• BMB Reports
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• 제56권2호
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• pp.84-89
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• 2023

The implications of nutrient starvation due to aging on the degeneration of the retinal pigment epithelium (RPE) is yet to be fully explored. We examined the involvement of AMPK activation in mitochondrial homeostasis and its relationship with the maintenance of a healthy mitochondrial population and epithelial characteristics of RPE cells under nutrient starvation. Nutrient starvation induced mitochondrial senescence, which led to the accumulation of reactive oxygen species (ROS) in RPE cells. As nutrient starvation persisted, RPE cells underwent pathological epithelial-mesenchymal transition (EMT) via the upregulation of TWIST1, a transcription regulator which is activated by ROS-induced NF-κB signaling. Enhanced activation of AMPK with metformin decelerated mitochondrial senescence and EMT progression through mitochondrial biogenesis, primed by activation of PGC1-α. Thus, by facilitating mitochondrial biogenesis, AMPK protects RPE cells from the loss of epithelial integrity due to the accumulation of ROS in senescent mitochondria under nutrient starvation.

• 생명과학회지
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• 제29권10호
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• pp.1152-1158
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• 2019

겹삼잎국화는 한국에서 복통, 위염에 민간요법으로 사용되는 약초로 알려져있다. 하지만, 겹삼잎국화를 민간요법으로 사용되고 있으나 이 약초에 대한 연구는 거의 수행되어지지 않았다. 본 연구에서는 겹삼잎국화의 의학적 효과를 증명하기 위해 항비만 관련 연구를 수행하였다. 70% 에탄올을 이용한 겹삼잎국화 추출물의 항 비만 효과에 대한 연구를 위해 3T3-L1 지방전구세포를 사용하였으며, 지방전구세포가 지방세포로 성숙하는 것을 방지하고 이에 관련된 단백질 인자의 발현을 확인하기 위해 Oil Red O 염색법과 웨스턴 블롯, PCR을 통한 mRNA 분석이 수행되었다. DM (인슐린 칵테일)을 처리하여 지방전구세포의 성숙을 유도한 후, 겹삼잎국화 에탄올 추출물을 처리한 결과, $100{\mu}g/ml$ 농도에서 지방세포 분화 억제 효과와 세포 내 트리글리세리드(TG)의 수준이 현저하게 감소한 것을 확인하였다. 또한, 지방전구세포의 성숙에 관여하는 여러가지 단백질 등의 인자 발현율 또한 확인하였다. 겹삼잎국화 에탄올 추출물로 인해 $PPAR{\gamma}$, $C/EBP{\alpha}$, LPL, FAS와 같은 지방 세포의 성숙을 유도하는 인자가 조절되었으며, Acetyl-CoA carboxylase, AMP-activated protein kinase (AMPK) 등과 같은 단백질의 발현도 억제하여 분자적 기전 또한 규명하였다. 결론적으로, 겹삼잎국화 에탄올 추출물은 지방전구세포의 활성에 영향을 끼치지 않으며 지방세포로의 성숙을 유도하는 인자 및 단백질의 발현을 선택적으로 조절하여 항 비만 효과를 갖는 것으로 확인되었다.

• 생명과학회지
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• 제20권11호
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• pp.1617-1624
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• 2010

$\alpha$-MSH는 세포내 cAMP를 증폭시켜 멜라닌세포의 증식과 색소 증가에 관여한다. 본 연구에서는 $\alpha$-MSH로 자극한 B16F10 세포에서 세신추출물의 hypopigmenting 효과를 조사하고 그 억제기전에 대하여 조사하였다. 세신추출물은 $\alpha$-MSH에 의해 유도된 tyrosinase 활성과 멜라닌생성을 효과적으로 억제시켰으며, 이는 tyrosinase 발현을 조절하는 전사인자인 MITF의 발현억제와 연관성이 있었다. 즉 세신추출물은 MEK/ERK와 PI3K/Akt의 활성화를 통하여 MITF를 조절함으로서 $\alpha$-MSH에 의해 유도되는 tyrosinase, TRP-1, Dct 등 멜라닌생성관련 단백질을 억제함으로서 멜라닌생성을 저해하는 것으로 사료된다.

• Biomolecules & Therapeutics
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• 제29권6호
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• pp.615-629
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• 2021

