Abstract Body: Chaperone proteins like αB-Crystallin (CRYAB) maintain protein quality in cardiomyocytes, preventing protein aggregation such as Desmin. A human iPSC model with CRYAB-R120G mutation previously revealed desmin aggregation and contractile dysfunction in 3D micro-heart tissues (µHT). JAK/STAT pathway inhibition in 2D culture cleared DRM-related aggregates, prompting testing of JAK1 inhibitor Itacitinib for therapeutic benefits.

Methods: iPSC-cardiomyocytes (iPS-CMs) from Wild Type (WT) and DRM mutant (R120G) lines were used to form µHT in PDMS microwells with posts of varying stiffness (3 MPa or 640 kPa). iPS-CMs were transduced with AAV6-encoded RGECO1.2 for Ca2+ handling assessment. µHT were treated for 7 days with Itacitinib (0.1 or 1µM) or 0.1% DMSO vehicle control.

Results: High afterload (stiff posts) worsened DRM µHT contractile dysfunction, especially at higher pacing frequencies, mirroring DRM patient exercise intolerance. The RGECO1.2 indicator revealed dysfunction was linked to reduced calcium intake (Fig. 1). Elevated STAT1 phosphorylation (pY701) in R120G µHT was reduced by Itacitinib. Whereas low-dose Itacitinib improved contractility in DRM and control µHT at 2Hz, a higher dose (1µM) depressed contractility in both genotypes. (Fig. 2).

Our findings indicate JAK1 inhibition can partly rescue DRM-associated contractile dysfunction but suggest some JAK/STAT signaling is necessary for normal contractile function.