Research Projects
Our lab studies physiological organ remodeling across life stages. We investigate tissue remodeling induced by heterogeneous intercellular networks in conjunction with mechanical environment and humoral factors that occur during the life course, such as pregnancy and aging. We also aim to elucidate the interactive mechanisms between maternal organ remodeling and fetal development, and to develop regenerative and anti-aging technologies based on the mechanism of physiological organ remodeling.
Research Topics :
- Maternal organ remodeling during pregnancy
- Mechanism of organ aging
- Development of regenerative and anti-aging technologies base on physiological organ remodeling
- Controlling cell fate transformation in respiratory diseases
1. Maternal organ remodeling during pregnancy
During pregnancy, various maternal organs such as the liver, heart, thymus, brain, and skin undergo physiological changes in morphology and function. The maternal organ remodeling would be essential for the establishment of pregnancy, maternal metabolism, and the fetal development. However, the underlying mechanism remains largely unknown. We aim to elucidate the mechanism and physiological significance of the maternal organ remodeling from the view point of spatiotemporal regulation of tissue cells, stem cell heterogeneity and plasticity, multicellular network, mechanobiology, and maternal-fetal crosstalk.
[Maternal Skin remodeling during pregnancy]
The abdominal skin of maternal body expands rapidly during pregnancy. We have found that epidermal stem cells reside in the basal layer generate highly proliferative Tbx3-positive basal cells (Tbx3+-BCs) during pregnancy to populate the expanding abdominal epidermis. The appearance of Tbx3+-BCs depends on humoral signals such as Igfbp2 secreted by dermal cells (Ichijo et al., Nat Commun. 2017). Lineage tracing analyses showed that Tbx3+-BC clones appeared temporary in the abdominal epidermis during pregnancy, followed by differentiation after parturition. This spatiotemporal appearance of Tbx3+-BCs is caused by dermal angiogenesis, whereby dermal blood vessels increase during pregnancy and return to the basal level after parturition. We showed that mechanical stretch triggers dermal angiogenesis (Ichijo et al., Sci. Adv. 2021).
[Maternal Liver Remodeling during Pregnancy]
The maternal liver expands in gestation, which is believed to be essential for maternal metabolism and fetal growth. The liver remodeling during pregnancy involves the proliferation and hypertrophy of hepatocytes, the parenchymal cells of the liver. We showed that the bile duct epithelial cells, the non-hepatic parenchymal cells of the liver, transiently proliferated and self-renewed in early-mid pregnancy. The proliferation of bile duct epithelial cells is YAP-dependent, and inhibition of YAP function suppresses liver hypertrophy in pregnancy (Koduki et. al., Genes Cells 2021). In addition, we found that hepatocyte proliferation changes spatiotemporally as pregnancy progresses, with specific proliferation of hepatocytes in the portal vein area in mid-pregnancy and in the central vein area in late pregnancy. Furthermore, we found that hepatocyte proliferation in the portal vein region in midpregnancy suppresses maternal hyperglycemia and avoids fetal enlargement (Kozuki et. al., Commun Biol 2023). We are currently investigating the role of nonhepatic parenchymal cells in maternal liver remodeling, as well as the multiorgan and maternal-fetal interactions.
2. Mechanism of organ aging
We are studying the degenerative mechanism of skin in aging and obesity from the viewpoint of tissue stem cells, mechanobiology, and chronic inflammation. Epidermal stem cells deteriorate with aging accompanied with hemidesmosome fragility and misorientation of cell division, which leads to elimination of the stem cells from the basal layer. It has been reported that the epidermal stem cell aging is caused by intrinsic cues such as DNA damage induced by oxidative stress. However, the age-related changes in the environment surrounding epidermal stem cells and their effects on epidermal stem cells have not been elucidated. We found that age-related stiffening of the dermis induces long-term activation of the mechano-sensing ion channel Piezo1 in epidermal stem cells, which causes prolonged calcium flux to induce premature differentiation, hemidesmosomes fragility, and misorientation of division of epidermal stem cells. Age-related dermal stiffening is caused by a decrease in dermal blood vessels, and Ptx3 secreted from fibroblasts was identified as a humoral factor that induces vasculature atrophy in aging (Ichijo et. al., Nature Aging 2022) . Because Ptx3 accumulates also in the skin of the elderly, it may be one of the causes of skin aging in humans.
