Iwata Lab

This project explores the impact of non-coding RNAs and cholesterol metabolism on craniofacial development, particularly cleft palate, which affects 1 in 700 births globally. It focuses on how environmental factors and genetic mutations influence the expression of non-coding RNAs and the disruption of cholesterol metabolism, both of which have been linked to craniofacial anomalies like cleft palate through various syndromes and metabolic disturbances. The research aims to enhance understanding of these mechanisms, contributing to the development of therapeutic strategies for diagnosing and preventing craniofacial deformities. Additionally, the project investigates how cholesterol metabolism affects craniofacial bone formation, particularly through the differentiation and function of osteoblasts and osteoclasts, potentially offering new treatments for bone diseases. The creation of a new searchable database for genetic and epigenetic factors related to these deformities supports the project’s comprehensive approach to addressing craniofacial developmental defects.

Cholesterol metabolism: Human linkage studies have shown that genetic mutations related to cholesterol metabolism or abnormal maternal cholesterol diets lead to craniofacial deformities such as cleft palate. However, it is mainly unknown how disturbances in cholesterol production result in cleft palate. For instance, mutations in genes involved in cholesterol synthesis (SC5D, DHCR7, and DHCR24) have been found in lathosterolosis, Smith-Lemli-Opitz Syndrome [SLOS], and desmosterolosis. Patients with these syndromes display craniofacial abnormalities (e.g., cleft palate) with a wide array of degrees in severity. In addition, high-cholesterol diets during pregnancy are known to be a risk factor for congenital disabilities, including various craniofacial abnormalities. Sterol-C5-desaturase (SC5D) catalyzes the dehydrogenation of a C-5(6) bond in a sterol intermediate during compound cholesterol biosynthesis. Mutations in SC5D result in cholesterol deficiency as well as excessive lathosterol. This cholesterol precursor causes lathosterolosis, characterized by craniofacial deformities such as cleft palate, dysmorphism, micrognathia, and limb anomalies. By contrast, mutations in DHCR7, which encodes 7-dehydrocholesterol reductase, lead to SLOS, which is characterized by less severe craniofacial deformities (e.g., high-arched palate, less frequent cleft palate, ptosis, a short nasal root) compared with lathosterolosis. These findings suggest that accumulated cholesterol precursors lathosterol and 7-dehydrocholesterol differently interfere with the process of craniofacial development. Thus, while proper regulation of cholesterol metabolism is crucial for craniofacial development, the exact mechanism of how cholesterol metabolism affects craniofacial development remains largely unknown. The results of this study will enhance our understanding of the role of cholesterol metabolism in lip and palate development and will enable us to design future therapeutic approaches to diagnose and prevent cleft lip and palate.
 

Reviewed in Iwaya C, Suzuki A, and Iwata J (2023) MicroRNAs and gene regulatory networks related to cleft lip and palate. International Journal of Molecular Sciences. 2023,24(4),3552. PMID: 36834963.

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Cholesterol metabolism: Human linkage studies have shown that genetic mutations related to cholesterol metabolism or abnormal maternal cholesterol diets lead to craniofacial deformities such as cleft palate. However, it is mainly unknown how disturbances in cholesterol production result in cleft palate. For instance, mutations in genes involved in cholesterol synthesis (SC5D, DHCR7, and DHCR24) have been found in lathosterolosis, Smith-Lemli-Opitz Syndrome [SLOS], and desmosterolosis. Patients with these syndromes display craniofacial abnormalities (e.g., cleft palate) with a wide array of degrees in severity. In addition, high-cholesterol diets during pregnancy are known to be a risk factor for congenital disabilities, including various craniofacial abnormalities. Sterol-C5-desaturase (SC5D) catalyzes the dehydrogenation of a C-5(6) bond in a sterol intermediate during compound cholesterol biosynthesis. Mutations in SC5D result in cholesterol deficiency as well as excessive lathosterol. This cholesterol precursor causes lathosterolosis, characterized by craniofacial deformities such as cleft palate, dysmorphism, micrognathia, and limb anomalies. By contrast, mutations in DHCR7, which encodes 7-dehydrocholesterol reductase, lead to SLOS, which is characterized by less severe craniofacial deformities (e.g., high-arched palate, less frequent cleft palate, ptosis, a short nasal root) compared with lathosterolosis. These findings suggest that accumulated cholesterol precursors lathosterol and 7-dehydrocholesterol differently interfere with the process of craniofacial development. Thus, while proper regulation of cholesterol metabolism is crucial for craniofacial development, the exact mechanism of how cholesterol metabolism affects craniofacial development remains largely unknown. The results of this study will enhance our understanding of the role of cholesterol metabolism in lip and palate development and will enable us to design future therapeutic approaches to diagnose and prevent cleft lip and palate.

