With the aim to develop beneficial tracers for cerebral tumors, we tested two novel 5-iodo-2'-deoxyuridine (IUdR) derivatives, diesterified at the deoxyribose residue. The substances were designed to enhance the uptake into brain tumor tissue and to prolong the availability in the organism. We synthesized carrier added 5-[125I]iodo-3',5'-di-O-acetyl-2'-deoxyuridine (Ac2[125I]IUdR), 5-[125I]iodo-3',5'-di-O-pivaloyl-2'-deoxyuridine (Piv2[125I]IUdR) and their respective precursor molecules for the first time. HPLC was used for purification and to determine the specific activities. The iodonucleoside tracer were tested for their stability against human thymidine phosphorylase. DNA integration of each tracer was determined in 2 glioma cell lines (Gl261, CRL2397) and in PC12 cells in vitro. In mice, we measured the relative biodistribution and the tracer uptake in grafted brain tumors. Ac2[125I]IUdR, Piv2[125I]IUdR and [125I]IUdR (control) were prepared with labeling yields of 31-47% and radiochemical purities of >99% (HPLC). Both diesterified iodonucleoside tracers showed a nearly 100% resistance against degradation by thymidine phosphorylase. Ac2[125I]IUdR and Piv2[125I]IUdR were specifically integrated into the DNA of all tested tumor cell lines but to a less extend than the control [125I]IUdR. In mice, 24 h after i.p. injection, brain radioactivity uptakes were in the following order Piv2[125I]IUdR>Ac2[125I]IUdR>[125I]IUdR. For Ac2[125I]IUdR we detected lower amounts of radioactivities in the thyroid and stomach, suggesting a higher stability toward deiodination. In mice bearing unilateral graft-induced brain tumors, the uptake ratios of tumor-bearing to healthy hemisphere were 51, 68 and 6 for [125I]IUdR, Ac2[125I]IUdR and Piv2[125I]IUdR, respectively. Esterifications of both deoxyribosyl hydroxyl groups of the tumor tracer IUdR lead to advantageous properties regarding uptake into brain tumor tissue and metabolic stability.

A previous clinical trial studied the effect of long-term treatment with levodopa (LD) or the dopamine agonist pramipexole (PPX) on disease progression in Parkinson disease using SPECT with the dopamine transporter (DAT)-radioligand [(123)I]β-CIT as surrogate marker. [(123)I]β-CIT binding declined to significantly lower levels in patients receiving LD compared to PPX. However, the interpretation of this difference as LD-induced neurotoxicity, PPX-induced neuroprotection/-regeneration, or only drug-induced regulatory changes of DAT-availability remained controversial. To address this question experimentally, we induced a subtotal lesion of the substantia nigra in mice by bilateral injection of the neurotoxin 6-hydroxydopamine. After 4 weeks, mice were treated for 20 weeks orally with LD (100mg/kg/day) or PPX (3mg/kg/day), or water (vehicle) only. The integrity of nigrostriatal projections was assessed by repeated [(123)I]FP-CIT SPECT in vivo and by immunostaining for DAT and the dopamine-synthesizing enzyme tyrosine hydroxylase (TH) after sacrifice. In sham-lesioned mice, we found that both LD and PPX treatment significantly decreased the striatal FP-CIT binding (LD: -21%; PPX: -14%) and TH-immunoreactivity (LD: -42%; PPX: -45%), but increased DAT-immunoreactivity (LD: +42%; PPX: +33%) compared to controls without dopaminergic treatment. In 6-hydroxydopamine-lesioned mice, however, neither LD nor PPX significantly influenced the stably reduced FP-CIT SPECT signal (LD: -66%; PPX: -66%; controls -66%), TH-immunoreactivity (LD: -70%; PPX: -72%; controls: -77%) and DAT-immunoreactivity (LD: -70%; PPX: -75%; controls: -75%) in the striatum or the number of TH-positive cells in the substantia nigra (LD: -88%; PPX: -88%; controls: -86%), compared to lesioned mice without dopaminergic treatment. In conclusion, chronic dopaminergic stimulation with LD or PPX induced similar adaptive presynaptic changes in healthy mice, but no discernible changes in severely lesioned mice. These findings allow to more reliably interpret the results from clinical trials using neuroimaging of DAT as surrogate parameter.

Parkinson disease (PD) is characterized by dopaminergic neurodegeneration in the substantia nigra (SN). Recent evidence suggests that innate and adaptive immune responses can influence dopaminergic cell death in animal models of PD. However, the precise role of mononuclear phagocytes, key players in damaged tissue clearance and cross-talk with cells of adaptive immune system, remains open in PD. Mononuclear phagocytes in the brain occur as brain-resident microglia and as brain-infiltrating myeloid cells. To elucidate their differential contribution in the uptake of dopaminergic cell debris and antigen presentation capacity, we labeled nigral dopaminergic neurons retrogradely with inert rhodamine-conjugated latex retrobeads before inducing their degeneration by subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. We used green fluorescent protein (GFP)-expressing bone marrow chimeric mice to differentiate brain-infiltrating from brain-resident myeloid cells. We found that half of both endogenous (GFP-) and exogenous (GFP+) microglia (Iba1+) in the SN incorporated the tracer from degenerating dopaminergic neurons 1d after MPTP intoxication. In absolute numbers, endogenous microglia were much more activated to macrophages compared to exogenous myeloid cells at 1d after MPTP. Mainly the endogenous, tracer-phagocytosing microglia expressed the major histocompatibility complex (MHC) class II molecule for antigen presentation. Additionally, T-lymphocytes (Iba1-/GFP+/CD3+), which infiltrate the MPTP-lesioned SN, were mainly in direct contact with MHCII+ endogenous microglia. Our data suggest that brain-resident microglia are predominantly implicated in the removal of dopaminergic cell debris and the cross-talk with infiltrating T-lymphocytes in the SN in the MPTP mouse model of PD.

