Epigenetic erosion of H4K20me1 induced by inflammation drives aged stem cell ferroptosis

Aging is associated with a decline in stem cell functionality and number across the organism. In this study, we aimed to further unravel Muscle Stem Cells (MuSCs) aging by assessing how systemic factors influence MuSC fate decisions through long-term epigenetic landscape remodelling. As aging is intricately linked to a pro-inflammatory shift, we studied the epigenetic effects of inflammatory signals in MuSCs and measured decreased H4K20me1 levels. This loss disrupts MuSC quiescence, largely through epigenetic silencing of Notch target genes. In the setting of inflammatory signals or aging, the lack of Kmt5a and the subsequent absence of de novoH4K20me1 culminate in cell death by ferroptosis. Aged MuSCs manifest abnormal iron metabolism and reduced Gpx4 levels, resulting in the accumulation of intracellular iron, increased reactive oxygen species, genomic instability, and lipid peroxidation. We showed that ferroptosis is the predominant mode of cell death in aged MuSCs, with remarkably high levels of lipid peroxidation; a phenomenon we also observed in aged hematopoietic stem cells. Implementing preventative strategies to inhibit systemic inflammation prevented aged MuSC ferroptosis, preserving their numbers and regenerative capabilities. This intervention significantly enhanced aged muscle regeneration and strength recovery and extended both lifespan and healthspan in mice. This study delineates a previously underappreciated fate trajectory for stem cell aging, and offers meaningful insights into the treatment of age-related disorders.

Abstract 74: Osteoblasts efferocytosis in bone marrow microenvironment induces osteoblasts’ senescence and apoptosis

Increased cellular apoptosis is commonly seen in myelodysplastic syndrome (MDS), but how clearance of apoptotic cells, especially neutrophils, impacts disease progression is unknown. Moreover, while dysfunction of bone marrow (BM) stromal cell populations has been described in patients with MDS, the mechanisms inducing stromal defects are not well understood. Our laboratory found that BM macrophages are defective in a murine model of MDS (Vav-Nup98 HoxD13, aka NHD13), with decreased efferocytotic rates and increased inflammatory mediators. The increased apoptotic burden and defective macrophages would be expected to recruit non-professional phagocytes (osteoblasts) in the bone and bone marrow. Based on these data, we hypothesize that OBs (osteoblasts) participate in the clearance of apoptotic cells in the bone marrow microenvironment (BMME) to maintain BM homeostasis. However, the increased osteoblastic efferocytosis burden in MDS contributes to OBs’ dysfunction as a mechanism of MDS-dependent BMME disruption that may lead to MDS progression.

We isolated from wild-type (B6) mice bone-associated cells (BAC), which are enriched with OBs. In vitro co-culture with labeled human end-stage neutrophils at 1:1 and 1:10 (OB: PMN) increased OB apoptosis, while senescence was increased only in high-dose PMN co-culture. We found that these changes were cell-autonomous. In vivo injection of neutrophils into WT mice showed around 5-10% efferocytosis rate in OBs. In efferocytotic OBs, apoptosis rates were significantly increased. Together, these data show that OBs participate in efferocytosis and that efferocytosis disrupts OBs, causing apoptosis and senescence.

To mimic the MDS microenvironment, we used a genetic model where one of the Isocitrate dehydrogenase 2 (IDH2) mutations found in MDS (R140Q) is targeted to hematopoietic cells via the Vav promoter (IDH2R140Q mice) as well as NHD13 mice, representing early and late MDS BMME respectively. We observed that 6-to-8 months old NHD13 mice experienced more end-stage neutrophils[CL1] in the BMME (4.6% rate of end-stage neutrophils in WT compared to 9.5% rate in NHD13 mice), where OB apoptosis was also increased in vivo. In IDH2R140Q mice at 3 months of age, we confirmed the presence of mutated IDH2 in bone marrow cells by increased intracellular levels of the oncometabolite 2-hydroxyglutarate. At this early time point, IDH2R140Q mice did not have increased rates of apoptosis in CD45+ cells, and we found no increase in OB apoptosis. Analysis of IDH2R140Q mice at later time points is ongoing.

Our data identify novel mechanisms to explain the relationship between defective myeloid cells and OB apoptosis in MDS that may contribute to the inflammatory MDS microenvironment, impact disease progression, and serve as future therapeutic approaches for MDS patients.

Citation Format: Chunmo Chen, Emily R. Quarato, Yuko Kawano, Noah A. Salama, Hiroki Kawano, Michael W. Becker, Jeevisha Bajaj, Laura Calvi. Osteoblasts efferocytosis in bone marrow microenvironment induces osteoblasts’ senescence and apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 74.

Acute thyrotoxicosis secondary to destructive thyroiditis associated with cardiac catheterization contrast dye

BACKGROUND

Thyrotoxicosis caused by destructive thyroiditis is self-limited and results from the subacute release of preformed thyroid hormone. Common etiologies include painful subacute thyroiditis and silent (painless) subacute thyroiditis (including postpartum thyroiditis, amiodarone-associated destructive thyroiditis, and lithium-associated thyroiditis). Thyrotoxicosis commonly evolves slowly over a matter of weeks.

PATIENT FINDINGS

We report a unique case of severe thyrotoxicosis caused by acute- onset painful destructive thyroiditis in a patient who received large amounts of nonionic contrast dye Hexabrix® for cardiac catheterization. The results of thyroid function and physical examination were normal before the catheterization.