An active compound, triterpene saponin, astersaponin I (AKNS-2) was isolated from Aster koraiensis Nakai (AKNS) and the autophagy activation and neuroprotective effect was investigated on in vitro and in vivo Parkinson's disease (PD) models. The autophagy-regulating effect of AKNS-2 was monitored by analyzing the expression of autophagy-related protein markers in SH-SY5Y cells using Western blot and fluorescent protein quenching assays. The neuroprotection of AKNS-2 was tested by using a 1-methyl-4-phenyl-2,3-dihydropyridium ion (MPP⁺)-induced in vitro PD model in SH-SY5Y cells and an MPTP-induced in vivo PD model in mice. The compound-treated SH-SY5Y cells not only showed enhanced microtubule-associated protein 1A/1B-light chain 3-II (LC3-II) and decreased sequestosome 1 (p62) expression but also showed increased phosphorylated extracellular signal-regulated kinases (p-Erk), phosphorylated AMP-activated protein kinase (p-AMPK) and phosphorylated unc-51-like kinase (p-ULK) and decreased phosphorylated mammalian target of rapamycin (p-mTOR) expression. AKNS-2-activated autophagy could be inhibited by the Erk inhibitor U0126 and by AMPK siRNA. In the MPP⁺-induced in vitro PD model, AKNS-2 reversed the reduced cell viability and tyrosine hydroxylase (TH) levels and reduced the induced α-synuclein level. In an MPTP-induced in vivo PD model, AKNS-2 improved mice behavioral performance, and it restored dopamine synthesis and TH and α-synuclein expression in mouse brain tissues. Consistently, AKNS-2 also modulated the expressions of autophagy related markers in mouse brain tissue. Thus, AKNS-2 upregulates autophagy by activating the Erk/mTOR and AMPK/mTOR pathways. AKNS-2 exerts its neuroprotective effect through autophagy activation and may serve as a potential candidate for PD therapy.

• The Korean Journal of Physiology and Pharmacology
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• 제19권6호
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• pp.507-514
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• 2015

Nitric oxide (NO) is important in the regulation of bone remodeling, whereas high concentration of NO promotes cell death of osteoblast. However, it is not clear yet whether NO-induced autophagy is implicated in cell death or survival of osteoblast. The present study is aimed to examine the role of NO-induced autophagy in the MC3T3-E1 cells and their underlying molecular mechanism. The effect of sodium nitroprusside (SNP), an NO donor, on the cytotoxicity of the MC3T3-E1 cells was determined by MTT assay and expression of apoptosis or autophagy associated molecules was evaluated by western blot analysis. The morphological observation of autophagy and apoptosis by acridine orange stain and TUNEL assay were performed, respectively. Treatment of SNP decreased the cell viability of the MC3T3-E1 cells in dose- and time-dependent manner. SNP increased expression levels of p62, ATG7, Beclin-1 and LC3-II, as typical autophagic markers and augmented acidic autophagolysosomal vacuoles, detected by acridine orange staining. However, pretreatment with 3-methyladenine (3MA), the specific inhibitor for autophagy, decreased cell viability, whereas increased the cleavage of PARP and caspase-3 in the SNP-treated MC3T3-E1 cells. AMP-activated protein kinase (AMPK), a major autophagy regulatory kinase, was activated in SNP-treated MC3T3-E1 cells. In addition, pretreatment with compound C, an inhibitor of AMPK, decreased cell viability, whereas increased the number of apoptotic cells, cleaved PARP and caspase-3 levels compared to those of SNP-treated MC3T3-E1 cells. Taken together, it is speculated that NO-induced autophagy functions as a survival mechanism via AMPK activation against apoptosis in the MC3T3-E1 cells.

• Molecules and Cells
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• 제44권7호
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• pp.493-499
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• 2021

Parkinson's disease (PD) is characterized by a progressive loss of dopamine-producing neurons in the midbrain, which results in decreased dopamine levels accompanied by movement symptoms. Oral administration of l-3,4-dihydroxyphenylalanine (L-dopa), the precursor of dopamine, provides initial symptomatic relief, but abnormal involuntary movements develop later. A deeper understanding of the regulatory mechanisms underlying dopamine homeostasis is thus critically needed for the development of a successful treatment. Here, we show that p21-activated kinase 4 (PAK4) controls dopamine levels. Constitutively active PAK4 (caPAK4) stimulated transcription of tyrosine hydroxylase (TH) via the cAMP response element-binding protein (CREB) transcription factor. Moreover, caPAK4 increased the catalytic activity of TH through its phosphorylation of S⁴⁰, which is essential for TH activation. Consistent with this result, in human midbrain tissues, we observed a strong correlation between phosphorylated PAK4^S474, which represents PAK4 activity, and phosphorylated TH^S40, which reflects their enzymatic activity. Our findings suggest that targeting the PAK4 signaling pathways to restore dopamine levels may provide a new therapeutic approach in PD.

• The Korean Journal of Physiology and Pharmacology
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• 제2권6호
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• pp.743-752
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• 1998

The atrial acetylcholine-activated $K^+\;(K_{ACh})$ channel is gated by the pertussis toxin-sensitive inhibitory G $(G_K)$ protein. Earlier studies revealed that ATP alone can activate the $K_{ACh}$ channel via transphosphorylation mediated by nucleoside-diphosphate kinase (NDPK) in atrial cells of rabbit and guinea pig. This channel can be activated by various agonists and also modulated its function by phosphorylation. ATP-induced $K_{ACh}$ channel activation (AIKA) was maintained in the presence of the NDPK inhibitor, suggesting the existence of a mechanism other than NDPK-mediated process. Here we hypothesized the phosphorylation process as another mechanism underlying AIKA and was undertaken to examine what kinase is involved in atrial cells isolated from the rat heart. Single application of 1 mM ATP gradually increased the activity of $K_{ACh}$ channels and reached its maximum $40{\sim}50$ sec later following adding ATP. AIKA was not completely reduced but maintained by half even in the presence of NDPK inhibitor. Neither ADP nor a non-hydrolyzable ATP analogue, AMP-PNP can cause AIKA, while a non-specific phosphatase, alkaline phosphatase blocked completely AIKA. PKC antagonists such as sphingosine or tamoxifen, completely blocked AIKA, whereas PKC catalytic domain increased AIKA. Taken together, it is suggested that the PKC-mediated phosphorylation is partly involved in AIKA.

