Association Between Diabetes Medications and the Risk of Parkinson's Disease: A Systematic Review and Meta-Analysis.

Background: Diabetes mellitus (DM) increases the risk of Parkinson's disease (PD). However, whether DM medications play a part on that increased PD risk is unclear. We designed this meta-analysis to assess the influence of different oral DM medications on the PD risk in patients with DM. Methods: We searched PubMed, Embase, and CENTRAL databases for relevant studies up until January 2021. We pooled adjusted outcomes to assess the PD risk in patients using different DM medications including sulfonylurea, metformin, glitazones (GTZ), dipeptidyl peptidase-4 inhibitors (DPP4i), and glucagon-like peptide-1 agonists (GLP1a). Results: We included 10 studies in our analysis. Our results indicate a lack of significant association between the PD risk and the use of sulfonylureas (three studies; HR, 1.26; 95% CI, 0.95 to 1.66; I 2, 70%; p = 0.11), DPP4i (three studies; HR, 0.69; 95% CI, 0.35 to 1.38; I 2, 88%; p = 0.30), metformin (five studies; HR, 1.23; 95% CI, 0.98 to 1.78; I 2, 84%; p = 0.13), and GTZ (six studies; HR, 0.88; 95% CI, 0.66 to 1.16; I 2, 92%; p = 0.35). After exclusion of a single study in the GTZ analysis, our results indicate a significantly reduced PD risk with GTZ use (HR, 0.78; 95% CI, 0.65 to 0.93; I 2, 59%; p = 0.06). Similarly, after the exclusion of a single study, our results indicate a significantly increased PD risk with the use of metformin (HR, 1.50; 95% CI, 1.11 to 2.02; I 2, 80%; p = 0.008). We also found a significantly reduced PD risk with the use of GLP1a (two studies; HR, 0.41; 95% CI, 0.19 to 0.87; I 2, 0%; p = 0.02). Conclusion: The role of different DM medications on the PD risk remains unclear, and the quality of studies is low. While our analysis suggests a lack of association between the use of metformin, GTZ, DPP4i, and sulfonylureas and the PD risk, metformin (to a higher degree) and GTZ may still increase the risk. Limited data suggest a protective effect of GLP1a on the PD risk.

MicroRNA-185 activates PI3K/AKT signalling pathway to alleviate dopaminergic neuron damage via targeting IGF1 in Parkinson's disease.

OBJECTIVES: Studies have extensively explored the role of microRNAs (miRs) in Parkinson's disease (PD) and miR-185 is related to autophagy and apoptosis of dopaminergic neurons in PD. However, the role of miR-185 mediating insulin-like growth factor 1 (IGF1)/phosphatidylinositol-3-kinase/protein kinase B signalling pathway (PI3K/AKT) in PD still needs in-depth exploration. METHODS: Rat PD models were established by injection of 6-hydroxydopamine. PD rats were injected with miR-185 or insulin-like growth factor 1 (IGF1)-related sequences. Behaviour tests were performed, oxidative stress-related factors, tyrosine hydroxylase (TH)-, glial fibrillary acidic protein (GFAP)-, ionised calcium-binding adaptor molecule-1 (Iba-1)- and TUNEL-positive cells in the substantia nigra were determined. Levels of miR-185, IGF1 and phosphatidylinositol-3-kinase/protein kinase B (PI3K/AKT) signalling pathway-related factors were also detected. RESULTS: miR-185 level was reduced in rats with PD. Restoring miR-185 promoted behaviour functions, ameliorated pathological damages and oxidative stress, increased TH-positive dopaminergic neurons, decreased GFAP- and Iba-1-positive cells and restrained neuronal apoptosis in the substantia nigra in PD rats. miR-185 targeted IGF1 to activate PI3K/AKT signalling pathway. Up-regulation of IGF1 mitigated restored miR-185-mediated effects on PD rats. CONCLUSION: This study illustrates that miR-185 ameliorates dopaminergic neuron damage via targeting IGF1 and activating PI3K/AKT signalling pathway in PD, which renews the therapy for PD.

