The obesity rate has more than doubled in the
last 30 years, affecting more than one billion people worldwide. This
prevalent condition is also linked to other metabolic disorders,
including type 2 diabetes, cardiovascular diseases, chronic kidney
disease, and cancers. Current treatment options include lifestyle
interventions, bariatric surgery, and GLP-1 drugs like Ozempic or
Wegovy, but many patients struggle to access or complete these
treatments or to maintain their weight loss afterwards.
Salk Institute scientists are
looking for a new treatment strategy in microproteins, an understudied
class of molecules found throughout the body that play roles in both
health and disease. In a new study, the researchers screened thousands
of fat cell genes using CRISPR gene editing to find dozens of genes that
likely code for microproteins -- one of which they confirmed -- that
regulate either fat cell proliferation or lipid accumulation.
The findings, published in Proceedings of the National Academy of Sciences on
August 7, 2025, identify new microproteins that could potentially ser
ve
as drug targets to treat obesity and other metabolic disorders. The
study also showcases the value of CRISPR screening in future
microprotein discovery.
"CRISPR screening is extremely effective at finding important factors
in obesity and metabolism that could become therapeutic targets," says
senior author Alan Saghatelian, a professor and holder of the Dr.
Frederik Paulsen Chair at Salk. "These new screening technologies are
allowing us to reveal a whole new level of biological regulation driven
by microproteins. The more we screen, the more disease-associated
microproteins we find, and the more potential targets we have for future
drug development."
Current obesity and metabolic disorder therapeutics
When our energy consumption exceeds our energy expenditure, fat cells
can grow in both size and number. Fat cells store the excess energy in
the form of fatty molecules called lipids. But while some excess storage
is manageable, too much can cause fat deposits to accumulate around the
body -- leading to whole-body inflammation and organ dysfunction.
Many factors regulate this complex energy storage system. The problem
is, how do we find them all, and how do we filter for factors that may
make good therapeutic candidates?
This has been a longstanding question for Salk scientists. In fact,
Salk Professor Ronald Evans has been working on it for decades. Evans is
an expert on PPAR gamma, a key regulator of fat cell development and a
potent target for treating diabetes. Several drugs have been developed
to target PPAR gamma to treat obesity, but they resulted in side effects
like weight gain and bone loss. An ideal PPAR gamma-based obesity
therapeutic has yet to hit the market.
When PPAR gamma drugs fell short,
GLP-1 drugs entered the scene. GLP-1 is a peptide small enough to be
considered a microprotein, and it serves as a blood sugar and appetite
regulator. But, like PPAR gamma, GLP-1 drugs have their own
shortcomings, such as muscle loss and nausea. Nonetheless, the
popularity of GLP-1 drugs demonstrates a promising future for
microprotein drugs in the obesity therapeutic space.
Saghatelian's team is now searching for the next microprotein
therapeutic with new genetic tools that bring microproteins out of the
"dark." For many years, long stretches of the genome have been
considered "junk" and thus left unexplored. But recent technological
advances have allowed scientists to look at these dark sections and find
a hidden world of microproteins -- in turn, expanding protein libraries
by 10 to 30 percent.
In particular, the Salk team is using innovative CRISPR screening to
scour the "dark" for possible microproteins. This approach is enabling
the simultaneous discovery of thousands of potential microproteins
involved in lipid storage and fat cell biology, accelerating the search
for the next PPAR gamma or GLP-1 drug.
How CRISPR screening accelerates the search for microproteins
CRISPR screens work by cutting out genes of interest in cells and
observing whether the cell thrives or dies without them. From these
results, scientists can determine the importance and function of
specific genes. In this case, the Salk team was interested in genes that
may code for microproteins involved in fat cell differentiation or
proliferation.
"We wanted to know if there was anything we had been missing in all
these years of research into the body's metabolic processes," says first
author Victor Pai, a postdoctoral researcher in Saghatelian's lab. "And
CRISPR allows us to pick out interesting and functional genes that
specifically impact lipid accumulation and fat cell development."
