Glial cell line-derived neurotrophic factor is crucial for long-term maintenance of the nigrostriatal system

Role of Liver Growth Factor (LGF) in Parkinson's Disease: Molecular Insights and Therapeutic Opportunities

Parkinson's disease is the most common neurodegenerative movement disorder with unclear etiology and only symptomatic treatment to date. Toward the development of novel disease-modifying agents, neurotrophic factors represent a reasonable and promising therapeutic approach. However, despite the robust preclinical evidence, clinical trials using glial-derived neurotrophic factor (GDNF) and neurturin have been unsuccessful. In this direction, the therapeutic potential of other trophic factors in PD and the elucidation of the underlying molecular mechanisms are of paramount importance. The liver growth factor (LGF) is an albumin-bilirubin complex acting as a hepatic mitogen, which also exerts regenerative effects on several extrahepatic tissues including the brain. Accumulating evidence suggests that intracerebral and peripheral administration of LGF can enhance the outgrowth of nigrostriatal dopaminergic axonal terminals; promote the survival, migration, and differentiation of neuronal stem cells; and partially protect against dopaminergic neuronal loss in the substantia nigra of PD animal models. In most studies, these effects are accompanied by improved motor behavior of the animals. Potential underlying mechanisms involve transient microglial activation, TNF-α upregulation, and activation of the extracellular signal-regulated kinases 1/2 (ERK1/2) and of the transcription factor cyclic AMP response-element binding protein (CREB), along with anti-inflammatory and antioxidant pathways. Herein, we summarize recent preclinical evidence on the potential role of LGF in PD pathogenesis, aiming to shed more light on the underlying molecular mechanisms and reveal novel therapeutic opportunities for this debilitating disease.

RET isoforms contribute differentially to invasive processes in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a therapeutically challenging disease with poor survival rates, owing to late diagnosis and early dissemination. These tumors frequently undergo perineural invasion, spreading along nerves regionally and to distant sites. The RET receptor tyrosine kinase is implicated in increased aggressiveness, local invasion, and metastasis in multiple cancers, including PDAC. RET mediates directional motility and invasion towards sources of its neurotrophic factor ligands, suggesting that it may enhance perineural invasion of tumor cells towards nerves. RET is expressed as two main isoforms, RET9 and RET51, which differ in their protein interactions and oncogenic potentials, however, the contributions of RET isoforms to neural invasion have not been investigated. In this study, we generated total RET and isoform-specific knockdown PDAC cell lines and assessed the contributions of RET isoforms to PDAC invasive spread. Our data show that RET activity induces cell polarization and actin remodeling through activation of CDC42 and RHOA GTPases to promote directional motility in PDAC cells. Further, we show that RET interacts with the adaptor protein TKS5 to induce invadopodia formation, enhance matrix degradation and promote tumor cell invasion through a SRC and GRB2-dependent mechanism. Finally, we show that RET51 is the predominant isoform contributing to these RET-mediated invasive processes in PDAC. Together, our work suggests that RET expression in pancreatic cancers may enhance tumor aggressiveness by promoting perineural invasion, and that RET expression may be a valuable marker of invasiveness, and a potential therapeutic target in the treatment of these cancers.

Effects of GDNF-Transfected Marrow Stromal Cells on Rats with Intracerebral Hemorrhage

OBJECTIVE

The present study aimed to investigate the effects of Mesenchymal stem cells/glial cell line derived neurotrophic factor (MSCs/GDNF) transplantation on nerve reconstruction in rats with intracerebral hemorrhage.

METHODS

GDNF transduction to MSCs was using adenovirus vector pAdEasy-1-pAdTrack-CMV prepared. Intracerebral hemorrhage (ICH) was induced by injection of collagenase and heparin into the caudate putamen. At the third day after a collagenase-induced ICH, adult male SD rats were randomly divided into saline group, MSCs group and MSCs/GDNF group. Immunofluorescence and RT-PCR were performed to detect the differentiation of MSCs or MSCs with an adenovirus vector encoding GDNF gene in vivo and in vitro.

RESULT

After 6 hours of induction, both MSCs and MSCs/GDNF expressed neuro or glial specific markers and synaptic-associated proteins (SYN, GAP-43, PSD-95); additionally, they secreted bioactive compounds (BDNF, NGF-β). MSCs/GDNF transplantation, compared to MSCs and saline solution injection, significantly improved neurological functions after ICH. The grafted MSCs or MSCs/GDNF survived in the striatum after 2 weeks of transplantation and expressed the neural cell-specific biomarkers NSE, MAP2, and GFAP.

CONCLUSION

These findings demonstrate that MSCs/GDNF transplantation contributes to improved neurological function in experimental ICH rats. The mechanisms are possibly due to neuronal replacement and enhanced neurotrophic factor secretion.