Parkinson's disease (PD) is a frequent neurodegenerative process in old age. Accumulation and aggregation of the lipid-binding SNARE complex component α-synuclein (SNCA) underlies this vulnerability and defines stages of disease progression. Determinants of SNCA levels and mechanisms of SNCA neurotoxicity have been intensely investigated. In view of the physiological roles of SNCA in blood to modulate vesicle release, we studied blood samples from a new large pedigree with SNCA gene duplication (PARK4 mutation) to identify effects of SNCA gain of function as potential disease biomarkers. Downregulation of complexin 1 (CPLX1) mRNA was correlated with genotype, but the expression of other Parkinson's disease genes was not. In global RNA-seq profiling of blood from presymptomatic PARK4 indviduals, bioinformatics detected significant upregulations for platelet activation, hemostasis, lipoproteins, endocytosis, lysosome, cytokine, Toll-like receptor signaling and extracellular pathways. In PARK4 platelets, stimulus-triggered degranulation was impaired. Strong SPP1, GZMH and PLTP mRNA upregulations were validated in PARK4. When analysing individuals with rapid eye movement sleep behavior disorder, the most specific known prodromal stage of general PD, only blood CPLX1 levels were altered. Validation experiments confirmed an inverse mutual regulation of SNCA and CPLX1 mRNA levels. In the 3'-UTR of the CPLX1 gene we identified a single nucleotide polymorphism that is significantly associated with PD risk. In summary, our data define CPLX1 as a PD risk factor and provide functional insights into the role and regulation of blood SNCA levels. The new blood biomarkers of PARK4 in this Turkish family might become useful for PD prediction.

The majority of investigations on HIV-associated neurocognitive disorders (HAND) neglect the cerebellum in spite of emerging evidence for its role in higher cognitive functions and dysfunctions in common neurodegenerative diseases.

Mechanisms behind how the immune system signals to the brain in response to systemic inflammation are not fully understood. Transgenic mice expressing Cre recombinase specifically in the hematopoietic lineage in a Cre reporter background display recombination and marker gene expression in Purkinje neurons. Here we show that reportergene expression in neurons is caused by intercellular transfer of functional Cre recombinase messenger RNA from immune cells into neurons in the absence of cell fusion. In vitro purified secreted extracellular vesicles (EVs) from blood cells contain Cre mRNA, which induces recombination in neurons when injected into the brain. Although Cre-mediated recombination events in the brain occur very rarely in healthy animals, their number increases considerably in different injury models, particularly under inflammatory conditions, and extend beyond Purkinje neurons to other neuronal populations in cortex, hippocampus, and substantia nigra. Recombined Purkinje neurons differ in their miRNA profile from their nonrecombined counterparts, indicating physiological significance. These observations reveal the existence of a previously unrecognized mechanism to communicate RNA-based signals between the hematopoietic system and various organs, including the brain, in response to inflammation.

Previously we demonstrated that systemically administered neuregulin-1-β1, a nerve growth and differentiation factor, passed the blood-brain barrier and accumulated in brain areas with expression of its receptor ErbB4. In substantia nigra (SN), neuregulin-1-β1 phosphorylated ErbB4 and protected dopaminergic neurons in a toxin-based mouse model of Parkinson disease (PD). We studied ErbB4 in the context of human midbrain dopaminergic degeneration in vivo and in vitro. Post-mortem ventral midbrain tissue sections of neuropsychiatric healthy individuals and PD patients (matched for age, gender and post-mortem delay) were immunostained for ErbB4. Cultured Lund human mesencephalic (LUHMES) post-mitotic dopaminergic neurons were treated with dopaminergic toxins and analyzed for ErbB4 expression. In control individuals, 85.0±5.0% of dopaminergic neurons, containing cytoplasmic neuromelanin, expressed ErbB4 in the SN. In PD cases, the percentage of ErbB4-positive nigral dopaminergic neurons was increased to 94.9±2.5%. The mean ErbB4 immunoreactivity of melanized neurons was higher in PD than controls. LUHMES neurons upregulated ErbB4 when exposed to toxins 1-methyl-4-phenylpyridinium and 6-hydroxydopamine. Increased rate of ErbB4-positive dopaminergic neurons in PD may either reflect a better survival of ErbB4-positive neurons or an increased expression of ErbB4 by remaining neurons to seek trophic support. Enhanced ErbB4 expression in human in vitro toxin-based PD models supports the latter interpretation. Thus, dopaminergic neurons in SN might be susceptible to neuregulin-1 treatment in PD.

In mammalians, toll-like receptors (TLR) signal-transduction pathways induce the expression of a variety of immune-response genes, including inflammatory cytokines. It is therefore plausible to assume that TLRs are mediators in glial cells triggering the release of cytokines that ultimately kill DA neurons in the substantia nigra in Parkinson disease (PD). Accordingly, recent data indicate that TLR4 is up-regulated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in a mouse model of PD. Here, we wished to evaluate the role of TLR4 in the acute mouse MPTP model of PD: TLR4-deficient mice and wild-type littermates control mice were used for the acute administration way of MPTP or a corresponding volume of saline. We demonstrate that TLR4-deficient mice are less vulnerable to MPTP intoxication than wild-type mice and display a decreased number of Iba1+ and MHC II+ activated microglial cells after MPTP application, suggesting that the TLR4 pathway is involved in experimental PD.