UC Irvine

Importance: Hematopoietic stem cells (HSCs) are foundational to the body's ability to mount an effective immune response, especially when confronted with acute inflammatory stress. Their role in rapidly increasing the number of mature effector leukocytes is essential for effective host defense. In the realm of hematological disorders, Myeloproliferative neoplasm (MPN) presents a significant challenge, primarily due to its effect on HSC function and proliferation.

Objective: Our laboratory previously showed that the antioxidant N-acetylcysteine (N-AC) might have a pivotal role in extending the lifespan of a Jak2V617F knock-in mouse model of MPN. This led to speculations about its protective effects on HSCs, especially against chronic inflammation. This study was consequently formulated with the primary aim to uncover the intricate mechanism by which N-AC shields HSCs from excessive proliferation when faced with inflammation.

Methods: We developed a protocol to examine the cell cycle status of HSCs, particularly after stimulation with lipopolysaccharide (LPS) — a known inflammatory agent. Mice were assigned into two groups randomly: one group received N-AC in their drinking water over a span of ten days, while the control group was given regular water. Mice were injected intra-peritoneally (IP) with lipopolysaccharide (LPS) at 1μg/mouse, and subsequently euthanized 16 hours later. Bone marrow was harvested from the four long bones of the hind limbs. Thereafter, staining procedures were employed to identify HSC-specific surface markers. Advanced techniques, involving the nuclear antigen, Ki67, and the DNA binding dye, DAPI, were used to determine cell cycling.

Results: The inflammation triggered by LPS led to a marked elevation in HSC division, a fact underscored by the surge in the percentage of cells in the G1 phase of the cell cycle. However, a notable observation was that the N-AC administered group exhibited a significant attenuation in this LPS-induced HSC cycling.

Conclusion and Relevance: Our findings illuminate the protective potential of N-AC against inflammation-induced exhaustion in HSCs. With HSCs being fundamental to hematological health, the therapeutic implications of N-AC, particularly for patients grappling with MPN, are profound. This could potentially pave the way for novel therapeutic strategies aimed at preserving the vital functions of HSCs in such patients.