People tend to think about fat as bland and bad for you, but this couldn’t be further from the truth! Healthy fat is needed for energy storage, which fuels you throughout the day and protects your other organs from the harmful effects of fat storage. Fat also is a central player in energy balance and metabolism, signaling to other organs like the brain, muscle, and liver to regulate things like food intake. It’s only when fat becomes unhealthy that issues start to arise, like the development of metabolic diseases such as type 2 diabetes.

Using single nuclear RNA sequencing, we have identified multiple subpopulations of adipocytes, some of which are correlated with metabolic disease. The projects here aim to further explore how these populations arise, both to better understand fat biology and also to hopefully develop disease treatments.

One question that frequently comes up in the interpretation of single cell data is the question of cell type versus cell state—in other words, are the subclusters distinct because they have a separate developmental origin or are they transiently responding to some sort of signaling event causing a temporary change in gene expression. Because single cell experiments are capturing cells at a snapshot in time, it can be difficult to tell the difference between these possibilities using the single cell data alone. We now will take the next step in understanding the drivers of these populations by studying candidate transcription factors and cell surface receptors that may influence the differentiation of adipocytes into one subpopulation over another.

a. Unpublished sNuc-seq data of adipocytes from males and females, showing sex-specific expression of Y chromosome gene USP9Y, as well as sex-selective expression of autosome gene LRP1B. b. Subclustering of adipocytes from a published sNuc-seq dataset of breast tissue from transgender and cisgender individuals. c. Illustration of the four core genotypes model, in which sex chromosome and gonadal state are inherited separately. d. Weight curve of mice from the four core genotype model. e. Illustration of experiment comparing adipose tissue from transgender and cisgender individuals.

We know that men and women have different likelihoods of developing metabolic disease but ​the mechanisms behind this difference remain unclear. Our data has shown that adipocyte subpopulations can vary in men and women, and that the genes describing these differences are both autosomal and Y chromosome genes. To better elucidate the differences between adipocytes, we propose collecting fat samples in both mouse and human models that differentiate between sex chromosome and sex hormonal states and subjecting these samples to single nuclear RNA sequencing.

Mouse model: We have collected tissues from “four core genotypes” mice. In this model, the Sry gene has been taken off the Y chromosome and inserted onto an autosome, allowing the birth of XX and XY genotype mice independent of the development of testes or ovaries.

Human model: We plan to work with surgeons providing gender affirming care to collect discarded fat samples from transgender patients who are on hormonal therapy, and comparing these to age- and weight- matched cisgender patients.