A viral vector carrying ALPK3 restored heart function in adult mice with inherited heart muscle disease
A viral vector carrying ALPK3 restored heart function in adult mice with inherited heart muscle disease
On 19 August, researchers reported in Nature Cardiovascular Research that they had developed a viral vector that delivers a complete, functional copy of the ALPK3 gene to heart cells. The disease was assessed in mice before treatment. After the vector was administered, heart function and structure returned to the levels seen in healthy animals. ALPK3 delivery also restored contractile force in two human cardiac organoid models, which are miniature tissue models made from human cells.
The heart contracts through sarcomeres, repeating protein structures within muscle cells. ALPK3 helps maintain sarcomere proteins in a functional state. When mice lack two functional copies of ALPK3, their hearts enlarge and pump blood less effectively. In humans, disease-causing variants of this gene cause inherited cardiomyopathies, which are diseases of the heart muscle. ALPK3 variants are associated with approximately 2% of hypertrophic cardiomyopathy cases.
In a 2023 study, the same group showed that ALPK3 is located at the M-band, the central region of the sarcomere, and is involved in removing damaged proteins. Loss of ALPK3 disrupted sarcomere organization and cell contraction. The researchers therefore tested whether a functional copy of the gene could restore organization to the contractile apparatus of a heart that was already diseased. To do this, they had to package a 5.8 thousand base-pair ALPK3 construct into AAV, a viral gene carrier, even though the usual capacity of AAV is about 4.7 thousand base pairs. Base pairs can be understood as the individual “letters” of DNA. The group shortened the construct’s regulatory regions and selected the TNNT2 promoter, a DNA sequence that activates the gene mainly in heart cells. The researchers detected both ends of the RNA, the gene’s working copy, as well as protein fragments spanning its entire length. This showed that the heart tissue was producing full-length ALPK3.
The therapy was first administered to newborn mice to test whether it could prevent the disease. The main experiment used six-week-old animals. Before receiving the vector, they had already been found to have weak heart contractions, enlargement of the left ventricle, and impaired relaxation. Eight mice received a control vector, while nine received ALPK3. They were monitored until 18 weeks of age. After treatment, cardiac ultrasound findings, heart mass, wall thickness, and tissue structure under the microscope matched those of healthy mice.
Large-scale protein analysis connected this result to the original hypothesis. Compared with healthy mice, diseased mice showed differences in 1 612 of the approximately 6 000 proteins detected. After ALPK3 delivery, only 81 proteins remained different. At the same time, the composition of the contractile filaments, heart structure, and heart function returned to normal.
The authors then tested whether ALPK3 could help when another gene in the same contractile apparatus was defective. TTN encodes titin, an enormous protein that forms the structural framework of the sarcomere. TTN variants that produce a shortened form of titin often cause dilated cardiomyopathy, in which the heart chambers become enlarged. The TTN gene substantially exceeds the capacity of AAV. In human cardiac organoids carrying these variants, the authors observed reduced ALPK3 levels. The ALPK3 vector restored contractile force to the level measured in organoids with the same genetic background but without the variant. This experiment tested whether restoring ALPK3 could partially correct a defect in the shared contractile apparatus in a human model of TTN cardiomyopathy.