Researchers map how a single protein builds the calorie-burning infrastructure inside brown fat

Overview

Updated May 30

Every obesity drug on the market works by suppressing appetite — making people eat less. A team led by NYU researcher Farnaz Shamsi has mapped a completely different route: the protein SLIT3. An enzyme slices SLIT3 in two, and each half independently builds the blood vessels and nerve wiring that brown fat needs to burn calories as heat. The discovery, published in Nature Communications and validated in tissue from more than 1,500 people, identifies multiple molecular targets that could be turned into drugs.

Brown fat has tantalized obesity researchers since its rediscovery in adults in 2009. Yet every attempt to harness it therapeutically has stalled — the tissue is scarce in adults, and drugs that activate it in mice have failed in humans. This study shifts the approach from trying to switch brown fat on to upgrading the infrastructure that lets it function. If the pathway holds up in clinical development, it could become the first obesity treatment that increases energy expenditure rather than restricting energy intake. It could complement the GLP-1 drugs that have transformed the field.

Why it matters

If brown fat can be made to burn more calories, obesity treatment gains an entirely new mechanism beyond appetite suppression.

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Key Indicators

1,500+

Human tissue samples analyzed

Researchers validated the pathway in fat tissue from over 1,500 individuals, including people with obesity.

Druggable molecular targets identified

SLIT3 itself, its two fragments (N-terminal and C-terminal), the BMP1 enzyme, and the PLXNA1 receptor.

~$100B

GLP-1 obesity drug market (2025)

The current appetite-suppression market that an energy-expenditure approach could complement or compete with.

Approved brown-fat-activating obesity drugs

Despite 17 years of research since brown fat's rediscovery in adults, no drug targeting this mechanism has reached market.

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People Involved

Farnaz Shamsi

Senior author; Assistant Professor of Molecular Pathobiology, NYU College of Dentistry

Leading SLIT3/brown fat research program at NYU

Paul Cohen

Co-author; Physician-scientist at The Rockefeller University

Active collaborator on SLIT3 research

Organizations Involved

NYU College of Dentistry

Academic Research Institution

Home institution of senior author and primary research team

NYU's dental college houses the molecular pathobiology department where Shamsi's lab conducts brown fat metabolism research.

Nature Communications

Scientific Journal

Published the peer-reviewed SLIT3 study

A high-impact open-access journal in the Nature portfolio that publishes research across the natural sciences.

Timeline

April 2009 March 2026

6 events Latest: March 28th, 2026 · 5 months ago

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March 2026
Nature Communications publishes SLIT3 brown fat pathway discovery
Latest Publication

The peer-reviewed study reveals that the protein SLIT3 is cleaved by the enzyme BMP1 into two fragments — one that builds blood vessel networks and another that builds nerve networks in brown fat — with validation in tissue from over 1,500 people. Multiple druggable targets are identified.
March 28th, 2026
September 2024
Shamsi lab posts SLIT3 preprint on bioRxiv
Research

The NYU team posted preliminary findings on the SLIT3 pathway in brown fat as a preprint, beginning peer review.
September 24th, 2024
January 2021
52,000-patient study links brown fat to protection against chronic disease
Research

Paul Cohen's team at Rockefeller University analyzed 130,000 PET scans and found that obese people with detectable brown fat had diabetes and heart disease rates comparable to non-obese people — the strongest human evidence yet that brown fat matters clinically.
January 1st, 2021
January 2020
Chronic mirabegron improves metabolism but fails to produce weight loss
Clinical trial

Studies showed mirabegron improved brown fat activity, HDL cholesterol, and insulin sensitivity in obese patients, but produced no significant weight loss — a blow to the beta-3 agonist approach.
January 1st, 2020
January 2015
Mirabegron shown to activate human brown fat, but with side effects
Clinical trial

Aaron Cypess and colleagues at the National Institutes of Health demonstrated that mirabegron, a bladder drug, activated brown fat in humans. However, the effective dose was four times the approved amount and raised heart rate and blood pressure.
January 1st, 2015
April 2009
Three landmark papers prove adults have active brown fat
Discovery

The New England Journal of Medicine published three papers by Cypess, Virtanen, and van Marken Lichtenbelt using PET-CT scans to demonstrate that functional brown adipose tissue exists in adult humans — overturning decades of assumption that it disappeared after infancy.
April 9th, 2009

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

1987-2021

GLP-1 receptor agonist development (1987-2021)

Jens Juul Holst at the University of Copenhagen characterized glucagon-like peptide-1's role in insulin secretion in 1987. The first GLP-1 drug, exenatide (derived from Gila monster venom), reached market in 2005 for diabetes. Over the next 16 years, iterative improvements led to semaglutide (Wegovy, approved 2021) achieving 15-17% weight loss — transforming obesity from an intractable condition into a treatable one.

Then

GLP-1 drugs became the fastest-growing drug class in history, with semaglutide and tirzepatide generating tens of billions in annual revenue.

Now

The 34-year journey from basic science to blockbuster drug showed that obesity pathways require patient, iterative development. But GLP-1 drugs cause significant lean mass loss and weight regain upon stopping, leaving room for complementary approaches.

Why this matters now

The SLIT3 pathway is at the very beginning of a development arc that took GLP-1 drugs three decades to complete. The realistic timeline to a brown fat drug, if the pathway holds, is measured in years to decades — not months. But the GLP-1 precedent also shows that a fundamentally new mechanism can eventually reshape an entire therapeutic category.

December 1994

Leptin discovery and the obesity drug disappointment (1994)

Jeffrey Friedman at Rockefeller University cloned the ob gene and its protein leptin, revealing for the first time that fat tissue secretes a hormone regulating body weight. The ob/ob mouse, which lacked leptin, was massively obese; injecting leptin caused dramatic weight loss. Amgen licensed the rights for $20 million and rushed to clinical trials.

Then

Leptin administration had minimal effect in most obese humans, who already had high leptin levels and were resistant to it. The drug failed as a general obesity therapy.

Now

Leptin reshaped the entire field's understanding of adipose tissue as an endocrine organ. It eventually found a niche treating rare congenital leptin deficiency. The failure taught researchers that a pathway proven in mice can work entirely differently in obese humans.

Why this matters now

The SLIT3 discovery faces the same translational question: will a mechanism validated in mice and in human tissue samples hold up when tested as a drug in living obese patients? The 1,500-person tissue analysis is a stronger starting point than leptin had, but the history counsels caution about the gap between biological insight and therapeutic impact.

2015-2020

Mirabegron brown fat trials (2015-2020)

Aaron Cypess at the National Institutes of Health tested mirabegron, an already-approved bladder drug that activates beta-3 adrenergic receptors, as a brown fat activator. At four times the approved dose, it lit up brown fat on PET scans and raised resting metabolic rate by about 200 calories per day — the most successful chemical activation of human brown fat to date.

Then

Chronic treatment improved insulin sensitivity, HDL cholesterol, and brown fat metabolic activity. But it produced no significant weight loss and caused cardiovascular side effects at effective doses.

Now

The result proved brown fat can be pharmacologically activated in humans but suggested that simply switching it on isn't enough. The tissue may need structural enhancement — more blood vessels, more nerve connections — to burn calories at a meaningful scale.

Why this matters now

Mirabegron's failure is precisely the problem Shamsi's SLIT3 research addresses. Rather than trying to flip brown fat's activation switch, the new approach builds the vascular and neural infrastructure the tissue needs to function. It's a direct response to the lesson mirabegron taught.