# Biochemical and cellular mechanisms linking actin mutations to visceral myopathy

> **NIH NIH R01** · CHILDREN'S HOSP OF PHILADELPHIA · 2024 · $674,061

## Abstract

Project Summary: Our ultimate goal is to find new ways to improve smooth muscle function in people with
visceral myopathy, a disease defined by profound bowel, bladder and uterine smooth muscle dysfunction.
Bowel dysfunction, called myopathic Chronic Intestinal Pseudo-Obstruction (CIPO), is often treated by
intravenous nutrition. Bladder weakness often requires catheterization. When symptoms start in utero, colon
growth is minimal, causing Megacystis Microcolon Intestinal Hypoperistalsis Syndrome (MMIHS). Only ~20%
of people with MMIHS survive to adulthood. Current treatments may reduce symptoms but are not based on
disease mechanisms. Recent data show that 44% of people with MMIHS/CIPO have heterozygous point
mutations in gamma smooth muscle actin (ACTG2), one of 6 actin isoforms. Actin isoforms have distinct roles
in cells, and while actin is well studied, ACTG2 is barely studied. Myopathy-causing ACTG2 mutations are
spread throughout the actin structure. This suggests variant-specific disease mechanisms that could benefit
from variant-specific therapies. To design such therapies, we need a deep understanding of how individual
variants cause disease. We therefore pursue an integrated strategy, combining biochemical, structural, cellular
and stem cell approaches to determine how ACTG2 mutations cause visceral myopathy. Technical
breakthroughs and extensive preliminary data set the groundwork for success. In Aim 1, we develop new ways
to express recombinant human actin in human cells, without tags and featuring natural post-translational
modifications. This major innovation opens the way to biochemical studies of ACTG2, and should also facilitate
studies of variants of other actin isoforms causing skeletal myopathy, cardiomyopathy, vascular disease,
sensorineural hearing loss, and congenital malformations. Using recombinant ACTG2, we will study the
biochemical-structural properties of disease-causing ACTG2 variants, and their interactions with key Actin-
Binding Proteins (ABPs) that regulate actin assembly. To determine how mutations affect cell biology (Aim 2),
we express wild-type or mutant ACTG2 in human Intestinal Smooth Muscle Cells (hISMC). We selected
hISMC because disease-causing ACTG2 variants might alter interactions with ABPs or depend on cell-type
specific post-translational modifications. Our innovative quantitative image analysis pipeline already revealed
how the most common ACTG2 mutation (R257C) affects the actin cytoskeleton and cell biology. We will now
use this strategy to study other ACTG2 mutations. Some mutations might also cause myopathy by preventing
the MRTF-A transcription factor from entering the nucleus to induce contractile gene expression and smooth
muscle differentiation. To test this hypothesis, we invented a new way to convert human Pluripotent Stem Cells
(hPSCs) to visceral smooth muscle-like cells (Aim 3) and made cell lines expressing disease-causing ACTG2
variants. Our cross-disciplinary, integrated strategy s...

## Key facts

- **NIH application ID:** 10910114
- **Project number:** 5R01DK128282-04
- **Recipient organization:** CHILDREN'S HOSP OF PHILADELPHIA
- **Principal Investigator:** ROBERT O HEUCKEROTH
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $674,061
- **Award type:** 5
- **Project period:** 2021-09-28 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10910114

## Citation

> US National Institutes of Health, RePORTER application 10910114, Biochemical and cellular mechanisms linking actin mutations to visceral myopathy (5R01DK128282-04). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10910114. Licensed CC0.

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