Browsing by Author "Chen, I-Ping"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Muscle LIM Protein Force-Sensing Mediates Sarcomeric Biomechanical Signaling in Human Familial Hypertrophic Cardiomyopathy
    (American Heart Association, 2022) Riaz, Muhammad; Park, Jinkyu; Sewanan, Lorenzo R.; Ren, Yongming; Schwan, Jonas; Das, Subhash K.; Pomianowski, Pawel T.; Huang, Yan; Ellis, Matthew W.; Luo, Jiesi; Liu, Juli; Song, Loujin; Chen, I-Ping; Qiu, Caihong; Yazawa, Masayuki; Tellides, George; Hwa, John; Young, Lawrence H.; Yang, Lei; Marboe, Charles C.; Jacoby, Daniel L.; Campbell, Stuart G.; Qyang, Yibing; Pediatrics, School of Medicine
    Background: Familial hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease and is typically caused by mutations in genes encoding sarcomeric proteins that regulate cardiac contractility. HCM manifestations include left ventricular hypertrophy and heart failure, arrythmias, and sudden cardiac death. How dysregulated sarcomeric force production is sensed and leads to pathological remodeling remains poorly understood in HCM, thereby inhibiting the efficient development of new therapeutics. Methods: Our discovery was based on insights from a severe phenotype of an individual with HCM and a second genetic alteration in a sarcomeric mechanosensing protein. We derived cardiomyocytes from patient-specific induced pluripotent stem cells and developed robust engineered heart tissues by seeding induced pluripotent stem cell-derived cardiomyocytes into a laser-cut scaffold possessing native cardiac fiber alignment to study human cardiac mechanobiology at both the cellular and tissue levels. Coupled with computational modeling for muscle contraction and rescue of disease phenotype by gene editing and pharmacological interventions, we have identified a new mechanotransduction pathway in HCM, shown to be essential in modulating the phenotypic expression of HCM in 5 families bearing distinct sarcomeric mutations. Results: Enhanced actomyosin crossbridge formation caused by sarcomeric mutations in cardiac myosin heavy chain (MYH7) led to increased force generation, which, when coupled with slower twitch relaxation, destabilized the MLP (muscle LIM protein) stretch-sensing complex at the Z-disc. Subsequent reduction in the sarcomeric muscle LIM protein level caused disinhibition of calcineurin-nuclear factor of activated T-cells signaling, which promoted cardiac hypertrophy. We demonstrate that the common muscle LIM protein-W4R variant is an important modifier, exacerbating the phenotypic expression of HCM, but alone may not be a disease-causing mutation. By mitigating enhanced actomyosin crossbridge formation through either genetic or pharmacological means, we alleviated stress at the Z-disc, preventing the development of hypertrophy associated with sarcomeric mutations. Conclusions: Our studies have uncovered a novel biomechanical mechanism through which dysregulated sarcomeric force production is sensed and leads to pathological signaling, remodeling, and hypertrophic responses. Together, these establish the foundation for developing innovative mechanism-based treatments for HCM that stabilize the Z-disc MLP-mechanosensory complex.
  • Thumbnail Image
    Item
    Tlr2/4‐Mediated Hyperinflammation Promotes Cherubism‐Like Jawbone Expansion in Sh3bp2 (P416R) Knockin Mice
    (Wiley, 2021-10-30) Fujii, Yasuyuki; Monteiro, Nelson; Sah, Shyam Kishor; Javaheri, Homan; Ueki, Yasuyoshi; Fan, Zhichao; Reichenberger, Ernst J.; Chen, I-Ping; Biomedical and Applied Sciences, School of Dentistry
    Cherubism (CBM), characterized by expansile jawbones with multilocular fibrocystic lesions, is caused by gain-of-function mutations in SH3 domain-binding protein 2 (SH3BP2; mouse orthologue Sh3bp2). Loss of jawbone and dental integrity significantly decrease the quality of life for affected children. Treatment for CBM is limited to multiple surgeries to correct facial deformities. Despite significant advances made with CBM knockin (KI) mouse models (Sh3bp2 KI/KI ), the activation mechanisms of CBM lesions remain unknown because mutant mice do not spontaneously develop expansile jawbones. We hypothesize that bony inflammation of an unknown cause triggers jawbone expansion in CBM. To introduce jawbone inflammation in a spatiotemporally controlled manner, we exposed pulp of the first right mandibular molar of 6-week-old Sh3bp2 +/+ , Sh3bp2 KI/+ , and Sh3bp2 KI/KI mice. Bacterial invasion from the exposed pulp into root canals led to apical periodontitis in wild-type and mutant mice. The pathogen-associated molecular patterns (PAMPs)-induced inflammation of alveolar bone resulted in jawbone expansion in Sh3bp2 KI/+ and Sh3bp2 KI/KI mice. CBM-like lesions developed exacerbated inflammation with increased neutrophil, macrophage, and osteoclast numbers. These lesions displayed excessive neutrophil extracellular traps (NETs) compared to Sh3bp2 +/+ mice. Expression levels of IL-1β, IL-6, and TNF-α were increased in periapical lesions of Sh3bp2 +/+ , Sh3bp2 KI/+ , and Sh3bp2 KI/KI mice and also in plasma and the left untreated mandibles (with no pulp exposure) of Sh3bp2 KI/KI mice, suggesting a systemic upregulation. Ablation of Tlr2/4 signaling or depletion of neutrophils by Ly6G antibodies ameliorated jawbone expansion induced by PAMPs in Sh3bp2 KI/KI mice. In summary, successful induction of CBM-like lesions in jaws of CBM mice is important for studying initiating mechanisms of CBM and for testing potential therapies. Our findings further emphasize a critical role of host immunity in the development of apical periodontitis and the importance of maintaining oral health in CBM patients.