Discovery of NAFLD-Improving Agents by Promoting the Degradation of Keap1.

Activating Nrf2 through inhibiting Keap1 has been proven to alleviate oxidative stress and related diseases, including nonalcoholic fatty liver disease (NAFLD). Traditional Keap1 inhibitors could not avoid the "off-target" effects, but using proteolysis targeting chimera (PROTAC) technology to induce Keap1 degradation might be an effective strategy to find potential NAFLD improving agents. Thus, several PROTACs were designed and synthesized by harnessing CDDO as the Keap1 ligand in this study. PROTAC I-d exhibited optimal Keap1 degradation activity, which could increase the Nrf2 level and alleviate oxidative stress in free fatty acid-induced AML12 cells and the liver of mice fed with a methionine-choline-deficient diet. Moreover, compared with CDDO, PROTAC I-d displayed significant advantages in inhibiting hepatic steatosis, steatohepatitis, and fibrosis in the in vivo and in vitro models of NAFLD. In addition, PROTAC I-d also showed lower in vivo toxicity than CDDO. All these results suggested that PROTAC I-d might be a potential improving agent for NAFLD.

Dopamine D2 receptor agonist Bromocriptine ameliorates Aß1-42-induced memory deficits and neuroinflammation in mice.

Alzheimer's Disease (AD) is the most common neurodegenerative disease, which lacks disease-modifying therapeutics so far. Studies have shown that the dysfunction of the dopaminergic system is related to a variety of pathophysiology of AD, and the expression of Dopamine D2 receptor (DRD2) in the brains of AD patients and animal models is significantly downregulated, suggesting that DRD2 may represent a therapeutic target for AD. However, the strategy of targeting DRD2 for AD treatment still lacks some key experimental evidences. Here we show that DRD2 agonist Bromocriptine improved Aß1-42 induced neuroinflammation, neuronal apoptosis, and memory deficits in mice. For animal study, the mice have injected intracerebroventricularly (i.c.v.) with Aß1-42(410 pmol/5 µl) to induced AD cognitive deficit model (Mazzola et al., 2003; van der Stelt et al., 2006). After 7 days, Bromocriptine (2.5 mg/kg, 5 mg/kg and 10 mg/kg) or normal saline was administered intragastrically once a day for 30 days. Behavioral tests about the Y maze and Morris water maze in mice were initiated on the twenty-fourth day of drug administration for 7 days. In vivo and in vitro mechanism research revealed that Bromocriptine, via activating DRD2, promoted the recruitment of PP2A and JNK by scaffold protein ß-arrestin 2, that repressed JNK-mediated transcription of proinflammatory cytokines and activation of NLRP3 inflammasome in microglia. Collectively, our findings suggest that Bromocriptine can ameliorate Aß1-42 induced neuroinflammation and memory deficits in mice through DRD2/ß-arrestin 2/PP2A/JNK signaling axis, which provides an experimental basis for the development of Bromocriptine as a drug for AD.

DRD1 agonist A-68930 improves mitochondrial dysfunction and cognitive deficits in a streptozotocin-induced mouse model.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder characterized by irreversible cognitive deficits and memory dysfunction. Dopamine is the most abundant catecholaminergic neurotransmitter in the brain which regulates motivation, reward, movement, and cognition. Recently, increasing evidences have shown that dopaminergic system is disturbed in AD conditions, and pharmacological interventions targeting dopamine D1 receptor (DRD1) exhibit certain therapeutic benefits in AD models. However, the underlying link between DRD1 and AD remains elusive. This study sought to test whether the selective DRD1 agonist A-68930 could improve streptozotocin (STZ)-induced cognitive impairment in mice. Here we found that A-68930 treatment through intraperitoneal injection efficiently alleviated STZ-induced cognitive deficits in mice. Moreover, our mechanism researches revealed that the DRD1 signaling induced by A-68930 significantly rescued STZ-induced mitochondrial biogenesis deficit, mitochondrial dysfunction, Aß overexpression, and tau phosphorylation in mice hippocampus and cortex and SH-SY5Y cells, which may be mediated through stimulating AMPK/PGC-1α pathway. This study indicates that DRD1 agonist A-68930 can improve STZ-induced cognitive deficits and mitochondrial dysfunction in vivo and in vitro, and DRD1 may represent an appropriate target candidate for AD drug development.

GPR40 receptor agonist TAK-875 improves cognitive deficits and reduces ß-amyloid production in APPswe/PS1dE9 mice.

