progenitor cells (NSCs) with DAergic potential. The hallmark of the WßC pathway is the cytosolic accumulation of ß-catenin, which enters the nucleus and associates with T cell factor/lymphoid enhancer binding factor (TCF/LEF) transcription factors, leading to the transcription of Wnt target genes. Here, we underscore the dynamic interplay between DAergic innervation and astroglial-derived factors regulating WßC-dependent transcription of key genes orchestrating NSC proliferation, survival, migration and differentiation. Aging, inflammation and oxidative stress synergize with neurotoxin exposure in "turning off" the WßC neurogenic switch via down-regulation of the nuclear factor erythroid-2-related factor 2/Wnt-regulated signalosome, a key player in the maintenance of antioxidant self-defense mechanisms and NSC homeostasis. Harnessing WßC-signalling in the aged PD brain can thus restore neurogenesis, rejuvenate the microenvironment, and promote neurorescue and regeneration.

Neural Stem Cell Grafts Promote Astroglia-Driven Neurorestoration in the Aged Parkinsonian Brain via Wnt/ß-Catenin Signaling.

During aging-one the most potent risk factors for Parkinson's disease (PD)-both astrocytes and microglia undergo functional changes that ultimately hamper homoeostasis, defense, and repair of substantia nigra pars compacta (SNpc) midbrain dopaminergic (mDA) neurons. We tested the possibility of rejuvenating the host microenvironment and boosting SNpc DA neuronal plasticity via the unilateral transplantation of syngeneic neural stem/progenitor cells (NSCs) in the SNpc of aged mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced experimental PD. Transplanted NSCs within the aged SNpc engrafted and migrated in large proportions to the tegmental aqueduct mDA niche, with 30% acquiring an astroglial phenotype. Both graft-derived exogenous (ex-Astro) and endogenous astrocytes (en-Astro) expressed Wnt1. Both ex-Astro and en-Astro were key triggers of Wnt/ß-catenin signaling in SNpc-mDA neurons and microglia, which was associated with mDA neurorescue and immunomodulation. At the aqueduct-ventral tegmental area level, NSC grafts recapitulated a genetic Wnt1-dependent mDA developmental program, inciting the acquisition of a mature Nurr1+ TH+ neuronal phenotype. Wnt/ß-catenin signaling antagonism abolished mDA neurorestoration and immune modulatory effects of NSC grafts. Our work implicates an unprecedented therapeutic potential for somatic NSC grafts in the restoration of mDA neuronal function in the aged Parkinsonian brain. Stem Cells 2018;36:1179-1197.

Uncovering novel actors in astrocyte-neuron crosstalk in Parkinson's disease: the Wnt/ß-catenin signaling cascade as the common final pathway for neuroprotection and self-repair.

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by progressive loss of dopaminergic (DAergic) neuronal cell bodies in the substantia nigra pars compacta and gliosis. The cause and mechanisms underlying the demise of nigrostriatal DAergic neurons are ill-defined, but interactions between genes and environmental factors are recognized to play a critical role in modulating the vulnerability to PD. Current evidence points to reactive glia as a pivotal factor in PD pathophysiology, playing both protective and destructive roles. Here, the contribution of reactive astrocytes and their ability to modulate DAergic neurodegeneration, neuroprotection and neurorepair in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rodent model of PD will be discussed in the light of novel emerging evidence implicating wingless-type mouse mammary tumor virus integration site (Wnt)/ß-catenin signaling as a strong candidate in MPTP-induced nigrostriatal DAergic plasticity. In this work, we highlight an intrinsic Wnt1/frizzled-1/ß-catenin tone that critically contributes to the survival and protection of adult midbrain DAergic neurons, with potential implications for drug design or drug action in PD. The dynamic interplay between astrocyte-derived factors and neurogenic signals in MPTP-induced nigrostriatal DAergic neurotoxicity and repair will be summarized, together with recent findings showing a critical role of glia-neural stem/progenitor cell (NPC) interactions aimed at overcoming neurodegeneration and inducing neurorestoration. Understanding the intrinsic plasticity of nigrostriatal DAergic neurons and deciphering the signals facilitating the crosstalk between astrocytes, microglia, DAergic neurons and NPCs may have major implications for the role of stem cell technology in PD, and for identifying potential therapeutic targets to induce endogenous neurorepair.

Hormones are key actors in gene x environment interactions programming the vulnerability to Parkinson's disease: glia as a common final pathway.

