Generation of transgenic mice expressing a FRET biosensor, SMART, that responds to necroptosis

Hypoxia Contributes to the Early-Stage Progression of Necrotizing Sialometaplasia

Necrotizing sialometaplasia (NSM) is a nonneoplastic lesion listed in the World Health Organization Classification of Tumours-Head and Neck Tumours. In early NSM lesion, there is infarction and necrosis of the acinar cells, and squamous metaplasia of the salivary ducts occurs as the lesion matures. Differentiation from squamous cell carcinoma and other malignancies is sometimes required clinically and histopathologically. Local hypoxia caused by trauma and vascular compromise is a proposed etiology of NSM. However, the mechanisms underlying the pathogenesis are unclear. This study focused on the early stages of NSM. Histopathologic observations revealed that the region showing acinar necrosis contained myoepithelial cells with reticular arrangement. Hypoxic in vitro experiments using mouse salivary gland organoids revealed that myoepithelial and basal cells were more tolerant to hypoxia than acinar cells. Moreover, the residual myoepithelial cells in NSM and hypoxia-tolerant cells in organoids expressed transforming growth factor-β3 (TGFB3), which plays a critical role in cell proliferation and squamous metaplasia. Organoid experiments have also replicated the process of squamous metaplasia in NSM during hypoxia and the resolution of hypoxia. Thus, this study demonstrated that hypoxia is a possible etiology of NSM based on the results of histopathologic and in vitro experimental observations.

SDHAF1 confers metabolic resilience to aging hematopoietic stem cells by promoting mitochondrial ATP production

Aging generally predisposes stem cells to functional decline, impairing tissue homeostasis. Here, we report that hematopoietic stem cells (HSCs) acquire metabolic resilience that promotes cell survival. High-resolution real-time ATP analysis with glucose tracing and metabolic flux analysis revealed that old HSCs reprogram their metabolism to activate the pentose phosphate pathway (PPP), becoming more resistant to oxidative stress and less dependent on glycolytic ATP production at steady state. As a result, old HSCs can survive without glycolysis, adapting to the physiological cytokine environment in bone marrow. Mechanistically, old HSCs enhance mitochondrial complex II metabolism during stress to promote ATP production. Furthermore, increased succinate dehydrogenase assembly factor 1 (SDHAF1) in old HSCs, induced by physiological low-concentration thrombopoietin (TPO) exposure, enables rapid mitochondrial ATP production upon metabolic stress, thereby improving survival. This study provides insight into the acquisition of resilience through metabolic reprogramming in old HSCs and its molecular basis to ameliorate age-related hematopoietic abnormalities.

Necroptosis and Its Involvement in Various Diseases

Necroptosis is a regulated form of cell death involved in the development of various pathological conditions. In contrast to apoptosis, plasma membrane rupture (PMR) occurs in cells in the relatively early stage of necroptosis; therefore, necroptosis induces a strong inflammatory response. Stimuli, including tumor necrosis factor (TNF), interferon (IFN)α/β, lipopolysaccharide, polyI:C, and viral infection, induce the formation of necrosomes that lead to membrane rupture and the release of intracellular contents, termed danger-associated molecular patterns (DAMPs). DAMPs are the collective term for molecules that normally reside in the cytoplasm or nucleus in living cells without inducing inflammation but induce strong inflammatory responses when released outside cells. Recent studies have provided a better understanding of the mechanisms underlying PMR and the release of DAMPs. Moreover, necroptosis is involved in various pathological conditions, and mutations in necroptosis-related genes can cause hereditary autoinflammatory syndromes. Thus, manipulating necroptosis signaling pathways may be useful for treating diseases involving necroptosis.