Reviewed in Suzuki A, Sangani DR, Ansari A, and Iwata J (2016) Molecular mechanism of midfacial developmental defects. Developmental Dynamics, Mar;245(3):276-93. PMID: 26562615.

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Craniofacial skeletal defects, a significant area of genetic disorders, are still shrouded in mystery. Our study, delving into cholesterol metabolism in craniofacial skeletal development, promises to shed new light on these defects and revolutionize the therapeutics of various bone diseases.

Primary cilia in osteoblasts: Human linkage studies have shown that genetic mutations related to cholesterol metabolism and high maternal cholesterol diets result in craniofacial bone deformities, suggesting cholesterol metabolic aberrations may be a widely conserved mechanism in craniofacial developmental defects. However, how altered cholesterol metabolism causes craniofacial bone abnormalities remains largely unknown. Therefore, our study aims to define how cholesterol metabolic aberrations cause osteoblast and osteoclast differentiation abnormalities and to test the functional significance of downstream target molecules during craniofacial bone formation and homeostasis. The long-term goal of this project, which is to gain insight into the mechanisms of craniofacial bone formation and homeostasis, is also to provide new medications and diagnostic tools for bone diseases, offering hope for the future.
Reviewed in Suzuki A and Iwata J (2021) Amino acid metabolism and autophagy in skeletal development and homeostasis. Bone. 2021 May;146:115881. PMID: 33578033.

Reviewed in Suzuki A, Minamide M, Iwaya C, Ogata K, and Iwata J (2020) Role of metabolism in bone development and homeostasis. International Journal of Molecular Sciences. 2020 Nov 26;21(23):8992. PMID: 33256181. This review article was selected as one of the Top Downloaded Paper of IJMS in 2020.

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Exosomes in osteoclasts: It is known that cholesterol depletion by chemicals (e.g., statins and cyclodextrin) results in osteoclast defects in differentiation and functions. In contrast, mice with hypercholesterolemia or high-fat diets reduce bone formation by promoting osteoclastogenesis. Ovariectomized (OVX) mice exhibit enhanced bone resorption and bone loss due to estrogen deficiency, but interestingly, simvastatin treatment can improve bone loss by normalizing osteoclast activity. Thus, previous studies suggest that the cellular cholesterol in osteoclasts positively influences bone resorption by enhancing osteoclast activity. However, it remains unknown how cholesterol influences osteoclast differentiation and functions. In this study, we investigate how cholesterol is involved in the differentiation and function of osteoclasts during bone formation and homeostasis.

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This project investigates two significant inherited dental conditions: amelogenesis imperfecta and tooth agenesis. Amelogenesis imperfecta, affecting 0.5% of the global population, leads to defective tooth enamel that is thin, soft, and discolored, causing social embarrassment, pain, and early tooth loss. This study explores the role of microRNAs and autophagy in enamel formation, particularly how defects in ameloblast differentiation contribute to the condition. For tooth agenesis, which affects 2-10% of the population excluding third molars, the research focuses on identifying genetic factors and understanding how disruptions in cholesterol metabolism could influence dental development. The project aims to elucidate the complex genetic interactions behind these conditions, potentially leading to new diagnostic tools and treatments for affected individuals and families.

Amelogenesis imperfecta:

Inherited tooth enamel defects (a.k.a. amelogenesis imperfecta) occur worldwide with a prevalence of 0.5%. Significant clinical impacts include social embarrassment, dental pain, eating difficulties, and early tooth loss due to abnormally thin, soft, fragile, and discolored enamel, together with poor aesthetics and functionality. Although amelogenesis imperfecta is a significant and urgent dental issue, the etiology of amelogenesis imperfecta remains unknown, mainly owing to potential complex genetic interactions. We have recently reported that microRNAs (miRNAs), short non-coding RNAs that regulate the expression of target genes at the post-transcriptional level, play a crucial role in regulating genes associated with ameloblast differentiation in humans and mice. In addition, we found that mice with autophagy deficiency displayed amelogenesis imperfecta due to a failure in ameloblast differentiation. Although many studies indicate that autophagy-related molecules are essential in various cellular processes, including transcriptional regulation in physiological and pathological conditions, the transcriptional mechanism regulating differentiation remains unclear. This study will identify a novel mechanism for amelogenesis imperfecta and help develop diagnostic tools and therapeutic interventions in at-risk populations and families.

