Regenerative Medicine: New Clue from Fish about Healing Spinal Cord Injuries

Zebrafish Spinal Cord

Caption: Tissue section of zebrafish spinal cord regenerating after injury. Glial cells (red) cross the gap between the severed ends first. Neuronal cells (green) soon follow. Cell nuclei are stained blue and purple.
Credit: Mayssa Mokalled and Kenneth Poss, Duke University, Durham, NC

Certain organisms have remarkable abilities to achieve self-healing, and a fascinating example is the zebrafish (Danio rerio), a species of tropical freshwater fish that’s an increasingly popular model organism for biological research. When the fish’s spinal cord is severed, something remarkable happens that doesn’t occur in humans: supportive cells in the nervous system bridge the gap, allowing new nerve tissue to restore the spinal cord to full function within weeks.

Pretty incredible, but how does this occur? NIH-funded researchers have just found an important clue. They’ve discovered that the zebrafish’s damaged cells secrete a molecule known as connective tissue growth factor a (CTGFa) that is essential in regenerating its severed spinal cord. What’s particularly encouraging to those looking for ways to help the 12,000 Americans who suffer spinal cord injuries each year is that humans also produce a form of CTGF. In fact, the researchers found that applying human CTGF near the injured site even accelerated the regenerative process in zebrafish. While this growth factor by itself is unlikely to produce significant spinal cord regeneration in human patients, the findings do offer a promising lead for researchers pursuing the next generation of regenerative therapies.

Continue reading

Cool Videos: Regenerating Nerve Fibers

If you enjoy action movies, you can probably think of a superhero—maybe Wolverine?—who can lose a limb in battle, yet grow it right back and keep on going. But could regenerating a lost limb ever happen in real life? Some scientists are working hard to understand how other organisms do this.

As shown in this video of a regenerating fish fin, biology can sometimes be stranger than fiction. The zebrafish (Danio rerio), which is a species of tropical freshwater fish that’s an increasingly popular model organism for biological research, is among the few vertebrates that can regrow body parts after they’ve been badly damaged or even lost. Using time-lapse photography over a period of about 12 hours, NIH grantee Sandra Rieger, now at MDI Biological Laboratory, Bar Harbor, ME, used a fluorescent marker (green) to track a nerve fiber spreading through the skin of a zebrafish tail fin (gray). The nerve regeneration was occurring in tissue being spontaneously formed to replace a section of a young zebrafish’s tail fin that had been lopped off 3 days earlier.

Along with other tools, Rieger is using such imaging to explore how the processes of nerve regeneration and wound healing are coordinated. The researcher started out by using a laser to sever nerves in a zebrafish’s original tail fin, assuming that the nerves would regenerate—but they did not! So, she went back to the drawing board and discovered that if she also used the laser to damage some skin cells in the tail fin, the nerves regenerated. Rieger suspects the answer to the differing outcomes lies in the fact that the fish’s damaged skin cells release hydrogen peroxide, which may serve as a critical prompt for the regenerative process [1]. Rieger and colleagues went on discover that the opposite is also true: when they used a cancer chemotherapy drug to damage skin cells in a zebrafish tail fin, it contributed to the degeneration of the fin’s nerve fibers [2].

Based on these findings, Rieger wants to see whether similar processes may be going on in the hands and feet of cancer patients who struggle with painful nerve damage, called peripheral neuropathy, caused by certain chemotherapy drugs, including taxanes and platinum compounds. For some people, the pain and tingling can be so severe that doctors must postpone or even halt cancer treatment. Rieger is currently working with a collaborator to see if two protective molecules found in the zebrafish might be used to reduce or prevent chemotherapy-induced peripheral neuropathy in humans.

In recent years, a great deal of regenerative medicine has focused on learning to use stem cell technologies to make different kinds of replacement tissue. Still, as Rieger’s work demonstrates, there remains much to be gained from studying model organisms, such as the zebrafish and axolotl salamander, that possess the natural ability to regenerate limbs, tissues, and even internal organs. Now, that’s a super power we’d all like to have.

Reference:

[1] Hydrogen peroxide promotes injury-induced peripheral sensory axon regeneration in the zebrafish skin. Rieger S, Sagasti A. PLoS Biol. 2011 May;9(5):e1000621

[2] Paclitaxel-induced epithelial damage and ectopic MMP-13 expression promotes neurotoxicity in zebrafish. Lisse TS, Middleton LJ, Pellegrini AD, Martin PB, Spaulding EL, Lopes O, Brochu EA, Carter EV, Waldron A, Rieger S. Proc Natl Acad Sci U S A. 2016 Apr 12;113(15):E2189-E2198.

