Haplotype analysis of the PARK 11 gene, GIGYF2, in sporadic Parkinson's disease

RNA-binding protein GIGYF2 orchestrates hepatic insulin resistance through STAU1/PTEN-mediated disruption of the PI3K/AKT signaling cascade

BACKGROUND

Obesity is well-established as a significant contributor to the development of insulin resistance (IR) and diabetes, partially due to elevated plasma saturated free fatty acids like palmitic acid (PA). Grb10-interacting GYF Protein 2 (GIGYF2), an RNA-binding protein, is widely expressed in various tissues including the liver, and has been implicated in diabetes-induced cognitive impairment. Whereas, its role in obesity-related IR remains uninvestigated.

METHODS

In this study, we employed palmitic acid (PA) exposure to establish an in vitro IR model in the human liver cancer cell line HepG2 with high-dose chronic PA treatment. The cells were stained with fluorescent dye 2-NBDG to evaluate cell glucose uptake. The mRNA expression levels of genes were determined by real-time qRT-PCR (RT-qPCR). Western blotting was employed to examine the protein expression levels. The RNA immunoprecipitation (RIP) was used to investigate the binding between protein and mRNA. Lentivirus-mediated gene knockdown and overexpression were employed for gene manipulation. In mice, an IR model induced by a high-fat diet (HFD) was established to validate the role and action mechanisms of GIGYF2 in the modulation of HFD-induced IR in vivo.

RESULTS

In hepatocytes, high levels of PA exposure strongly trigger the occurrence of hepatic IR evidenced by reduced glucose uptake and elevated extracellular glucose content, which is remarkably accompanied by up-regulation of GIGYF2. Silencing GIGYF2 ameliorated PA-induced IR and enhanced glucose uptake. Conversely, GIGYF2 overexpression promoted IR, PTEN upregulation, and AKT inactivation. Additionally, PA-induced hepatic IR caused a notable increase in STAU1, which was prevented by depleting GIGYF2. Notably, silencing STAU1 prevented GIGYF2-induced PTEN upregulation, PI3K/AKT pathway inactivation, and IR. STAU1 was found to stabilize PTEN mRNA by binding to its 3'UTR. In liver cells, tocopherol treatment inhibits GIGYF2 expression and mitigates PA-induced IR. In the in vivo mice model, GIGYF2 knockdown and tocopherol administration alleviate high-fat diet (HFD)-induced glucose intolerance and IR, along with the suppression of STAU1/PTEN and restoration of PI3K/AKT signaling.

CONCLUSIONS

Our study discloses that GIGYF2 mediates obesity-related IR by disrupting the PI3K/AKT signaling axis through the up-regulation of STAU1/PTEN. Targeting GIGYF2 may offer a potential strategy for treating obesity-related metabolic diseases, including type 2 diabetes.

Drosophila Gyf/GRB10 interacting GYF protein is an autophagy regulator that controls neuron and muscle homeostasis

Autophagy is an essential process for eliminating ubiquitinated protein aggregates and dysfunctional organelles. Defective autophagy is associated with various degenerative diseases such as Parkinson disease. Through a genetic screening in Drosophila, we identified CG11148, whose product is orthologous to GIGYF1 (GRB10-interacting GYF protein 1) and GIGYF2 in mammals, as a new autophagy regulator; we hereafter refer to this gene as Gyf. Silencing of Gyf completely suppressed the effect of Atg1-Atg13 activation in stimulating autophagic flux and inducing autophagic eye degeneration. Although Gyf silencing did not affect Atg1-induced Atg13 phosphorylation or Atg6-Pi3K59F (class III PtdIns3K)-dependent Fyve puncta formation, it inhibited formation of Atg13 puncta, suggesting that Gyf controls autophagy through regulating subcellular localization of the Atg1-Atg13 complex. Gyf silencing also inhibited Atg1-Atg13-induced formation of Atg9 puncta, which is accumulated upon active membrane trafficking into autophagosomes. Gyf-null mutants also exhibited substantial defects in developmental or starvation-induced accumulation of autophagosomes and autolysosomes in the larval fat body. Furthermore, heads and thoraxes from Gyf-null adults exhibited strongly reduced expression of autophagosome-associated Atg8a-II compared to wild-type (WT) tissues. The decrease in Atg8a-II was directly correlated with an increased accumulation of ubiquitinated proteins and dysfunctional mitochondria in neuron and muscle, which together led to severe locomotor defects and early mortality. These results suggest that Gyf-mediated autophagy regulation is important for maintaining neuromuscular homeostasis and preventing degenerative pathologies of the tissues. Since human mutations in the GIGYF2 locus were reported to be associated with a type of familial Parkinson disease, the homeostatic role of Gyf-family proteins is likely to be evolutionarily conserved.

