December 17, 2019 | David F. Coppedge

Watch the Christmas Lights in Your Muscles

Scientists use fluorescent tags to shine light on the biggest proteins in the human body.

The caption of a photo in Medical Xpress is boring, but the photo itself is ready for Christmas! It’s a microphoto of the giant protein titin—largest protein in the human body—lit up in Christmas lights. Titin is essential to our muscles. The caption reads, “Remodelling of cardiomyocytes includes sarcomere assembly and growth (red and green stripes, 12 hours).” OK, now the plain English: cardiomycetes are heart cells. Sarcomeres are muscle structures containing titin. The cells come together (“remodelling”) in a programmed way to form sarcomeres, which make up our muscle fibers. But how did they get such a Christmasy picture at Max Delbrück Center for Molecular Medicine?

As twinkling lights brighten the holiday season, Max Delbrueck Center for Molecular Medicine researchers are cheered by red and green lights for an entirely different reason. Using colorful probes, a team has tracked the full lifecycle of titin, the body’s largest protein known to play a key role in muscle tissue. Observing titin from synthesis to degradation has provided novel insight into the formation of sarcomeres, the main contractile units of heart and skeletal muscle. The results were reported in the journal Proceedings of the National Academy of Sciences (PNAS).

Collage made from single cells expressing treen and red fluorescent titin proteins. Credit: Gotthardt Lab, MDC

The Christmas lights are added on for effect, just like people place lights on Christmas trees. But the structure itself, with its regular patterns looking like limbs on a Christmas fir tree, is very real. And when the lights go on, the tree itself becomes an object of beauty, just like the Christmas tree was beautiful in the forest.

Cardiomyocytes are highly specialized and cannot skip a beat,” said Michael Gotthardt, who heads MDC’s Neuromuscular and Cardiovascular Cell Biology Lab and spearheaded the research. “We can watch how titin is made and inserted into the myofilament while everything is still working. It’s beautiful to see.

The scientists at MDC were surprised to find that titin is much more dynamic than earlier believed. It’s not just an idle scaffold. It moves in a choreographed dance. Everything in the insertion is coordinated carefully so that the heart never skips a beat. Imagine trying to do heart surgery in situ on a beating heart!

The red and green fluorescent lights are attached to titin proteins

Heart muscle cells appear to have a pool of soluble titin spread throughout the sarcomere, ready to replace proteins damaged in the repetitive process of muscle expansion and contraction. Overextended proteins are moved out of the cells and then degraded. All of this happens over the course of a few hours, which sounds fast, but is actually much longer than for any other sarcomeric protein.

Individual sarcomeres are organized into muscle fibers.

Ribosomes are ready near the site to transcribe mRNA into titin as needed. The proteins are kept in a compartment ready for assembly, then are moved into position as needed. Spent proteins are removed in an organized manner.

The body has about 700 named skeletal muscles, not counting smooth muscles and cardiac muscles.

As we work our muscles, many coordinated steps are taking place at the cellular level beyond our normal experience. Scientists are just peering now into the secrets that people have been relying on for every finger, arm, leg movement and heartbeat since the dawn of creation.

That’s a Christmas present to delight in more than anything you could find under the tree. Many live for 60, 70, 80, 90 or 100 years with these systems operating reliably without fail. “And they run on potatoes!” Dr A. E. Wilder-Smith would exclaim.

Children should enjoy the great outdoors

These girls have no idea what wonders are going on inside their muscles.

According to the Bible’s account of the pre-Flood generations, these systems worked in Methuselah for almost a millennium (989 years). Every moment of every day and night, Methuselah’s heart never skipped a beat. The performance of God’s creations vastly exceed the capabilities of the world’s greatest inventors. Should we not give thanks for these gifts?


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