# Car4 regulates M2 macrophage responses and host protection to helminths

> **NIH NIH R01** · RUTGERS BIOMEDICAL AND HEALTH SCIENCES · 2024 · $632,840

## Abstract

PROJECT SUMMARY. The prevalence of parasitic helminth infections is estimated at two billion individuals
infected worldwide. Many helminths migrate through the lung as part of their developmental cycles and as a
result promote substantial lung damage and tissue fibrosis. Our studies and those of others have shown that
alveolar macrophages (AMs) with an alternatively activated or M2 phenotype are critical regulators of these
responses. Alveolar macrophages are the most abundant immune cell in the parenchyma of the lung and play
diverse metabolic and immunoregulatory roles that are needed to maintain lung function. Despite their
importance, the molecular mechanisms that regulate AM activation and their M2 responses remain to be fully
defined. Gaining a better understanding of the factors that regulate AM activation could reveal novel
therapeutic targets to treat diverse forms of lung inflammation including fibrosis. Our new studies have
shown that the enzyme carbonic anhydrase 4 (Car4) is a lineage-identifying feature of AMs. Carbonic
anhydrases are a family of enzymes that are traditionally known for their ability to regulate pH and CO2
homeostasis. However, our published studies have recently identified that Car enzymes also play important
roles in regulating immune cell activation and antihelminth immunity. Therefore, we sought to investigate
whether Car4 regulates the phenotypes and functions of AMs. To test this, we generated a novel Car4-floxed
mouse to selectively delete Car4 in AMs. Importantly, mice with Car4-deficient AMs (Car4-AM-/- mice) exhibited
spontaneous induction of M2 and profibrotic pathways and presented with features of altered lipid metabolism
and increased hypoxia-inducible factor (HIF) signaling. To further investigate the role of Car4 in regulating the
M2 activation of AMs we infected Car4-AM-/- mice with Nippostrongylus brasiliensis (Nb), a parasitic infection
that promotes robust M2 responses and lung pathology. Importantly, Car4-AM-/- mice infected with Nb exhibited
dramatically elevated M2 responses, increased lung fibrosis and suffered from significantly reduced oxygen
levels. Collectively, these data provoke the hypothesis that Car4 regulates the metabolism of AMs in a manner
that restricts M2 activation and tissue fibrosis. This hypothesis will be tested in the three Aims. Aim 1 will focus
on the importance of HIF-associated pathways in regulating the bioenergetic state of AMs and their
M2/profibrotic phenotype. Aim 2 will investigate the role Car4 plays in regulating M2 activation and pulmonary
fibrosis in the context of helminth-induce inflammation. Aim 3, will investigate whether Car4 also instructs the
activation of newly seeded monocyte-derived alveolar macrophages that populate the lung post-Nb infection
and acquire an M2 phenotype. Gaining better insight into these pathways may lead to the development of new
therapeutic strategies to treat lung disease and tissue fibrosis.

## Key facts

- **NIH application ID:** 10999649
- **Project number:** 1R01AI180644-01A1
- **Recipient organization:** RUTGERS BIOMEDICAL AND HEALTH SCIENCES
- **Principal Investigator:** Mark Christopher Siracusa
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $632,840
- **Award type:** 1
- **Project period:** 2024-06-07 → 2029-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10999649

## Citation

> US National Institutes of Health, RePORTER application 10999649, Car4 regulates M2 macrophage responses and host protection to helminths (1R01AI180644-01A1). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/10999649. Licensed CC0.

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