# Mechanisms Underlying the Dominant Negative Phenotype in Hereditary Angioedema

> **NIH VA I01** · VA SAN DIEGO HEALTHCARE SYSTEM · 2020 · —

## Abstract

Hereditary angioedema (HAE) is an autosomal dominant disease caused by mutations in SERPING1. Almost
all HAE patients are heterozygotes, having one normal and one mutated copy of SERPING1 with the
concurrent expression of both mutant and wild-type C1 inhibitor (C1INH) proteins in the same cell. The
resulting haploinsufficiency would be expected to result in patients having 50% of the normal level of C1INH in
their plasma; however, HAE patients typically have plasma levels of functional C1INH that are between 10-
20% of normal. The mechanism responsible for this unexpectedly low level of functional C1INH has never
been understood and is the focus of this application. We have shown that mutant C1INH proteins interfere with
the secretion of wild-type (WT) C1INH protein. The overall hypothesis of this application is that mutant C1INH
exerts a dominant negative effect on wild-type C1INH, reducing the level of functional C1INH below the
threshold required for swelling and thus is responsible for the dominant negative phenotype of HAE.
The mechanisms of this dominant negative phenotype will be studied using both transfected cells expressing
wild-type and mutant C1INH as well as in HAE patient monocytes. Specific tagging of wild-type and mutant
C1INH proteins will be utilized to specifically follow trafficking and secretion of both C1INH proteins in
transfected cells. HAE and control monocytes will also be studied. Aim 1 will characterize the intracellular
trafficking and disposition of wild-type C1INH in cells expressing both wild-type and mutant C1INH proteins.
We will determine where these proteins are retained within the cell using confocal and immunoelectron
microscopy. We will then determine if wild-type C1INH forms oligomers with mutant C1INH using native gel
immunoblots and pull-down experiments with tagged proteins. Next we will assess evidence for activation of
autophagic flux in cells expressing WT plus mutant C1INH, and correlate autophagy with inhibition of WT
C1INH secretion. We will also analyze the impact ER stress pathways, including the unfolded protein response
and ER associated degradation, on the dominant negative effect. Aim 2 will then elucidate the biophysical
properties of C1INH that contribute to its susceptibility to intracellular retention when expressed with mutant
serpin proteins. We will create chimeric C1INH and a1-AT proteins though swapping of homologous structures
and define critical sequences required to manifest the dominant negative phenotype. We will also identify
proteins that interact with C1INH within the cell. Finally, we will use multivariate analyses to understand how
each of these parameters may contribute to the secretion of functional C1INH in HAE monocytes.
By the end of this project, it is anticipated that the dominant negative effect on wild-type C1INH secretion in
HAE will be clearly understood. This would set the stage for subsequent studies attempting to develop
therapeutic approaches that could abrog...

## Key facts

- **NIH application ID:** 9781540
- **Project number:** 1I01BX004240-01A1
- **Recipient organization:** VA SAN DIEGO HEALTHCARE SYSTEM
- **Principal Investigator:** Bruce L. Zuraw
- **Activity code:** I01 (R01, R21, SBIR, etc.)
- **Funding institute:** VA
- **Fiscal year:** 2020
- **Award amount:** —
- **Award type:** 1
- **Project period:** 2019-10-01 → 2023-09-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9781540

## Citation

> US National Institutes of Health, RePORTER application 9781540, Mechanisms Underlying the Dominant Negative Phenotype in Hereditary Angioedema (1I01BX004240-01A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9781540. Licensed CC0.

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