會跳動的幹細胞 “心臟補丁” (16 cm2) 成功修復老鼠心臟

新型人造肌肉有望給心臟打"補丁"2017-12-03來源：新華網新華社北京12月3日電 美國杜克大學研究人員新開發出一種能給心臟打"補丁"的人造肌肉。這種肌肉的強壯程度和電傳導性很接近健康成人心肌，而且其尺寸足以修復心臟常見損傷。研究人員利用多能幹細胞培育心臟"補丁"，這種幹細胞可以分化成身體中任何種類的細胞，包括心肌細胞和負責為心臟組織提供結構框架的成纖維細胞等。研究人員將這些細胞按特定比例置于凝膠狀物質中，使它們自我組織和生長。雖然培養心肌細胞早已不是新鮮事，但隨著培養尺寸增大，組織性能難以保證，因此早期人造心肌面積很小。通過反復實驗，研究人員找到了恰到好處的細胞配比和培養條件，成功培育出16平方厘米大、有一定厚度的大號"補丁"。動物實驗表明，這些"補丁"植入心臟後能繼續存活，並且運作良好。但為了實現修復人類壞死心肌的目標，研究人員還需讓心臟"補丁"變得更厚，並與原生肌肉完全融合。據介紹，給心臟打"補丁"能夠有效預防心臟衰竭及其並發症。"補丁"被植入壞死心肌後，能長時間保持活躍，為心臟收縮供能，順暢傳導電信號，還能分泌酶和生長因子，幫助修復受損組織。這項研究成果刊登在新一期英國《自然·通訊》網絡版上。

Beating Heart Patch is Large Enough to Repair the Human Heart  NOVEMBER 28, 2017   Beating patch is as strong and electrically active as healthy adult heart  By Ken Kingery  Biomedical engineers at Duke University have created a fully functioning artificial human heart muscle large enough to patch over damage typically seen in patients who have suffered a heart attack. The advance takes a major step toward the end goal of repairing dead heart muscle in human patients. The study appears online in Nature Communications on November 28, 2017. "Right now, virtually all existing therapies are aimed at reducing the symptoms from the damage that's already been done to the heart, but no approaches have been able to replace the muscle that's lost, because once it's dead, it does not grow back on its own," said Ilia Shadrin, a biomedical engineering doctoral student at Duke University and first author on the study. "This is a way that we could replace lost muscle with tissue made outside the body." Unlike some human organs, the heart cannot regenerate itself after a heart attack. The dead muscle is often replaced by scar tissue that can no longer transmit electrical signals or contract, both of which are necessary for smooth and forceful heartbeats. The end result is a disease commonly referred to as heart failure that affects over 12 million patients worldwide. New therapies, such as the one being developed by Shadrin and his advisor Nenad Bursac, professor of biomedical engineering at Duke, are needed to prevent heart failure and its lethal complications. Current clinical trials are testing the tactic of injecting stem cells derived from bone marrow, blood or the heart itself directly into the affected site in an attempt to replenish some of the damaged muscle. While there do seem to be some positive effects from these treatments, their mechanisms are not fully understood. Fewer than one percent of the injected cells survive and remain in the heart, and even fewer become cardiac muscle cells. Heart patches, on the other hand, could conceivably be implanted over the dead muscle and remain active for a long time, providing more strength for contractions and a smooth path for the heart's electrical signals to travel through. These patches also secrete enzymes and growth factors that could help recovery of damaged tissue that hasn't yet died. For this approach to work, however, a heart patch must be large enough to cover the affected tissue. It must also be just as strong and electrically active as the native heart tissue, or else the discrepancy could cause deadly arrhythmias. This is the first human heart patch to meet both criteria. "Creating individual cardiac muscle cells is pretty commonplace, but people have been focused on growing miniature tissues for drug development," said Bursac. "Scaling it up to this size is something that has never been done and it required a lot of engineering ingenuity." The cells for the heart patch are grown from human pluripotent stem cells -- the cells that can become any type of cell in the body. Bursac and Shadrin have successfully made patches using many different lines of human stem cells, including those derived from embryos and those artificially forced or "induced" into their pluripotent state. Various types of heart cells can be grown from these stem cells: cardiomyocytes, the cells responsible for muscle contraction; fibroblasts, the cells that provide structural framework for heart tissue; and endothelial and smooth muscle cells, the cells that form blood vessels. The researchers place these cells at specific ratios into a jelly-like substance where they self-organize and grow into functioning tissue. Finding the right combination of cells, support structures, growth factors, nutrients and culture conditions to grow large, fully functional patches of human heart tissue has taken the team years of work. Every container and procedure had to be sized up and engineered from scratch. And the key that brought it all together was a little bit of rocking and swaying. "It turns out that rocking the samples to bathe and splash them to improve nutrient delivery is extremely important," said Shadrin. "We obtained three-to-five times better results with the rocking cultures compared to our static samples." The results improved on the researchers' previous patches, which were one square centimeter and four square centimeters. They successfully scaled up to 16 square centimeters and five to eight cells thick. Tests show that the heart muscle in the patch is fully functional, with electrical, mechanical and structural properties that resemble those of a normal, healthy adult heart. "This is extremely difficult to do, as the larger the tissue that is grown, the harder it is to maintain the same properties throughout it," said Bursac. "Equally challenging has been making the tissues mature to adult strength on a fast timescale of five weeks while achieving properties that typically take years of normal human development." Bursac and Shadrin have already shown that these cardiac patches survive, become vascularized and maintain their function when implanted onto mouse and rat hearts. For a heart patch to ever actually replace the work of dead cardiac muscle in human patients, however, it would need to be much thicker than the tissue grown in this study. And for patches to be grown that thick, they need to be vascularized so that cells on the interior can receive enough oxygen and nutrients. Even then, researchers would have to figure out how to fully integrate the heart patch with the existing muscle. "Full integration like that is really important, not just to improve the heart's mechanical pumping, but to ensure the smooth spread of electrical waves and minimize the risk of arrhythmias," said Shadrin. "We are actively working on that, as are others, but for now, we are thrilled to have the 'size matters' part figured out," added Bursac. The research is part of a seven-year, $8.6 million grant from the National Institutes of Health. With the large heart patches in hand, the Bursac team is collaborating with researchers at the University of Alabama at Birmingham to develop procedures to successfully integrate the patch onto the hearts of pigs. Another affiliated team of researchers at the University of Wisconsin-Madison is working to develop improved stem cells for creating the main cell types that compose these heart patches, in the hopes of minimizing an immune response to the delivery of the engineered tissues. This research was supported by Foundation Leducq and the National Institutes of Health (R01HL104326, R01HL12652, UG3TR002142, U01HL134764, 5T32GM007171, F30HL122079).

CITATION: "Cardiopatch platform enables maturation and scale-up of human pluripotent stem cell-derived engineered heart tissues," Ilya Y. Shadrin, Brian W. Allen, Ying Qian, Christopher P. Jackman, Aaron L. Carlson, Mark E. Juhas, and Nenad Bursac. Nature Communications,  2017. DOI: 10.1038/s41467-017-01946-x