In vivo screening identifies three proteins that may prevent heart failure  

Heart failure is a syndrome of impaired cardiac circulation caused by the inability of the heart to adequately drain the venous return blood volume out of the heart due to impaired systolic and/or diastolic function, resulting in stagnation of blood in the venous system and inadequate perfusion of blood in the arterial system. It is a leading cause (one of the leading causes) of death and disability worldwide, affecting approximately 64 million people worldwide. However, there is still no effective clinical treatment for heart failure, and patients have a mortality rate of up to 50% within 5 years, so there is an urgent need to develop new treatments.

Aug. 31, 2022—Researchers at the International Centre for Genetic Engineering and Biotechnology (ICGEB), King's College London and other institutions have published a paper in the Science subjournal Science Translational Medicine titled: Cardioprotective factors against myocardial infarction selected in vivo from an AAV secretome library.

The study developed a protein "search engine" called FunSel that uses adeno-associated virus (AAV) encoding the mouse secretome for in vivo systematic functional screening of protective factors against myocardial infarction and identified three proteins—Chrdl1, Fam3c, and Fam3b—that protect cardiac function and prevent heart failure after a heart attack by promoting autophagy and cell survival and inhibiting fibrosis.

The team's previous work demonstrated that it is possible to identify factors that protect skeletal muscle fibers using in vivo screening with AAV vectors1, so they wanted to further develop this approach so that it could be applied to a larger scale of systematic automated screening by creating a library corresponding to all secreted factors (secretome) and using this library directly to screen for factors that protect against acute myocardial ischemia. To achieve these aims, they developed the Cardiac FunSel.

A set of 50 vectors from the AAV9 cDNA library was generated in a single pass, and this set was then injected into the hearts of mice at relatively low titers, followed by induction of myocardial infarction. Most of the heart cells die, but those expressing the protective factor survive. Three weeks later the DNA barcodes in the viral genome were detected by second-generation sequencing, leading to direct identification of each factor. The top 7 factors identified by the screening were the 5 unreported cardiac function-related factors Fam3b, Fam3c, Nhlrc3, Chrdl1, HtrA, and the 2 reported factors Mdk and Rln-1.

The team found that Chrdl1 significantly inhibited apoptosis and significantly activated autophagy in cardiac myocytes. Moreover, Fam3b and Fam3c also significantly induced autophagy and resisted apoptosis, suggesting that induction of autophagy may be a major mechanism for protection against myocardial infarction.

Next, the team wanted to investigate the molecular mechanisms by which Chrdl1 exercised its ability to protect cardiomyocyte function. While members of the Chordin family have been reported to bind extracellular BMPs and prevent their binding to receptors, the team found that Chrdl1 can inhibit BMP4 signaling in cardiomyocytes in a dose-dependent manner, and that BMP4 can inhibit the level of background autophagy. Thus, Chrdl1 induces autophagy levels in cardiomyocytes by inhibiting BMP4 signaling.

In addition to cardiomyocyte protection and maintenance of myocardial content, the team noted that Chrdl1-treated post-infarction hearts were smaller in size, suggesting that Chrdl1 may have functions that act on other cells in addition to cardiomyocytes.

A major factor that regulates the response to myocardial injury is TGF-? which stimulates the transdifferentiation of cardiac fibroblasts into?-SMA-positive myofibroblasts. Because of the extensive interactions between the BMP signaling pathway and the TGF-? signaling pathway, the team wondered whether Chrdl1 would directly affect TGF-? signaling. It was found that Chrdl1 could interact with TGF-?1 and inhibit TGF-?1 signaling, thereby suppressing its induction of myocardial fibrosis and myofibroblast transdifferentiation. Thus, in addition to acting on cardiomyocytes to activate autophagy and protect cell survival, Chrdl1 can also act on cardiac fibroblasts to inhibit myocardial fibrosis and pathological remodeling by binding to and inhibiting TGF-?1.

In summary, this study developed a new in vivo screening method, FunSel, and identified that Chrdl1 can induce autophagy and protect cardiomyocytes by binding to inhibition of BMP4. In addition, Chrdl1 can inhibit the differentiation of cardiac fibroblasts into cardiomyofibroblasts by binding to inhibition of TGF-?1 cardiac fibroblasts, inhibiting cardiac fibrosis and pathological cardiac remodeling. Therefore, therapeutic strategies targeting Chrdl1 may be developed as a new approach for the treatment of myocardial infarction.

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