• 동의생리병리학회지
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• 제30권1호
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• pp.20-26
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• 2016

Prunellae Spica, the herbaceous plant in the genus Prunella, is a traditional herbal medicine and has been reported to have diuretic, anti-bacterial and anti-oxidant effects. However, the mechanism of its action was not clearly identified. In the present study, we investigated the hepatoprotective effect of Prunellae Spica extract (PSE) against the damage of mitochondria and death in hepatocyte induced by oxidative stress. Treatment of arachidonic acid (AA)+iron significantly induced oxidative stress and apoptosis in the hepatocytes. However, PSE protected cells and inhibited apoptosis by altering the protein levels such as poly(ADP-ribose) polymerase and pro-caspase 3. Moreover, AA+iron induced reactive oxygen species production and mitochondrial dysfunction, and Both of them were inhibited by PSE treatment. PSE markedly activated AMP-activated protein kinase (AMPK), an important regulator in cell survival. Furthermore, this activation by PSE was mediated with liver kinase B1, a major upstream kinase that phosphorylates Thr 172 of AMPKα, and this activation was associated with its cell protection, as assessed by an experiment of a chemical inhibitor. In conclusion, this study demonstrate that PSE protects hepatocytes against oxidative stress as mediated with activation of LKB1-dependent AMPK pathway.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2012년도 춘계 종합학술대회 논문집
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• pp.407-408
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• 2012

요약은 이 연구는 다양한 식이 섭취와 일회 지구성 운동으로 야기되는 근육(백색 비복근) 내 AMP-activated protein kinase(AMPK), Extracellular signal-regulated kinase(ERK 1/2)와 p38 mitogen-activated protein kinase(MAPK)의 신호전달체계를 구명해 보고자 실시되었다. 실험에 사용된 쥐(Sprague-Dawley)는 총 160마리로 크게 일반 탄수화물 식이(CHO; 40마리), 포화지방 식이(SAFA; 40마리), 단일불포화 식이(MUFA; 40마리)와 다불포화 식이(PUFA; 40마리)로 나누어 연구를 진행하였다. 운동 프로그램은 일회 지구성 운동으로 30분 운동 후 5분 휴식의 사이클을 지속적으로 6번 반복하여 총 3시간의 지구성 수영 운동을 실시하였고, 분석을 위한 조직 샘플링은 운동 전, 운동 후 0시간, 1시간, 4시간, 24시간에 걸쳐서 이루어졌다. 연구의 결과는 서로 다른 식이 섭취와 운동에 따른 AMPK의 신호전달 단백질의 발현은 유의한 치이가 나타나지 않았다. 그러나 서로 다른 식이를 섭취한 쥐의 근육에서 ERK 1/2(p<.01)와 p38 MAPK(p<.001)의 신호전달 단백질의 발현은 유의한 차이를 보였다(p<.05). 흥미로운 결과는 운동에 대한 유의한 차이는 AMPK, ERK1/2와 p38 MAPK 모두 유의한 차이를 보이지 않았다는 것이다. 결론적으로 일회 지구성 운동보다 서로 다른 식이의 섭취가 근육 내(백색 비복근)의 대사적 변화를 일으키는데 주도적인 영향을 미칠 수 있음을 시사할 수 있다.

• BMB Reports
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• 제53권5호
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• pp.272-277
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• 2020

Protein kinase CK2 downregulation induces premature senescence in various human cell types via activation of the reactive oxygen species (ROS)-p53-p21^Cip1/WAF1 pathway. The transcription factor "nuclear factor erythroid 2-related factor 2" (Nrf2) plays an important role in maintaining intracellular redox homeostasis. In this study, Nrf2 overexpression attenuated CK2 downregulation-induced ROS production and senescence markers including SA-β-gal staining and activation of p53-p21^Cip1/WAF1 in human breast (MCF-7) and colon (HCT116) cancer cells. CK2 downregulation reduced the transcription of Nrf2 target genes, such as glutathione S-transferase, glutathione peroxidase 2, and glutathione reductase 1. Furthermore, CK2 downregulation destabilized Nrf2 protein via inhibiting autophagic degradation of Kelch-like ECH-associated protein 1 (Keap1). Finally, CK2 downregulation decreased the nuclear import of Nrf2 by deactivating AMP-activated protein kinase (AMPK). Collectively, our data suggest that both Keap1 stabilization and AMPK inactivation are associated with decreased activity of Nrf2 in CK2 downregulation-induced cellular senescence.