Alterations in developmental programming of neuroendocrine and immune system function may critically modulate vulnerability to various diseases. In particular, genetic factors, including gender, may interact with early life events such as exposure to hormones, endotoxins, or neurotoxins, thereby influencing disease predisposition and/or severity, but little is known about the role of the astroglial cell compartment and its mediators in this phenomenon. Indeed, in the context of innate inflammatory mechanisms, a dysfunction of the astroglial cell compartment is believed to contribute to the selective degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta in Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. Hence, in response to brain injury the roles of astrocytes and microglia are very dynamic and cell type-dependent, in that they may exert the known proinflammatory (harmful) effects, but in certain circumstances they can turn into highly protective cells and exert anti-inflammatory (beneficial) functions, thereby facilitating neuronal recovery and repair. Here, we summarize our work suggesting a chief role of hormonal programming of glial response to inflammation and oxidative stress in MPTP-induced loss of DA neuron functionality and demonstrate that endogenous glucocorticoids and the female hormone estrogen (E(2)) inhibit the aberrant neuroinflammatory cascade, protect astrocytes and microglia from programmed cell death, and stimulate recovery of DA neuron functionality, thereby triggering the repair process. The overall results highlight glia as a final common pathway directing neuroprotection versus neurodegeneration. Such recognition of endogenous glial protective pathways may provide a new insight and may contribute to the development of novel therapeutic treatment strategies for PD and possibly other neurodegenerative disorders.

Glucocorticoid receptor deficiency increases vulnerability of the nigrostriatal dopaminergic system: critical role of glial nitric oxide.

Glucocorticoids (GCs) exert via glucocorticoid receptors (GRs) potent anti-inflammatory and immunosuppressive effects. Emerging evidence indicates that an inflammatory process is involved in dopaminergic nigro-striatal neuronal loss in Parkinson's disease. We here report that the GR deficiency of transgenic (Tg) mice expressing GR antisense RNA from early embryonic life has a dramatic impact in "programming" the vulnerability of dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The GR deficiency of Tg mice exacerbates MPTP-induced toxicity to dopaminergic neurons, as revealed by both severe loss of tyrosine hydroxylase positive nigral neurons and sharp decreases in striatal levels of dopamine and its metabolites. In addition, the late increase in dopamine oxidative metabolism and ascorbic acid oxidative status in GR-deficient mice was far greater than in wild-type (Wt) mice. Inducible nitric oxide synthase (iNOS) was sharply increased in activated astrocytes, macrophages/microglia of GR-deficient as compared with Wt mice. Moreover, GR-deficient microglia produced three- to fourfold higher nitrite levels than Wt mice; these increases preceded the loss of dopaminergic function and were resistant to GR the inhibitory effect of GC, pointing to peroxynitrites as candidate neurotoxic effectors. The iNOS inhibitor N6-(1-iminoethyl)-L-lysine normalized vulnerability of Tg mice, thus establishing a novel link between genetic impairment of GR function and vulnerability to MPTP.

Exposure to a dysfunctional glucocorticoid receptor from early embryonic life programs the resistance to experimental autoimmune encephalomyelitis via nitric oxide-induced immunosuppression.

Glucocorticoid (GC) hormones play a central role in the bidirectional communication between the neuroendocrine and the immune systems and exert, via GC receptors (GR), potent immunosuppressive and anti-inflammatory effects. In this study, we report that GR deficiency of transgenic mice expressing GR antisense RNA from early embryonic life has a dramatic impact in programming the susceptibility to experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. GR deficiency renders mice resistant to myelin oligodendrocyte glycoprotein-induced EAE, and such mice do not develop clinical or histological signs of disease compared with EAE-susceptible wild-type mice. Resistance to EAE in GR-deficient mice is associated not with endogenous GC levels, but with a significant reduction in spleen and lymph node cell proliferation. The use of NO inhibitors in vitro indicates that NO is the candidate immunosuppressor molecule. GR-deficient mice develop 3- to 6-fold higher nitrite levels in the periphery and are resistant to NO inhibition by GCs. Specific inhibition of NO production in vivo by treatment with the inducible NO synthase inhibitor, L-N(6)-(1-iminoethyl)-lysine, suppressed circulating nitrites, increased myelin oligodendrocyte glycoprotein-specific cell proliferation, and rendered GR-deficient mice susceptible to EAE. Thus, life-long GR deficiency triggers inducible NO synthase induction and NO generation with consequent down-regulation of effector cell proliferation. These findings identify a novel link among GR, NO, and EAE susceptibility and highlight NO as critical signaling molecule in bidirectional communication between the hypothalamic-pituitary-adrenocortical axis and the immune system.