SUMMARY

The acute onset of severe thyroid pain, rapid increase in serum Free Thyroxine Index, and thyroglobulin concentrations with a triiodothyronine to free thyroxine index ratio of < 20 to 1 were compatible with an acute onset destructive thyroiditis, likely related to direct toxicity from the iodinated contrast material.

CONCLUSIONS

In light of the large number of patients who receive these contrast agents during cardiac catheterization, clinicians should be advised of this potentially serious complication, particularly in the setting of unstable cardiac disease.

Disseminated histoplasmosis in a cat in Europe

A cat was presented with a history of vomiting, decreased appetite and weight loss. Abnormal findings were poor body condition, pale mucous membranes, dehydration and a palpable abdominal mass. Abdominal ultrasound showed lymph node enlargement, a mass of uncertain origin, thickening of the muscularis layer of the small bowel, focal thickening of the ileum with loss of layering and free peritoneal fluid. Cytology revealed a piogranulomatous infiltrate and numerous macrophages containing oval or round yeast‐like cells 2 to 5 µm diameter with a central, spherical, lightly basophilic body surrounded by a clear halo, compatible with Histoplasma capsulatum, within the cytoplasm. Post‐mortem examination revealed cavity effusions, granulomatous nodules in lungs, intestine and omentum, thickened intestinal walls and intestinal perforation. Staining with Grocott and immunohistochemistry (IHC) revealed numerous organisms within the granulomatous reaction. H. capsulatum has a worldwide distribution in temperate and subtropical climates. To the author’s knowledge, this is the first report of feline histoplasmosis in Europe.

The interplay of osteogenesis and hematopoiesis: expression of a constitutively active PTH/PTHrP receptor in osteogenic cells perturbs the establishment of hematopoiesis in bone and of skeletal stem cells in the bone marrow

The ontogeny of bone marrow and its stromal compartment, which is generated from skeletal stem/progenitor cells, was investigated in vivo and ex vivo in mice expressing constitutively active parathyroid hormone/parathyroid hormone-related peptide receptor (PTH/PTHrP; caPPR) under the control of the 2.3-kb bone-specific mouse Col1A1 promoter/enhancer. The transgene promoted increased bone formation within prospective marrow space, but delayed the transition from bone to bone marrow during growth, the formation of marrow cavities, and the appearance of stromal cell types such as marrow adipocytes and cells supporting hematopoiesis. This phenotype resolved spontaneously over time, leading to the establishment of marrow containing a greatly reduced number of clonogenic stromal cells. Proliferative osteoprogenitors, but not multipotent skeletal stem cells (mesenchymal stem cells), capable of generating a complete heterotopic bone organ upon in vivo transplantation were assayable in the bone marrow of caPPR mice. Thus, PTH/PTHrP signaling is a major regulator of the ontogeny of the bone marrow and its stromal tissue, and of the skeletal stem cell compartment.

Ultrastructural evidence of the degenerative events occurring during embryogenesis of the filarial nematode Brugia pahangi after tetracycline treatment

Intracellular bacteria belonging to the genus Wolbachia have been described in filarial nematodes and these microorganisms appear to have evolved an obligatory mutualistic association with their filarial hosts. In fact, antibiotic treatment leads to the clearance of bacteria from worms resulting in a block in embryogenesis and, eventually, death of adult filariae. Currently, the antifilarial action of antibiotic treatment is interpreted as a secondary consequence of the bacteriostatic activity against Wolbachia endosymbionts. Here, we demonstrate by transmission electron microscopy the degenerative events occurring during embryogenesis of Brugia pahangi after tetracycline treatment. After 56 days of treatment the cytoplasm of hypodermal cords was totally void of Wolbachia and numerous vacuoles, residual of cytolitic activity, were observed. In the ovary, the morphology of the oocytes was well conserved 33 days after treatment, but the texture of symbiotic bacteria appeared altered. After 56 days of treatment embryogenesis was dramatically affected and the terminal portion of the ovary appeared totally empty. The authors suggest that the symbiotic bacteria play a direct role in worm metabolism and a long-term bacteriostatic effect may block bacterial activity involved in the active control of cytolysis. As a consequence, the bacteriophorous vacuole is transformed into a digestive vacuole and the whole symbiotic population is disrupted.

SOD1 missense mutation in an Italian family with ALS

We have discovered a new Italian pedigree with autosomal-dominant ALS. The pedigree, at present, comprises 75 members distributed in five generations. ALS was diagnosed in eight patients. The mean +/- SD age of onset of the disease was 46.8 +/- 13.5 years, with a range of 29 to 63 years. The mean +/- SD duration of the disease was 11.6 +/- 1.7 months. Molecular genetic studies showed a missense mutation (Gly-->Ser, codon 41) in exon 2 of the Cu/Zn superoxide dismutase gene (SOD1) on chromosome 21 in the available affected member and in 45% of the at-risk subjects of the pedigree. This study confirms the presence of SOD1 point mutations in families with autosomal-dominant ALS and suggests that additional genetic or environmental factors may be involved in the full expression of the disease.

Polyneuropathy secondary to ciguatoxin poisoning

Following ingestion of marine fish in Thailand this patient complained of gastrointestinal and neurological disturbances, marked by severe, mainly motor, demyelinating polyneuropathy, which worsened on her return to Italy a few days later. The clinical pattern, electromyography, cerebrospinal fluid test and sural nerve biopsy by electronmicroscopy permitted the diagnosis of polyneuropathy secondary to ciguatoxin poisoning.