This latest research follows up on a
prior study from Saghatelian's lab. The previous study identified
thousands of potential microproteins by analyzing microprotein-coding
RNA strands derived from mouse fat tissues. These microprotein-coding
RNA strands were filed away to await investigation into their functions.
The new study first expanded this collection to include additional
microproteins identified from a pre-fat cell model. Notably, this new
model captures the differentiation process from pre-fat cell to a fully
mature fat cell. Next, the researchers screened the cell model with
CRISPR to determine how many of these potential microproteins were
involved in fat cell differentiation or proliferation.
"We're not the first to screen for microproteins with CRISPR," adds
Pai, "but we're the first to look for microproteins involved in fat cell
proliferation. This is a huge step for metabolism and obesity
research."
Microproteins of interest and next steps
Using their mouse model and CRISPR screening approach, the team
identified microproteins that may be involved in fat cell biology. They
then narrowed the pool even further with another experiment to create a
shortlist of 38 potential microproteins involved in lipid droplet
formation -- which indicates increasing fat storage -- during fat cell
differentiation.
At this point, the shortlisted microproteins were all still
"potential" microproteins. This is because the genetic screening finds
genes that may code for microproteins, rather than finding the
microproteins themselves. While this approach is a helpful workaround to
finding microproteins that are otherwise so small they elude capture,
it also means that the screened microproteins require further testing to
confirm whether they are functional.
And that's what the Salk team did next. They picked several of the
shortlisted microproteins to test and were able to verify one. Pai
hypothesizes this new microprotein, called Adipocyte-smORF-1183,
influences lipid droplet formation in fat cells (also known as
adipocytes).
Verification of Adipocyte-smORF-1183 is an exciting step toward
identifying more microproteins involved in lipid accumulation and fat
cell regulation in obesity. It also verifies that CRISPR is an effective
tool for finding microproteins involved in fat cell biology, obesity,
and metabolism.
"That's the goal of research,
right?" says Saghatelian. "You keep going. It's a constant process of
improvement as we establish better technology and better workflows to
enhance discovery and, eventually, therapeutic outcomes down the line."
Next, the researchers will repeat the study with human fat cells.
They also hope their success inspires others to use CRISPR screenings to
continue bringing microproteins out from the dark -- like
Adipocyte-smORF-1183, which until now, was considered an unimportant bit
of "junk" DNA.
Further validation or screening of new cell libraries will expand the
list of potential drug candidates, setting the stage for the
new-and-improved obesity and metabolic disorder therapeutics of the
future.
Other authors include Hazel Shan, Cynthia Donaldson, Joan Vaughan,
Eduardo V. De Souza, Carolyn O'Connor, and Michelle Liem of Salk; and
Antonio Pinto and Jolene Diedrich of Scripps Research Institute.
The work was supported by the National Institutes of Health (F32
DK132927, RC2 DK129961, R01 DK106210, R01 GM102491, RF1 AG086547, NCI
Cancer Center P30 014195, S10- OD023689, and S10-OD034268), Ferring
Foundation, Clayton Foundation, and Larry and Carol Greenfield
Technology Fund.
Journal Reference:
- Victor J. Pai, Huanqi Shan, Cynthia J. Donaldson, Joan M. Vaughan,
Eduardo V. De Souza, Carolyn O’Connor, Michelle Liem, Antonio F. M.
Pinto, Jolene Diedrich, Alan Saghatelian. CRISPR–Cas9 screening reveals microproteins regulating adipocyte proliferation and lipid metabolism. Proceedings of the National Academy of Sciences, 2025; 122 (32) DOI: 10.1073/pnas.2506534122
Courtesy:
Salk Institute. "Scientists just found a tiny molecule that could change
how we lose weight." ScienceDaily. ScienceDaily, 10 August 2025.
<www.sciencedaily.com/releases/2025/08/250809100924.htm>.
