JAK1 Kinase Activity Is Required for the Dysregulated JAK1-STAT Pathway to Exacerbate Aberrant Protein Aggregation

Background: Intracellular aberrant protein aggregation (APA) is a hallmark of many forms of human disease. No clinical strategies purposely target APA yet. In a recent study, we have discovered that APA hijacks phosphorylated STATs into protein aggregates thereby decoys and sustains JAK1-STAT activation, which in turn exacerbates APA and proteotoxicity, forming a vicious circle. The objective: of the present study is to further explore the therapeutic implications of this discovery in animals. We hypothesize: that JAK1 inhibition breaks the vicious circle, mitigates the decoyed JAK1-STAT activation, thereby protects against APA and proteotoxicity. Methods: We interrogated JAK1in mice with CryAB R120G (R120G)-based cardiac proteinopathy through Myh6-Cre-driven Jak1 knockout (Jak1-cko) or JAK1 kinase inhibition by Itacitinib and assessed the resultant changes in myocardial proteostasis and disease progression. Results: Western blot analyses showed that Jak1-cko significantly decreased myocardial JAK1 (1.00±0.35 vs. 0.58±0.05, p =0.0170), as well as downstream Ser727-phosphorylated (p-STAT1) (1.00±0.23 vs. 0.40±0.11, p =0.0003) and total STAT1 (1.00±0.15 vs. 0.68±0.19, p =0.0126) proteins in R120G mice; Jak1-cko attenuated the increases of p-STAT1 and total STAT1 in both soluble and insoluble protein fractions. Jak1-cko also attenuated the increases of myocardial ubiquitin conjugates (1.00±0.04 vs. 0.80±0.09, p =0.0034), Natriuretic Peptide A (11.27±4.74 vs. 5.95±2.99, p =0.0348) and B (6.44±0.81 vs. 4.63±0.65, p =0.0010) proteins in R120G mice at 3 months of age, demonstrating that JAK1 plays a major role in the R120G-induced impairment of proteostasis and cardiac pathology.M-mode echocardiography showed that concentric cardiac hypertrophy in R120G mice was markedly alleviated by Jak1-cko, as evidenced that the reduction of left ventricular (LV) end-diastolic volume (53.23±10.08 µL vs. 67.68±10.94 µL, p =0.0162) and the increases in LV posterior wall thickness (0.86±0.08 mm vs. 0.73±0.07 mm, p =0.0230) were attenuated by Jak1-cko.Administration of JAK1 kinase inhibitor Itacitinib (2.4mg/kg/day) via subcutaneous osmotic mini pump for 4 weeks also markedly attenuated the accumulation of insoluble STAT1 (14.08±0.43 vs. 10.56±1.25, p =0.0014) and of insoluble CryAB (1.00±0.05 vs. 0.79±0.05, p =0.0052) in R120G mouse myocardium, indicating that JAK1 kinase inhibition can attenuate APA.Overall, these data suggest that suppressing the sustained phosphorylation of STATs via Jak1 knockout or JAK1 kinase inhibition attenuates APA and proteotoxicity in R120G hearts. Conclusions: This study provides compelling in vivo evidence that JAK1 kinase activity is required for the dysregulated JAK1-STAT pathway to exacerbate APA and proteotoxicity, thereby identifying a potentially new strategy to treat APA-dependent diseases. American Heart Association (AHA) grant (20TPA35490091), AHA Predoctoral Fellowship (23PRE1023108). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.