3. Development of regenerative and anti-aging technologies based on physiological organ remodeling
The dynamics of tissue stem cells during pregnancy is similar to that of stem cells during repair from injury and embryonic development. The highly proliferative Tbx3+-BCs found in the abdominal skin epidermis of pregnant mice are abundant in the developing fetal skin epidermis (Ichijo et. al., Genes Cells 2017). The Tbx3+-BCs also appear during wound healing, and knocking out Tbx3 in the epidermis delays wound healing. In addition, administration of dermal humoral factors that induce Tbx3+-BCs accelerates wound healing (Ichijo et al., Nat Commun. 2017). Stem cell proliferation associated with pregnancy does not induce tumorigenesis and returns to a steady state after parturition. In addition, skin vasculature expands during pregnancy, while regress in ageing. Taking advantage of this property, we are developing regenerative and anti-aging technology based on the mechanism of physiological organ remodeling.
4. Controlling cell fate transformation in respiratory diseases
The primary epithelial cells in the alveoli—type I epithelial cells (AT1) and type II epithelial cells (AT2)—differ greatly in their structure and function. AT1 cells cover 95% of the alveolar surface area and are responsible for gas exchange. AT2 cells secrete surfactant into the lumen to regulate alveolar surface tension and are also known to function as tissue stem cells. It is known that when injury is induced in the alveoli, the stem cell program of AT2 cells is activated, leading to cell proliferation and differentiation into AT1 cells; however, the state of the cells during this transitional process has not been thoroughly discussed. Using single-cell transcriptome analysis, cell lineage tracing in genetically engineered mice, and organoid techniques, we discovered that cells in the process of differentiation exist in a unique cell state—distinct from both AT1 and AT2—referred to as the pre-AT1 transitional cell state (PATS) (Kobayashi et al., Nat Cell Biol. 2020). Furthermore, we found that while PATS cells disappear upon the successful completion of normal repair, they persist and accumulate in chronic respiratory diseases. However, the branching point between the pathway leading to normal repair and that leading to chronicity and accumulation—that is, the state of the cell fate transition and its regulatory factors—remains not well understood at present. Currently, we are working on establishing high-resolution analytical methods at the transcriptome and epigenome levels, chronicity mouse models, and innovative lung cell culture techniques, and are applying these approaches to address the aforementioned questions.
We are also working on a new mechanism of action for α1-antitrypsin deficiency, which causes COPD (Park et. al., J. Biol. Chem., 2025)。
Previous Research
Mechanism of oriented cell division
In various organs of multicellular organisms, cells divide along a predetermined axial direction. This oriented cell division plays an essential role in stem cell differentiation and tissue morphogenesis. Our laboratory has been studying the mechanism by which adhesion to extracellular matrix determines the axis of cell division using cultured cells. We found that when adherent cells were cultured on an extracellular matrix such as fibronectin, the mitotic spindles are oriented parallel to the substrate. This spindle orientation depends on integrin beta1 and promotes adhesion of both daughter cells to the substrate after cell division (Toyoshima et. al., EMBO J., 2007). It was found that the cell membrane phospholipid PIP3 concentrates the dynein motor protein in the central region of the cell surface in an actin regulator Cdc42-dependent manner, and equilibrates the traction force exerted on the mitotic spindle with respect to the substrate (Toyoshima et. al., Dev. Cell, 2007; Mitsushima et. al., Mol. Cell Biol., 2009). Genome-wide screening was performed using the siRNA library and identified novel regulators for spindle orientation. Among them, ABL1 directly phosphorylates the spindle orientation regulator NuMA(Matsumura et. al., Nat. Commun., 2012), and PCTK1 regulates the spindle axis via PKA-MyosinX-integrin module (Iwano et. al., Mol. Cell Biol., 2015). We revealed that extracellular matrix geometric information is transmitted to the spindle orientation regulatory complex Gα / LGN / NuMA via caveolin1 (Matsumura et. al., Nat. Commun., 2016). The cell division axis is important for the symmetric and asymmetric divisions of stem cells. We reported that during differentiation of mouse ES cells into mesoderm and endoderm, a division axis regulator mInsc, is transiently upregulated in a transcription factor c-Rel-dependent manner, which promotes mesodermal differentiation (Ishibashi et. al., J. Biol. Chem., 2016).