Encapsulation of primary dopaminergic neurons in a GDNF-loaded collagen hydrogel increases their survival, re-innervation and function after intra-striatal transplantation

Poor graft survival limits the use of primary dopaminergic neurons for neural repair in Parkinson’s disease. Injectable hydrogels have the potential to significantly improve the outcome of such reparative approaches by providing a physical matrix for cell encapsulation which can be further enriched with pro-survival factors. Therefore, this study sought to determine the survival and efficacy of primary dopaminergic grafts after intra-striatal delivery in a glial-derived neurotrophic factor (GDNF)-loaded collagen hydrogel in a rat model of Parkinson’s disease. After intra-striatal transplantation into the lesioned striatum, the GDNF-enriched collagen hydrogel significantly improved the survival of dopaminergic neurons in the graft (5-fold), increased their capacity for striatal re-innervation (3-fold), and enhanced their functional efficacy. Additional studies suggested that this was due to the hydrogel’s ability to retain GDNF in the microenvironment of the graft, and to protect the transplanted cells from the host immune response. In conclusion, the encapsulation of dopaminergic neurons in a GDNF-loaded hydrogel dramatically increased their survival and function, providing further evidence of the potential of biomaterials for neural transplantation and brain repair in neurodegenerative diseases such as Parkinson’s disease.

Contrasting effects of selective MAGL and FAAH inhibition on dopamine depletion and GDNF expression in a chronic MPTP mouse model of Parkinson's disease

The modulation of the brain endocannabinoid system has been identified as an option to treat neurodegenerative diseases including Parkinson's disease (PD). Especially the elevation of endocannabinoid levels by inhibition of hydrolytic degradation represents a valuable approach. To evaluate whether monoacylglycerol lipase (MAGL) or fatty acid amide hydrolase (FAAH) inhibition could be beneficial for PD, we examined in parallel the therapeutic potential of the highly selective MAGL inhibitor KML29 elevating 2-arachidonoylglyerol (2-AG) levels and the highly selective FAAH inhibitor PF-3845 elevating anandamide (AEA) levels in a chronic methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid (MPTP/probenecid) mouse model of PD. Chronic administration of KML29 (10 mg/kg) but not PF-3845 (10 mg/kg) attenuated striatal MPTP/probenecid-induced dopamine depletion. Furthermore, KML29 induced an increase in Gdnf but not Bdnf expression, whereas PF-3845 decreased the MPTP/probenecid-induced Cnr2 expression without any effects on neurotrophin expression. Investigation of treatment-naïve striatal mRNA levels revealed a high presence of Gdnf and Mgll in contrast to Bdnf and Faah. Treatment of primary mouse microglia with 2-AG increased Gdnf but not Bdnf expression, suggesting that microglia might mediate the observed KML29-induced increase in Gdnf. In summary, pharmacological MAGL but not FAAH inhibition in the chronic MPTP/probenecid model attenuated the MPTP/probenecid-induced effects on striatal dopamine levels which were accompanied by an increase in 2-AG levels.

The rat striatum responds to nigro-striatal degeneration via the increased expression of proteins associated with growth and regeneration of neuronal circuitry

BACKGROUND

Idiopathic Parkinson's disease is marked by degeneration of dopamine neurons projecting from the substantia nigra to the striatum. Although proteins expressed by the target striatum can positively affect the viability and growth of dopaminergic neurons, very little is known about the molecular response of the striatum as nigro-striatal denervation progresses. Here, iTRAQ labelling and MALDI TOF/TOF mass spectrometry have been used to quantitatively compare the striatal proteome of rats before, during, and after 6-OHDA induced dopamine denervation.

RESULTS

iTRAQ analysis revealed the differential expression of 50 proteins at 3 days, 26 proteins at 7 days, and 34 proteins at 14 days post-lesioning, compared to the unlesioned striatum. While the denervated striatum showed a reduced expression of proteins associated with the loss of dopaminergic input (e.g., TH and DARPP-32), there was an increased expression of proteins associated with regeneration and growth of neurites (e.g., GFAP). In particular, the expression of guanine deaminase (GDA, cypin) - a protein known to be involved in dendritic branching - was significantly increased in the striatum at 3, 7 and 14 days post-lesioning (a finding verified by immunohistochemistry).

CONCLUSIONS

Together, these findings provide evidence to suggest that the response of the normal mammalian striatum to nigro-striatal denervation includes the increased expression of proteins that may have the capacity to facilitate repair and growth of neuronal circuitry.

