(Newswise)–In what they consider a surprise finding, Johns Hopkins Medicine researchers have demonstrated a key role for male sex hormone “signaling” in inducing—rather than suppressing—allergic lung inflammation in a mouse model of asthma.
The new study, they say, underscores the importance of appreciating sex differences and the role of sex hormones in the diagnosis and treatment of disease, and stresses the value of a personalized and precision medicine approach to clinical care for asthma specifically.
The mouse study, described Oct. 10 online in the Journal of Immunology, shows that in response to the experimental allergen ovalbumin, the main protein found in egg whites, chemical signaling produced by the primary male sex hormone testosterone acting through its receptor promoted lung inflammation in male mice.
“We have long known that asthma is more prevalent in pre-adolescent boys than in same-age girls, and that at puberty, when specific sex hormones increase, this switches, so that more teenage and adult women suffer from asthma than teenage and adult men,” says Nicola Heller, Ph.D., associate professor in the Department of Anesthesiology and Critical Care Medicine at the Johns Hopkins University School of Medicine. “This obviously suggests that sex hormones and changes in sex hormones play a role in the pathogenesis of asthma, so a better understanding of precisely how sex hormones change the immune system’s response to allergens has the potential to help us tailor asthma therapy more specifically to the sex of each patient.”
In a previous mouse study, Heller and her team demonstrated that the primary female sex hormone, estrogen, was a potent activator of a key cell type in the lungs and processes known to drive lung inflammation. Since post-adolescent and adult women are disproportionately affected by asthma compared to men, and estrogen levels far outstrip testosterone in post-pubescent females, it stood to reason that the male hormone, testosterone, might have a suppressing effect. Previous studies indeed suggested that testosterone conferred protective effects against allergic asthma in male mice. Male sex hormones also have been used as experimental therapy in asthmatic women.
For their new study, designed to better understand what they believed to be the protective effect of male sex hormones, the researchers used castrated male mice to precisely control and assess the role of these hormones in allergic asthma response. The researchers implanted pellets that release hormones at near normal levels for mice (about 1.42 nanograms per milliliterin pellet-treated castrated mice compared to 1.51 nanograms per milliliter in intact mice).
Also, because mice do not naturally develop allergic asthma, the researchers used a widely accepted model of the disorder created by injecting the animals with ovalbumin. When the animals subsequently inhaled aerosolized ovalbumin, they developed inflammation of the lung and other symptoms that mimic allergic asthma responses in people.
Lung inflammation is driven by the activation of specialized immune cells called alveolar macrophages—a cellular cleanup system. These macrophages also active participants in promoting inflammation, which is characterized by a kind of realignment of macrophage function known as polarization. The polarization process that occurs in the allergic lung, known as M2 polarization, has long been known to promote the production and secretion of inflammatory molecules that include chemokines and cytokines. These molecules then recruit other white blood cells, such as eosinophils, into the lungs and result in the typical markers of allergic asthma, including constriction of airways and lung tissue damage—or more well-known symptoms such as difficulty breathing and increased mucus production.
For the experiment, the researchers initially expected the lungs in the mice with implanted hormone pellets to exhibit a global reduction in lung inflammation and a natural macrophage state. The researchers indeed saw less inflammation, however, on further examination, they observed that the alveolar macrophages polarized to the M2 activated state, which indicates an inflammatory lung response. So, while male sex hormones appeared to suppress some aspects of the inflammatory response, they also appeared to trigger that response specifically in the macrophages.
This result “turned our original hypothesis on its head,” says Heller.
To then sort out if male sex hormones drove rather than suppressed inflammation in macrophages, the researchers created a genetically engineered mouse in which the so-called androgen receptors for testosterone were missing only in its macrophages. Therefore, even in the presence of natural male hormone signaling, the mouse macrophages could not respond to the hormone.
Using this mouse line, they again had the mice inhale the ovalbumin allergen to see if they could still induce lung inflammation via the macrophage polarization and activation route. The researchers saw reduced lung inflammation in the absence of male hormone receptors in response to the allergen in the male but not the female mice. This suggested that testosterone acting through the receptor was a driver of inflammation.
This lowered inflammation was accompanied by decreased M2 polarization of alveolar macrophages as well as decreased chemokine and cytokine production. For example, levels of chemokine CCL24—a signaling protein known to recruit eosinophils—decreased by 81 percent in knockout mice exposed to ovalbumin. Thus, there was a lack of eosinophil recruitment and an inhibition of lung inflammation. Importantly, this only occurred in male mice.
Overall, the researchers say, the experiments suggest that different inflammatory pathways can lead to the same disease processes, depending on factors such as sex or age. Mice are commonly used as models of allergic lung inflammation, but not all findings in mice translate to humans. If the mouse findings are determined to be applicable in humans, different people may have the same symptoms but need entirely different treatment options. Currently, inhaled steroids and antihistamines are the most common treatment options for both sexes. However, more specific treatments based on regulating the action of the male hormone receptor could be beneficial for male patients with uncontrolled asthma.
The researchers caution that this is a preliminary study done with an asthma-induced mouse model and an allergen not commonly seen in humans. Future studies using human allergens, such as dust mites or mold, in mice as well as tests with human subjects will further elucidate if hormone signaling plays a similar role in human asthma.
“Overall, our study affirms the need for physicians to really pay attention to where in their lifespan their patients are and to think about the role of sex hormones as augmenters of disease,” says Heller.
According to the National Institute of Allergy and Infectious Diseases, an estimated 26 million Americans are living with asthma. Each year, asthma-related complications result in nearly 1.3 million emergency room visits, account for about 14.2 million lost workdays and cost an average of 56 billion dollars.
This work was driven by Mireya Becerra-Díaz in Nicola Heller’s lab. Other Johns Hopkins researchers involved in this study include Aleksander Keselman and Ashley Strickland.
The study was funded by the National Institutes of Health under grant number R01 HL124477.