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Tooth agenesis: Tooth agenesis (a.k.a. missing teeth) occurs with a prevalence of approximately 2–10% (excluding the third molars) worldwide; a missing third molar is more common, occurring at a rate of approximately 20% worldwide. Although tooth agenesis is a significant and urgent dental issue, the etiology of tooth agenesis remains unknown, mainly owing to potential complex genetic interactions. As of today, human genetic studies have identified genetic susceptibility to tooth agenesis in various populations and ethnic groups. Although recent technological advancements have contributed to discovering several novel genetic mutations associated with tooth agenesis, these genes' regulatory networks remain unclear. Interestingly, several cholesterol metabolic syndromes are characterized by dental deformities; however, it remains unclear how altered cholesterol metabolism leads to dental abnormalities. This study aims to define how cholesterol metabolic aberrations cause dental abnormalities and test the functional significance of downstream target molecules during tooth formation.

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This project focuses on understanding the pathogenesis of Sjögren’s disease (SjD), a chronic autoimmune condition affecting the exocrine glands, particularly the salivary and lacrimal glands. By utilizing newly developed animal models for SjD, the research aims to investigate how disruptions in exocytosis and excessive cholesterol synthesis in salivary gland tissues contribute to the disease. The study seeks to unravel the early pathological events that precede clinical symptoms, which could lead to earlier diagnosis and better therapeutic strategies. Additionally, the research explores the complex process of salivary gland development, examining the interactions of various cell types and signaling pathways essential for glandular architecture and function. This comprehensive approach may significantly enhance our understanding of SjD and improve diagnostic and treatment options for those at risk.

Sjögren’s disease: Sjögren’s disease (SjD) is a chronic autoimmune disease characterized by immune cell infiltration of the exocrine glands, mainly the salivary and lacrimal glands. The differential diagnosis and etiology of SjD are extensive since several diseases have similar symptoms and various factors associated with SjD. The current diagnostic criteria for SjD consists of a combination of histological examinations (biopsy) of minor SGs for immune cell foci, serology for autoantibodies, and dry eye/mouth evaluation; therefore, there is no single test that will confirm a diagnosis for SjD. Since patients are diagnosed only at later stages of the disease, the earlier events before clinical manifestations are mainly unknown. Taking advantage of our newly developed SjD animal models, we aim to determine how disruption in exocytosis leads to SjD and how excessive cholesterol synthesis in salivary gland tissues leads to SjD. This research has the potential to significantly advance our understanding of the mechanisms of SjD, leading to the identification of novel targets for therapeutics and new diagnostic tools for identifying SjD at an early pathological stage in at-risk populations.

Reviewed in Iwaya C and Iwata J (in press) Associations between metabolic disorders and Sjogren’s disease. Japanese Dental Science Review.
Reviewed in Suzuki A and Iwata J (2018) Molecular regulatory mechanism of exocytosis in the salivary glands. International Journal of Molecular Sciences. 2018 Oct 17;19(10):3208. PMID: 30336591.

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Salivary gland development: Salivary gland development is a complex process that involves the interactions of multiple cell types, including epithelial, mesenchymal, endothelial, and neuronal cells. Various pathways cooperate to establish acinar and ductal growth, ganglia development, and progenitor cell survival/proliferation. Several mouse genetic studies indicate that these molecular pathways act within complex signaling networks, which require an interdisciplinary approach to elucidate how they affect the different morphogenic processes. Further advances in human genetics and the ever-increasing number of mouse models generated will significantly increase our knowledge of the mechanisms by which signaling pathways and cells establish the tissue architecture and function during salivary gland formation.

Reviewed in Suzuki A, Ogata K, and Iwata J (2021) Cell signaling regulation in salivary gland development. Cellular and Molecular Life Sciences. 2021 Jan 15. PMID: 33449148.

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Adult regenerative myogenesis is vital for restoring normal tissue structure after muscle injury. Muscle repair depends on progenitor satellite cells, which increase in response to injury, and their progeny differentiate and undergo cell-cell fusion to form regenerating myofibers. Myogenic progenitor cells must be precisely regulated and positioned for proper cell fusion. We previously reported that WNT signaling is regulated spatiotemporal-specific during muscle development (Mol Cell Biol, 2015; Sci Rep, 2018). We are further investigating how this signaling pathway regulates muscle development and regeneration. Our long-term goal is to better understand the mechanisms of muscle development and repair, to develop therapeutic interventions for muscle injury and diseases/disorders, and to devise potential strategies to prevent muscle developmental defects and accelerate muscle regeneration, which could have a significant impact on public health and quality of life.