RATIONALE: Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive dysfunction and memory impairment. G protein-coupled receptor 40 (GPR40) is expressed in brain in addition to periphery and is associated with cognitive function such as space orientation, memory, and learning. However, the effects and mechanisms of GPR40 agonist in improving the AD progression remain largely unknown. OBJECTIVES: The present study aimed to investigate the therapeutic effects and mechanisms of a potent and selective GPR40 agonist TAK-875 on the APPswe/PS1dE9 mice. RESULTS: The results showed that intracerebroventricular administration of TAK-875 significantly rescued cognitive deficits in APPswe/PS1dE9 mice, and these effects may be mediated by the regulation of phospholipase C/protein kinase C signaling pathway, which enhanced α-secretase ADAM10 activity, promoted amyloid precursor protein non-amyloidogenic processing pathway, and reduced ß-amyloid production. CONCLUSIONS: These results suggest that GPR40 may be a potential therapeutic target for AD, and GPR40 agonists may become promising AD drugs in the future.

Dopamine D1 receptor agonist A-68930 ameliorates Aß1-42-induced cognitive impairment and neuroinflammation in mice.

Alzheimer's disease (AD) is an irreversible neurodegenerative disease characterized by progressive cognitive dysfunction and memory impairment. Dopamine is an important catecholaminergic neurotransmitter that controls movement, reward, motivation, and cognition. Recently, dopamine receptors were reported to regulate immune system in both periphery and central nervous system. However, whether dopamine D1 receptor (DRD1) activation could improve neuroinflammation in AD conditions remains unknown. The present study aimed to investigate the therapeutic effects and underlying mechanisms of a potent and selective DRD1 agonist A-68930 on Aß1-42-induced mice. Here we showed that intraperitoneal injection of A-68930 significantly ameliorated Aß1-42-induced cognitive dysfunction in mice. Moreover, both in vivo and in vitro data showed that A-68930-induced DRD1 activation significantly inhibited NLRP3 inflammasome-dependent neuroinflammation induced by Aß1-42, and this effect may be mediated by the activation of AMPK/autophagy signaling pathway, which enhanced NLRP3 inflammasome degradation and thus decreased the secretion of IL-1ß and IL-18. The present study suggests that A-68930-induced DRD1 signaling efficiently alleviates Aß1-42-induced cognitive impairment and neuroinflammation in mice and BV2 cells, and DRD1 may become a promising therapeutic target for AD.

The modulatory role of dopamine receptors in brain neuroinflammation.

Neuroinflammation is a general pathological feature of central nervous system (CNS) diseases, primarily caused by activation of astrocytes and microglia, as well as the infiltration of peripheral immune cells. Inhibition of neuroinflammation is an important strategy in the treatment of brain disorders. Dopamine (DA) receptor, a significant G protein-coupled receptor (GPCR), is classified into two families: D1-like (D1 and D5) and D2-like (D2, D3 and D4) receptor families, according to their downstream signaling pathways. Traditionally, DA receptor forms a wide variety of psychological activities and motor functions, such as voluntary movement, working memory and learning. Recently, the role of DA receptor in neuroinflammation has been investigated widely, mainly focusing on nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome, renin-angiotensin system, αB-crystallin, as well as invading peripheral immune cells, including T cells, dendritic cells, macrophages and monocytes. This review briefly outlined the functions and signaling pathways of DA receptor subtypes as well as its role in inflammation-related glial cells, and subsequently summarized the mechanisms of DA receptors affecting neuroinflammation. Meaningfully, this article provided a theoretical basis for drug development targeting DA receptors in inflammation-related brain diseases.

The ameliorative effects and underlying mechanisms of dopamine D1-like receptor agonist SKF38393 on Aß1-42-induced cognitive impairment.

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by extracellular amyloid plaques and intracellular neurofibrillary tangles. It is the most common form of human cognitive decline and dementia. In this study, we aim to systematically investigate the ameliorative effects of dopamine D1-like receptor agonist SKF38393 on cognitive dysfunction and explore its underlying mechanisms. The Aß1-42 was injected intracerebroventricularly to establish cognitive disorder model. Then, a series of behavior tests were used. In order to further study the mechanisms, some relevant protein was assessed by ELISA method and Western blot. The results in behavior tests revealed that SKF38393 significantly ameliorated all the test indexes compared with the model mice. Then SKF38393 increased phosphorylation of cAMP response element binding protein (CREB) and expression of Bcl-2 in Western blot analyses. Furthermore, in ELISA assay, SKF38393 significantly increased the brain-derived neurotrophic factor (BDNF) levels and reduced the ß-site APP cleaving enzyme1 (BACE1) and Aß1-42 levels in hippocampus and cortex of mice. However, compared with SKF38393-H, all these results were significantly reversed by the dopamine D1 receptor antagonist SCH23390. These results indicated that SKF38393 could ameliorate Aß1-42-induced cognitive dysfunction in mice, which may be related to D1 receptor activation. It leads to the phosphorylation of CREB, which promote the expression of BDNF, Bcl-2 and decrease the expression of Aß1-42 of mice. Our findings suggest that dopamine D1-like receptor may be a potential target for the treatment of AD and its agonists may become a novel drug in the future.