# Title:  Ventilator-induced diaphragm dysfunction: role of calpain signaling

> **NIH NIH R21** · UNIVERSITY OF FLORIDA · 2020 · $167,750

## Abstract

BACKGROUND: Mechanical ventilation (MV) is used to provide respiratory support to >15 million patients
annually during both critical illnesses and surgery. Although MV is often a life-saving intervention, prolonged MV
(≥12 hours) promotes problems in “weaning” patients from the ventilator; this failure to wean significantly
increases patient morbidity and mortality. While the cause of difficult weaning can be multifactorial, weak
inspiratory muscles (i.e., diaphragm) are a major factor. Indeed, an unintended consequence of ventilator support
is that prolonged MV results in diaphragmatic inactivity and the rapid development of diaphragm atrophy and
contractile dysfunction (collectively known as ventilator-induced diaphragm dysfunction (VIDD)). VIDD occurs
due to both decreased protein synthesis and increased protein breakdown in the diaphragm; however, the
upstream regulators that control these events remain unclear. Our compelling preliminary data suggest that the
cysteine protease calpain plays an essential signaling role in the development of VIDD. Indeed, our pilot
experiments reveal that prevention of calpain activation in the diaphragm protects against VIDD, indicating that
calpain is required for the development of VIDD. Importantly, these results challenge the current dogma that the
role of the classical calpains (i.e., calpain 1 and 2) in skeletal muscle atrophy is limited to cleavage of cytoskeletal
proteins. The mechanisms by which active calpain promotes VIDD remain unknown and are the focus of this
R21 application. HYPOTHESIS: Guided by our preliminary experiments, we hypothesize that active calpain is
an essential upstream regulator of both protein synthesis and proteolysis in diaphragm muscle during prolonged
MV. SPECIFIC AIMS: Aim 1 will determine if active calpain plays an essential role in MV-induced decreases in
anabolic signaling (i.e., Akt/mTOR) and protein synthesis in the diaphragm during prolonged MV. Aim 2 will
establish whether active calpain regulates MV-induced proteolysis in the diaphragm via activation of caspase-3
and forkhead box O (FoxO) transcription factors. APPROACH: We will test our hypothesis by utilizing a well-
established animal model of MV along with innovative molecular tools to prevent MV-induced calpain activation
in the diaphragm. Cause and effect will be determined using an adeno-associated virus vector (AAV9) to
overexpress a calpastatin transgene in the diaphragm that will prevent MV-induced activation of calpain. Primary
dependent measures include key steps in anabolic and proteolytic signaling, in vivo protein synthesis, rate of
diaphragm proteolysis, and assessment of both caspase-3 activity along with the transcriptional activity of FoxO
in the diaphragm. RELEVANCE: VIDD is a serious clinical problem because inspiratory muscle weakness is a
major cause of the inability to wean patients from the ventilator. Unfortunately, no standard clinical therapy exists
to prevent VIDD. These exciting explora...

## Key facts

- **NIH application ID:** 9889038
- **Project number:** 5R21AR073956-02
- **Recipient organization:** UNIVERSITY OF FLORIDA
- **Principal Investigator:** Scott K. Powers
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $167,750
- **Award type:** 5
- **Project period:** 2019-03-07 → 2021-05-16

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9889038

## Citation

> US National Institutes of Health, RePORTER application 9889038, Title:  Ventilator-induced diaphragm dysfunction: role of calpain signaling (5R21AR073956-02). Retrieved via AI Analytics 2026-06-08 from https://api.ai-analytics.org/grant/nih/9889038. Licensed CC0.

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