Follow-up study of variants of the GIGYF2 gene in Chinese patients with Parkinson’s disease

The Grb10-interacting GYF protein-2 gene (GIGYF2) is a PARK11 gene that reportedly has a causal role in familial Parkinson’s disease (PD) among populations from Italy and France. However, no comprehensive study of the GIGYF2 gene has been conducted among PD patients from mainland China. In our previous study, the GIGYF2 gene was directly sequenced, and nine missense variants and 14 polymorphisms were identified. For these 14 polymorphisms, in the present study we performed a case–control analysis for 300 PD patients and 200 healthy controls from mainland China. The c.297T>C p.Ala99Ala polymorphism was associated with increased risk with respect to the pathogenesis of sporadic PD. In conclusion, within the Chinese population, the c.297T>C p.Ala99Ala polymorphism of the GIGYF2 gene may be associated with an increased risk of developing PD.

No evidence for pathogenic role of GIGYF2 mutation in Parkinson disease in Japanese patients

Grb10-Interacting GYF Protein-2 (GIGYF2) is a candidate gene for PARK11 locus. To date, seven different GIGYF2 missense mutations have been identified in patients with familial Parkinson disease (PD) of European descent. To clarify the pathogenic role of GIGYF2 in PD, we analyzed the frequency of GIGYF2 mutations in 389 Japanese patients with PD (including 93 patients with late-onset familial PD, 276 with sporadic PD, and 20 with a single heterozygous mutation in the PD-associated genes), and 336 Japanese normal controls, by direct sequencing and/or high-resolution melting analysis. None of the reported GIGYF2 mutations or digenic mutations were detected. Two novel non-synonymous variants were identified (p.Q1211delQ and p.H1023Q), however, we could not determine their roles in PD. In summary, we found no evidence for PD-associated roles of GIGYF2 mutations. Our data suggest that GIGYF2 is unlikely to play a major role in PD in Japanese patients, similar to other populations.

Anxiety disorders in Parkinson's disease: prevalence and risk factors

Anxiety disorders are common in Parkinson's disease (PD) patients, yet are poorly studied. We examined the prevalence of anxiety disorders in PD, investigated the association between anxiety, and presentation and progression of PD, and studied for the first time the contribution of putative risk factors for anxiety in PD. A case-series of 79 PD patients recruited from neurology out-patient clinics was examined for anxiety disorders using the DSM-IV criteria. The Unified Parkinson's Disease Rating Scale and the Hoehn and Yahr Staging of PD were employed to understand the relationship between anxiety disorders, and the clinical presentation and severity of PD. A validated survey assessed putative risk factors for anxiety in PD. Twenty-five percent of PD patients were diagnosed with anxiety. Panic disorder, generalised anxiety disorder and social phobia were prevalent anxiety disorders. Comorbid depression with anxiety was observed (14%). The severity but not the duration of PD was positively related to anxiety. PD patients with postural instability and gait dysfunction symptom clustering were more likely to experience anxiety than tremor-dominant patients. While levodopa dosage had no relationship to anxiety, experience of dyskinesias or on/off fluctuations increased the risk. Lateralisation of PD had no association with anxiety. Anxiety disorders decreased with age and young onset PD patients were more likely to experience anxiety than the late onset subjects. Anxiety adds to the complexity of PD, lowering patients' quality of life. Future research can be directed to identify reactive and organic nature of anxiety in PD.

