Yang Liangdong

Biography

During Dr. Yang’s postdoctoral training, he studied Notch signaling, a lateral inhibition system that controls cell fate determination, at UCLA. He studied how Notch signaling is regulated by glycosylation, ubiquitin/proteasome, and endocytosis, and he uncovered the mechanism of differential Notch signaling activation by Fringe family proteins (Notch signaling modifiers). Then, he moved on to study TGFb/BMP signaling in cranial facial development, especially palatogenesis, at USC. He made two knock-in mice to study the mechanisms underlying cleft palate in in vivo system. Coming back to NHRI at Taiwan, He studied regeneration of the skin and hair follicle. The primary projects conducted during his PI position are as follows: 1. Study on the role of Notch signaling in the epidermal and hair cycle homeostasis The skin serves as a barrier to prevent the loss of body fluid and defend against external stimuli. Notch signaling has been demonstrated to regulate basal keratinocyte differentiation, which is important for building up the epidermal barrier. However, the neonatal lethality of mutant mice prevents postnatal study. To bypass the problem, we conditionally deleted common Notch signaling components (Pofut1 and Rbpj) in the suprabasal layer of the epidermis and in the hair follicle lineages using the Tgfb3-Cre deleter line. We found that Notch signaling is required for late stage epidermal differentiation and proper regulation of the hair cycle; Pofut1-deficient hair follicles displayed a delay in anagen initiation and disrupted catagen-telogen transition during the hair cycle. These findings showed that Notch signal deficit can be at the basis of postnatal skin and hair follicle disorders. 2. Study on the role of TGF-β signaling in hair cycle homeostasis. The hair follicle is a miniorgan for studying regenerative medicine, and previous animal studies have implicated TGF-βs in hair cycle control. Murine epidermal stem cells located at the bulge region are responsible for replenishing the hair lineage, while the stem cells located at the isthmus regenerate interfollicular epidermis and sebaceous glands. To analyze the role of TGF-β signaling in distinct stage of the hair cycle, we employed a triple transgenic animal model utilizing a combined Cre/loxP and rtTA/TRE system to allow inducible and reversible inhibition of TGF-β signaling in hair follicle lineages. We found that TGF-β signaling does not prevent catagen progression; however, it induces 1) aberrant proliferation and differentiation of isthmus stem cells to epidermis and sebocyte lineages; 2) a blockade in bulge stem cell activation; 3) an incomplete hair shaft development. Our results showed that TGF-β signaling plays an important role in regulating distinct epithelial stem cell populations in hair follicles. 3. Study on the role of Notch signaling in mouse conducting airways during postnatal development The airway epithelium serves as a major defense barrier and proper differentiation of the airway epithelium into ciliated, neuroendocrine, secretory Clara and goblet cells is crucial to maintain the barrier. Goblet cell metaplasia and mucus overproduction contribute to the pathogenesis of chronic lung diseases, including asthma and chronic obstructive pulmonary disease (COPD). During the course of analyzing the gene recombination pattern induced by Tgfb3-Cre mouse line, we found a mosaic recombination pattern in the lung epithelium. We therefore collaborated with Dr. Po-Nien Tsao from Children’s Hospital, NTU to investigate the lung phenotype resulted from conditional inactivation of Pofut1 using Tgfb3-Cre mice. Mutant mice displayed marked goblet cell metaplasia, as well as decreased Clara cells and increased ciliated cells. Lineage study in vivo suggested that goblet cells originated from a sub-population of Notch signaling-deficient Clara cells largely present in proximal airways. Our data indicate that Notch signaling is required to prevent Clara cells from differentiating into goblet cells in postnatal airway epithelium. 4. Study on the molecular function of Gsdma3, a gene involved in skin inflammation and hair loss. At least nine mutations in the mouse gasdermin A3 gene have been characterized and these mutations are loacted at the C-terminal part of the protien. Mutant mice displayed progressive skin inflammaiton and the underlying cause remians unclear. We then studied the mode of action of Gsdma3 using the cell culture system. We showed that Gsdma3 is regulated by an intramolecular foldback inhibition mechanism: the dominant mutations located at the C-terminal domain disrupt the self-association. The unmasked N-terminal functional domain of Gsdma3 is targeted to mitochondria by Hsp70/Hsp90 via Tom70, where it causes mitochondrial dysfunction and necrotic cell death. Our data suggest that deregulated Gsdma3 activity may sensitize keratinocyte to necrosis and inflammation via tageing mitochondrial function. Gsdma3-mediated cell death is a programmed cell necrosis. 5. Study on the biological function of Gsdma3, a gene involved in skin inflammation and hair loss. Human GSDMA is genetically associated with asthma, and the function of GSDMA in the skin remains unclear. Autosomal dominant mutations in gasdermin A3 (Gsdma3), an ortholog of GSDMA in mice, caused progressive epidermal hyperplasia and hair loss. To test the hypothesis that Gsdma3 gain-of-function causes autosomal dominance of Gsdma3, we generated a doxycycline-inducible mouse model to express Gsdma3 in the epidermis. We found that induced expression of Gsdma3 in the basal keratinocytes caused epidermal hyperplasia, inflammatory infiltrations, and hair cycle defect after depilation, the phenotypes similar to those reported in Gsdma3 mutant mice. Moreover, we found that induced expression of Gsdma3 in primary keratinocytes caused spontaneous necrosis and leakage of intracellular components. Our data suggest that the dominant mutations in Gsdma3 are gain-of-function mutations. Thus, the Gsdma3-mediated programmed cell death may contribute to epithelial barrier immunity to defend against external stimuli. With two papers recently published in Nature relating gasdermin D to pyroptosis (inflammatory cell necrosis) in macrophage and endothelial cells, our data indicated that an innate immune-mediated mechanism could underlie the skin inflammation phenotype and that repetitive unresolved inflammation may lead to chronic inflammatory diseases.

Research Interest

The research interests of Dr. Yang are Notch and TGF-beta signaling pathways, and how these signaling pathways regulate developmental processes and tissue homeostasis. He is currently studying the role of TGF-beta and Notch signaling in epithelial cells of the skin and hair follicle stem cells The epidermis protects the body from environmental insults and also prevents the loss of body fluid. Impaired epidermal stratification often leads to skin disease, such as ichthyosis vulgaris and atopic dermatitis, and abnormality in hair cycle regulation commonly results in alopecia in humans. Epidermal stratification starts from proliferating basal keratinocytes which move upward and differentiate to suprabasal layers, followed by terminal maturation to stratum corneum providing the barrier function. The hair follicle cycles through anagen (growth phase), catagen (regression phase), and telogen (resting phase) throughout the adult life. In both cases, homeostasis is maintained by distinct stem cells which give rise to cell populations of epidermal lineage and follicular lineage. His long term research interest is to study the molecular mechanisms underlying epidermal barrier formation and the niche signals which maintain the self-renewal and multilineage differentiation of hair follicle stem cells. Dr. Yang will apply molecular biology, cell biology, and mouse conditional knockout studies to accomplish his research interests.