Latent TGF? binding protein 4 (LTBP4) modifies muscular dystrophy in mice and in humans with Duchenne Muscular Dystrophy. LTBP4 is an extracellular matrix protein that binds latent TGF? to form the large latent complex. With stimulation like injury, LTBPs undergoes a conformational shift and proteolytic cleavage which releases latent TGF?, which is the first step in its activation. Activated TGF? has been implicated in fibrosis in many solid organs, and is a prominent feature of dystrophic muscle and injured muscle. Excessive TGF? is also known to inhibit muscle regeneration. In Duchenne Muscular Dystrophy, the protective LTBP4 variants that predict prolonged ambulation cause reduced TGF? signaling. Similarly, in mice the protective Ltbp4 allele is linked to reduced TGF? signaling. LTBP4 binds all three primary TGF? forms. Overexpression of the protective LTBP4 form in mouse muscle reduces fibrosis and also leads to increased muscle mass in the context of muscular dystrophy. LTBP4 not only binds TGF? but LTBP4 also binds myostatin. Domain mapping of LTBP4 binding sites demonstrated that TGF? and myostatin binding is mediated by distinct regions of LTBP4. LTBP4 therefore regulates multiple cytokines by sequestering these molecules in the matrix, rendering them inactive. A mechanism to reduce TGF? AND myostatin is an attractive target for treating muscular dystrophy since such an approach would reduce muscle fibrosis and promote muscle growth. This proposal outlines experiments designed to better define the mechanism by which LTBP4 acts.
The first aim i s designed to evaluate the relative contribution of TGF? and myostatin binding to LTBP4's effect.
The second aim will investigate how manipulating LTBP4 affects fibrosis and muscle recovery after injury and in muscular dystrophy.
The third aim will assess the importance of LTBP4's hinge region since this region mediates its effect as a modifier in muscular dystrophy.

Public Health Relevance

Muscular dystrophy is a disease where muscle is lost and replaced by fibrosis. We identified the LTBP4 gene and showed that it improves muscular dystrophy in mice and humans with Duchenne Muscular Dystrophy. We will define the mechanism by which LTBP4 improves muscular dystrophy and test an approach to manipulate LTBP4 to treat muscular dystrophy.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL140938-02
Application #
9674531
Study Section
Skeletal Muscle Biology and Exercise Physiology Study Section (SMEP)
Program Officer
Kaltman, Jonathan R
Project Start
2018-04-01
Project End
2022-01-31
Budget Start
2019-02-01
Budget End
2020-01-31
Support Year
2
Fiscal Year
2019
Total Cost
Indirect Cost
Name
Northwestern University at Chicago
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
005436803
City
Chicago
State
IL
Country
United States
Zip Code
60611