Tirzepatide preserves hematopoietic stem and progenitor cycling while remodeling inflammatory monocytes in obese mice

A recent study explores the effects of Tirzepatide on hematopoietic stem and progenitor cycling in obese mice, while also examining how it alters inflammatory monocytes. Obesity is known to expand myeloid progenitors and increase monocyte production, but the impact of various weight loss methods on hematopoietic stem/progenitor cells (HSPCs), hematopoiesis, and inflammatory cell production remains unclear.

This study compares the hematopoietic compartment in lean, obese, and weight-reduced mice treated with Tirzepatide and those that underwent caloric restriction (CR) to match body weight.

Results showed that caloric restriction led to multilineage cytopenias (reduction in blood lineages), while Tirzepatide maintained blood lineages and specifically reduced classical Ly6Chi CCR2+ monocytes. To understand the mechanisms behind these changes, the researchers performed single-cell mRNA sequencing on bone marrow HSPCs and mature mononuclear blood cells.

They found that caloric restriction suppressed nutrient sensing, proliferation, and oxidative phosphorylation (OXPHOS) gene sets, along with reduced cell cycle activity in HSPCs. In contrast, Tirzepatide-treated HSPCs attenuated these changes. Unlike caloric restriction, Tirzepatide increased suppression of OXPHOS and shifted the maturation spectrum away from classical monocytes when examining cells from HSPCs to mature blood monocytes.

Furthermore, after six weeks of Tirzepatide withdrawal and weight regain, Ly6Chi CCR2+ monocytes returned to levels observed in obese mice. These findings suggest that Tirzepatide uncouples weight loss from the broad hematopoietic suppression seen in caloric restriction by preserving progenitor activity but selectively remodeling inflammatory/classical monocytes.

The study demonstrates that different weight loss modalities have varying impacts on hematopoietic adaptation, providing evidence that classical monocytes may serve as effecter cells through which Tirzepatide may help mitigate obesity-associated inflammation.