From genes to proteins in mendelian Parkinson's disease: an overview

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. A progressive movement disorder typified by the production of bradykinesia, tremor, rigidity, and impairment of postural reflexes, PD is characterized by a depletion of dopamine in the striatum. For the last decade, several Mendelian forms of PD have been identified. Mutations in these genes potentially lead to autosomal dominant (alpha-synuclein and LRRK2), or autosomal recessive PD (Parkin, PINK1, DJ1, and ATP13A2). This article will spotlight these six distinct genes unambiguously associated with Mendelian PD and the function of their encoded proteins.

Mutational screening and zebrafish functional analysis of GIGYF2 as a Parkinson-disease gene

The Grb10-Interacting GYF Protein-2 (GIGYF2) gene has been proposed as the Parkinson-disease (PD) gene underlying the PARK11 locus. However, association of GIGYF2 with PD has been challenged and a functional validation of GIGYF2 mutations is lacking. In this frame, we performed a mutational screening of GIGYF2 in an Italian PD cohort. Exons containing known mutations were analyzed in 552 cases and 552 controls. Thereafter, a subset of 184 familial PD cases and controls were subjected to a full coding-exon screening. These analyses identified 8 missense variations in 9 individuals (4 cases, 5 controls). Furthermore, we developed a zebrafish model of gigyf2 deficiency. Abrogation of gigyf2 function in zebrafish embryos did not lead to a drastic cell loss in diencephalic dopaminergic (DA) neuron clusters, suggesting that gigyf2 is not required for DA neuron differentiation. Notably, gigyf2 functional abrogation did not increase diencephalic DA neurons susceptibility to the PD-inducing drug MPP+. These data, together with those recently reported by other groups, suggest that GIGYF2 is unlikely to be the PARK11 gene.

GIGYF2 gene disruption in mice results in neurodegeneration and altered insulin-like growth factor signaling

Grb10-Interacting GYF Protein 2 (GIGYF2) was initially identified through its interaction with Grb10, an adapter protein that binds activated IGF-I and insulin receptors. The GIGYF2 gene maps to human chromosome 2q37 within a region linked to familial Parkinson's disease (PARK11 locus), and association of GIGYF2 mutations with Parkinson's disease has been described in some but not other recent publications. This study investigated the consequences of Gigyf2 gene disruption in mice. Gigyf2 null mice undergo apparently normal embryonic development, but fail to feed and die within the first 2 post-natal days. Heterozygous Gigyf2(+/-) mice survive to adulthood with no evident metabolic or growth defects. At 12-15 months of age, the Gigyf2(+/-) mice begin to exhibit motor dysfunction manifested as decreased balance time on a rotating horizontal rod. This is associated with histopathological evidence of neurodegeneration and rare intracytoplasmic Lewy body-like inclusions in spinal anterior horn motor neurons. There are alpha-synuclein positive neuritic plaques in the brainstem and cerebellum, but no abnormalities in the substantia nigra. Primary cultured embryo fibroblasts from Gigyf2 null mice exhibit decreased IGF-I-stimulated IGF-I receptor tyrosine phosphorylation and augmented ERK1/2 phosphorylation. These data provide further evidence for an important role of GIGYF2 in age-related neurodegeneration and IGF pathway signaling.

Is GIGYF2 the defective gene at the PARK11 locus?

The number of genes and loci for Parkinson's disease was expanded during 2008. Among the most interesting findings of the year was the nomination of GIGYF2 as the gene that is defective at the PARK11 locus and is a potentially frequent cause of typical Parkinson's disease. However, the optimism generated by the initial report has quickly been tempered by results obtained in the first wave of follow-up studies.