GDNF is important for striatal organization and maintenance of dopamine neurons grown in the presence of the striatum

Glial cell line-derived neurotrophic factor (GDNF) exerts neuroprotective and neurorestorative effects on neurons and GDNF plays a significant role in maintenance of the dopamine neurons utilizing grafting to create a nigrostriatal microcircuit of Gdnf knockout (Gdnf(-/-)) tissue. To further evaluate the role of GDNF on organization of the nigrostriatal system, single or double grafts of ventral mesencephalon (VM) and lateral ganglionic eminence (LGE) with mismatches in Gdnf genotypes were performed. The survival of single grafts was monitored utilizing magnetic resonance imaging (MRI) and cell survival and graft organization were evaluated with immunohistochemistry. The results revealed that the size of VM single grafts did not change over time independent of genotype, while the size of the LGE transplants was significantly reduced already at 2 weeks postgrafting when lacking GDNF. Lack of GDNF did not significantly affect the survival of tyrosine hydroxylase (TH)-positive neurons in single VM grafts. However, the survival of TH-positive neurons was significantly reduced in VM derived from Gdnf(+/+) when co-grafted with LGE from the Gdnf(-/-) tissue. In contrast, lack of GDNF in the VM portion of co-grafts had no effect on the survival of TH-positive neurons when co-grafted with LGE from Gdnf(+/+) mice. The TH-positive innervation of co-grafts was sparse when the striatal co-grafts were derived from the Gdnf(-/-) tissue while dense and patchy when innervating LGE producing GDNF. The TH-positive innervation overlapped with the organization of dopamine and cyclic AMP-regulated phosphoprotein-relative molecular mass 32,000 (DARPP-32)-positive neurons, that was disorganized in LGE lacking GDNF production. In conclusion, GDNF is important for a proper striatal organization and for survival of TH-positive neurons in the presence of the striatal tissue.

Nigral GFRα1 infusion in aged rats increases locomotor activity, nigral tyrosine hydroxylase, and dopamine content in synchronicity

Delivery of exogenous glial cell line-derived neurotrophic factor (GDNF) increases locomotor activity in rodent models of aging and Parkinson's disease in conjunction with increased dopamine (DA) tissue content in substantia nigra (SN). Striatal GDNF infusion also increases expression of GDNF's cognate receptor, GFRα1, and tyrosine hydroxylase (TH) ser31 phosphorylation in the SN of aged rats long after elevated GDNF is no longer detectable. In aging, expression of soluble GFRα1 in the SN decreases in association with decreased TH expression, TH ser31 phosphorylation, DA tissue content, and locomotor activity. Thus, we hypothesized that, in aged rats, replenishing soluble GFRα1 in SN could reverse these deficits and increase locomotor activity. We determined that the quantity of soluble GFRα1 in young adult rat SN is ~3.6 ng. To replenish age-related loss, which is ~30 %, we infused 1 ng soluble GFRα1 bilaterally into SN of aged male rats and observed increased locomotor activity compared to vehicle-infused rats up to 4 days following infusion, with maximal effects on day 3. Five days after infusion, however, neither locomotor activity nor nigrostriatal neurochemical measures were significantly different between groups. In a separate cohort of male rats, nigral, but not striatal, DA, TH, and TH ser31 phosphorylation were increased 3 days following unilateral infusion of 1 ng soluble GFRα1into SN. Therefore, in aged male rats, the transient increase in locomotor activity induced by replenishing age-related loss of soluble GFRα1is temporally matched with increased nigral dopaminergic function. Thus, expression of soluble GFRα1 in SN may be a key component in locomotor activity regulation through its influence over TH regulation and DA biosynthesis.

Targeted delivery of GDNF through the blood-brain barrier by MRI-guided focused ultrasound

Neurotrophic factors, such as glial cell line-derived neurotrophic factor (GDNF), are promising therapeutic agents for neurodegenerative diseases. However, the application of GDNF to treat these diseases effectively is limited because the blood–brain barrier (BBB) prevents the local delivery of macromolecular therapeutic agents from entering the central nervous system (CNS). Focused ultrasound combined with microbubbles (MBs) using appropriate parameters has been previously demonstrated to be able to open the BBB locally and noninvasively. This study investigated the targeted delivery of GDNF MBs through the BBB by magnetic resonance imaging (MRI)-guided focused ultrasound. Evans Blue extravasation and histological examination were used to determine the optimum focused ultrasound parameters. Enzyme-linked immunosorbent assay was performed to verify the effects of GDNF bound on MBs using a biotin–avidin bridging chemistry method to promote GDNF delivery into the brain. The results showed that GDNF can be delivered locally and noninvasively into the CNS through the BBB using MRI-guided focused ultrasound combined with MBs under optimum parameters. MBs that bind GDNF combined with MRI-guided focused ultrasound may be an effective way of delivering neurotrophic factors directly into the CNS. The method described herein provides a potential means of treating patients with CNS diseases.