Soluble Epoxide Hydrolase Deficiency or Inhibition Attenuates MPTP-Induced Parkinsonism.

Soluble epoxide hydrolase (sEH) inhibition has been demonstrated to have beneficial effects on various diseases, such as hypertension, diabetes, and brain ischemia. However, whether sEH inhibition has therapeutic potential in Parkinson's disease is still unknown. In this paper, we found that sEH expression is increased in 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP)-treated mice, and sEH deficiency and inhibition significantly attenuated tyrosine hydroxylase (TH)-positive cell loss and improved rotarod performance. The substrate of sEH, 14,15-epoxyeicosatrienoic acid (14,15-EET), protected TH-positive cells and alleviated the rotarod performance deficits of wild-type mice but not sEH-knockout mice. Moreover, the 14,15-EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) abolished the neuronal protective effects of sEH deficiency. In primary cultured cortical neurons, MPP(+) induced significant Akt inactivation in neurons from sEH wild-type mice, and this effect was not observed in neurons from knockout mice. Our data indicate that sEH deficiency and inhibition increased 14,15-EET in MPTP-treated mice, which activated the Akt-mediated protection of TH-positive neurons and behavioral functioning. We also found that sEH deficiency attenuated TH-positive cell loss in a paraquat-induced mouse model of Parkinson's. Our data suggest that sEH inhibition might be a powerful tool to protect dopaminergic neurons in Parkinson's disease.

Peroxisome proliferator-activated receptor γ is inhibited by histone deacetylase 4 in cortical neurons under oxidative stress.

Peroxisome proliferator-activated receptor γ (PPARγ) serves an essential protective function in neurons. Although PPARγ activation is known to reduce brain tissue damage in distinct models of brain diseases, the regulation of PPARγ activity in neurons is unclear. Here, we report that histone deacetylase 4 (HDAC4) mediates PPARγ inhibition in cultured cortical neurons under oxidative stress. Our data indicate that HDAC4 physically interacts with PPARγ and represses PPARγ transcription activity in cultured cortical neurons. Upon H(2) O(2) treatment, HDAC4 translocates from the cytoplasm to the nucleus, where it inhibits PPARγ transcription. This inhibition rendered neurons more vulnerable to H(2) O(2) insult. In contrast, knockdown of HDAC4 by introduction of a specific microRNA abolishes the oxidative stress-induced repression of PPARγ in neurons and also reduces the number of dead neurons induced by H(2) O(2.) Furthermore, over-expression of PPARγ protects neurons from either HDAC4 over-expression- or H(2) O(2) -induced damage. These data suggest that HDAC4 works to repress PPARγ transcription and regulates neuronal death by inhibiting PPARγ pro-survival activity.

[Prokaryotic expression and purification of N-terminal and C-terminal fragments of histone deacetylase 4].

OBJECTIVE: To express and purify the fusion proteins of glutathione S-transferase (GST)-N-terminal of histone deacetylase4 (HDAC4-N') (1-1952 bp) and GST- C-terminal of HDAC4 (HDAC4-C') (1708-3255 bp) in E.coli. METHODS: The DNA fragments (HDAC4-N' and HDAC4-C') amplified by PCR were ligated into GST fusion vector (pGEX-6P-1) to construct the recombinant plasmids. After identification with restriction digestion and DNA sequencing, the recombinant plasmids were transformed into E.coli BL21 and induced by IPTG for their expression. After identification by SDS-PAGE and Western blotting, the target proteins were purified by glutathione sepharose 4B. RESULTS: The results of restriction digestion and DNA sequencing confirmed successful construction of the recombinant plasmids. The relative molecular masses of the fusion proteins were approximately 110500 and 93080 as shown by SDS-PAGE. Western blotting demonstrated that the fusion proteins could be recognized by the specific anti-HDAC4 antibody. CONCLUSION: We have successfully constructed the recombinant expression vectors of pGEX-6P-1/HDAC4-N' and pGEX-6P-1/HDAC4-C' and induced the expression of the fusion proteins, which may facilitate functional studies of HDAC4 with other proteins.