Links:

Chemotherapy-Induced Peripheral Neuropathy (National Cancer Institute/NIH)

Learning About Human Biology From a Fish (National Institute of General Medical Sciences/NIH)

Sandra Rieger (MDI Biological Laboratory, Bar Harbor, ME)

NIH Support: National Institute of Dental and Craniofacial Research; National Institute of General Medical Sciences; National Institute of Neurological Disorders and Stroke

Scoliosis Traced to Problems in Spinal Fluid Flow

Zebra fish model for scoliosis study

Caption: Normal zebrafish (top left) and a normal skeleton (bottom left); zebrafish with scoliosis (top right) and an abnormal scoliotic skeleton (bottom right).
Credit: Grimes DT, Boswell CW, Morante NF, Henkelman RM.

Many of us may remember undergoing a simple screening test in school to look for abnormal curvatures of the spine. The condition known as adolescent idiopathic scoliosis (IS) affects 3 percent of children, typically showing up in the tween or early teen years when kids are growing rapidly. While scoliosis can occur due to physical defects in bones or muscles, more often the C- or S-shaped spinal curves develop for unknown reasons. Because the basic biological mechanisms of IS have been poorly understood, treatment to prevent further progression and potentially painful disfigurement has been limited to restrictive braces or corrective surgery.

Now, in work involving zebrafish models of IS, a team of NIH-funded researchers and their colleagues report a surprising discovery that suggests it may be possible to develop more precisely targeted therapeutics to reduce or even prevent scoliosis. The team’s experiments have, for the first time, shown that mutation of a gene associated with spinal curvature in both zebrafish and humans has its effect by altering the function of the tiny hair-like projections, known as cilia, that line the spinal cord. Without the cilia’s normal, beating movements, the fluid that bathes the brain and spinal cord doesn’t flow properly, and zebrafish develop abnormal spinal curves that look much like those seen in kids with scoliosis. However, when the researchers used genetic engineering to correct such mutations and thereby restore normal cilia function and flow of cerebral spinal fluid (CSF), the zebrafish did not develop spinal curvature.

Continue reading

Snapshots of Life: Arabidopsis Art

Arabidopsis

Credit: Nathanaël Prunet, California Institute of Technology, Pasadena

Modern sculptors might want to take a few notes from Mother Nature. The striking, stone-like forms that you see above are a micrograph of flower buds from the mustard plant Arabidopsis thaliana, which serves as an important model organism in biomedical research. In the center are the shoot apical meristems, consisting of undifferentiated stem cells (gray) that give rise to the flowers. Around the edge are buds that are several hours older, in which the flowers have just begun to form off of the shoot apical meristems. And, to the bottom left, are four structures that are the early sepals that will surround the fully formed flower that will bloom in a few weeks. The colored circles indicate areas of gene activity involved in determining the gender of the resulting flower, with masculinizing genes marked in green and feminizing in red.

This image, a winner in the Federation of American Societies for Experimental Biology’s 2015 BioArt competition, is the creation of postdoctoral student Nathanaёl Prunet, now in the NIH-supported lab of Elliot Meyerowitz at the California Institute of Technology, Pasadena, CA. Using scanning electron microscopy, Prunet snapped multiple 2D photographs of Arabidopsis buds at different tissue depths and computationally combined them to produce this 3D image.

Continue reading

Snapshots of Life: From Arabidopsis to Zinc

heat map of zZinc levels in an Arabidopsis thaliana plant leaf

Credit: Suzana Car, Maria Hindt, Tracy Punshon, and Mary Lou Guerinot, Dartmouth College, Hanover, NH

To most people, the plant Arabidopsis thaliana might seem like just another pesky weed. But for plant biologists, this member of the mustard green family is a valuable model for studying a wide array of biological processes—including the patterns of zinc acquisition shown so vividly in the Arabidopsis leaf above. Using synchrotron X-ray fluorescence technology, researchers found zinc concentrations varied considerably even within a single leaf; the lowest levels are marked in blue, next lowest in green, medium in red, and highest in white, concentrated at the base of tiny hairs (trichomes) that extend from the leaf’s surface.

A winner in the Federation of American Societies for Experimental Biology’s 2015 BioArt competition, this micrograph stems from work being conducted by Suzana Car and colleagues in the NIH-funded lab of Mary Lou Guerinot at Dartmouth College, Hanover, NH. The researchers are still trying to figure out exactly what zinc is doing at the various locations within Arabidopsis, as well as whether zinc concentrations are constant or variable. What is well known is that zinc is an essential micronutrient for human health, with more than 300 enzymes dependent on this mineral to catalyze chemical reactions within our bodies.

Continue reading