/Research
Biological functions are intricately regulated by the homeostasis of genome content and daily rhythmicity, with profound implications for overall physiological processes and health. Imbalances in these systems can lead to various disorders, including metabolic diseases, compromised brain function, and tumorigenesis. Our long-term research focuses on unraveling the mechanisms governing genome content oscillation within polyploid tissues and the complex interplay between environmental stresses and genome content integrity. Through this work, we aim to achieve a comprehensive understanding of the consequences resulting from disruptions in these regulatory mechanisms across a spectrum of pathophysiological functions, ultimately impacting human health.
生物功能受到基因組含量和日常節律的動態平衡所調控，對整體生理過程和健康具有深遠的影響。這些系統的失衡可能導致多種疾病，包括代謝性疾病、大腦功能受損和腫瘤形成等...。我們的長期研究專注於揭示多倍體組織內基因組含量振盪的調控機制，以及環境壓力、生物時鐘與基因組含量完整性之間的複雜相互作用所導致的慢性疾病，例如: 肝臟相關代謝症候群、脂肪肝、肝癌和腦腸軸線失調症候群。通過這項工作，我們旨在全面瞭解這些調控機制受干擾後對於生理功能及病理形成的影響，從而進一步瞭解影響人類健康的相關機制以及可能的臨床應用策略。
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The going on projects:
(1) To evaluate the unknow functions of intrinsic circadian clock in mammals.
(2) To study the interplay between circadian clock and polyploidization and its reversal in polyploid tissue.
(3) To understand the impact of genome content oscillation on biological and pathological meanings.
Time is an integral part of our life. Most organisms on the earth show daily cycles of physiology and behavior in harmony with light-dark cycles in the environment. Endogenous time is generated by a self-sustained molecular oscillator composed of a transcriptional-posttranscriptional feedback loop in which clock genes regulate their own transcription. This core oscillator couples to cell metabolism and maintains proper rhythms in endocrine and metabolic pathways required for homeostasis of organisms.
The daily behavior of mouse shows circadian rhythm (left figure), which is entrained by external stimulation like light-dark cycle. In the dark-dark cycle environment, the internal clock maintains animal under a correct circadian rhythm (close to 24 hours) to keep normal physiological homeostasis. However, in the circadian clock genes deficient mice (right figure), the internal clock is loss of function. The mouse circadian behavior can be entrained by external light-dark cycle, but it shows arrhythmic behavior under constant dark area.
Liver is particularly important as a central organ for glucose, lipids and nucleotides metabolism in the body. The circadian clock rhythmically regulates genomic and epigenetic processes to anticipate and adapt to cycles of feeding that have dramatic consequences on metabolic activity. Since liver is the primary organ to which all nutrients and toxins are conveyed from the intestine via portal vessels, homeostatic renewal of hepatocytes is essential for its maintenance.
Histologically, liver is composed by centrilobule, middle lobule, and periportal lobule regions. Centrilobule is the region surrounding central vein (CV), while periportal lobule surrounds portal triad. Midzonal lobule is located between centrilobule and periportal lobule. In WT liver, hepatocytes distributed along CV-PV axis exhibit specialization in morphology, genetic content, and metabolic function, which is called liver zonation. In circadian genes deficient mice, an uncanny phenotype was observed that is karyomegaly around CV region.
Actually, deficiency of circadian clock gene has been demonstrated to impair the function of almost all of our body system and promote tumorigenesis. In our previous study, we found Period 1, 2, 3, genes TKO mice show enlarged nuclear size in the liver, due to impaired mitogen-activated protein kinase phosphatase 1 (Mkp1)-mediated circadian modulation of the extracellular signal-regulated kinase (Erk1/2) activity [1]. These data provide clear evidence that the circadian clock not only orchestrates dynamic changes in metabolic activity, but also regulates homeostatic self-renewal of hepatocytes through Mkp1-Erk1/2 signaling pathway.
After three month of DEN injection, it is difficult to see tumor nodules on the liver surface. But, after three month of DEN injection, a number of microscopy foci can be identified in the liver, and, these foci are usually composed by around hundred of cells. Notable, a lot of preneoplastic foci is enriched nearby central vein marker (magenta). And, quantitative data also show that centrilobule and midlobule regions are the dominant area to detect the preneoplastic focis. This is highly consistent with the distribution of hyperpolyploidy hepatocytes (the white arrows), suggesting that hyperpolyploidization of hepatocytes may play a critical progression to transform normal hepatocyte into preneoplastic cells. It’s very interesting, the cells in preneoplastic foci (H&E staining images) and in the tumor nodule derived from centrilobular hepatocytes always have smaller nucleus size, comparing with the normal hepatocytes. Because multipolar dividing are frequently observed in preneoplastic foci and tumor nodules, we hypothesize, polyploidy reversal maybe a critical step to make hyperpolyploid hepatocytes become a cancer cells.
Under genotoxin, organic chemistry or high-fat diet treatment, hyperpolyploid hepatocytes will be generated within midlobule and centrilobule regions through upregulation of AurkB-mediated abscission failure. This pathological change would be the origin for the initiation of preneoplastic cells through polyploidy reversal pathway and generate the preneoplastic cells with low-plyploidy state.
Notably, circadian dysfunction has been demonstrated to induce NAFLD prior to spontaneous hepatocarcinogenesis in the liver [2]. Recent study also revealed that highly polyploid hepatocytes in human liver are associated with worse prognosis of HCC tumors [3]. Yet, how these hyperpolyploid hepatocytes are generated, and the pathophysiological function or consequence of hepatic hyperpolyploidy remains an unanswered question of medical importance. We sough to further define the origin and function of hyperpolyploid hepatocytes and their clinical implications. To address this question, mice were treated with genotoxins, and hyperpolyploid hepatocytes were discovered predominantly around central vein region, which displayed a similar phenotype in Per-TKO mouse liver. In this study, we revealed that, after genotoxin-induced carcinogenic liver injury, hyperpolyploid hepatocytes arising from abscission failure are oncogenerative cells and a major source of preneoplastic lesions. Our findings have answered two fundamental questions :
-- Where is the critical region to generate preneoplastic lesions in the liver
-- How can hepatocytes transform into preneoplastic cells during the initiation of tumorigenesis in the liver.
A significant contribution in the understanding the correlation between genomic content switch and cancer biology will be our long-term goal in the future.