Histiocytic sarcoma in C57BL/6J female mice is associated with liver hematopoiesis: review of 41 cases

Historical Control Data of Spontaneous Pathological Findings in C57BL/6J Mice Used in 18-Month Dietary Carcinogenicity Assays

A retrospective analysis in C57BL6/J mice used in dietary carcinogenicity studies was performed to determine the survival rate, causes of death and incidences of spontaneous non-tumoral and tumoral findings. Data were collected from 1600 mice from control dose groups of sixteen 18-month carcinogenicity assays performed between 2003 and 2021 at the same test facility with similar environmental conditions and experimental procedures. The survival rate was high in both sexes (81%-85%) and the causes of humane euthanasia or death were mainly non-tumoral (chronic ulcerative dermatitis, atrial thrombosis). Benign tumors were more frequent than malignant tumors and females were more affected than males. Pituitary gland adenoma in females, lymphoma, bronchioloalveolar adenoma, and harderian gland adenoma in both sexes were the most common tumors. Systemic amyloidosis, the most frequent non-tumoral lesion, was observed variably across studies without sex predilection. The analysis by cohort (3 time periods of 6 years) showed a tendency toward higher incidences of lymphoma and pituitary gland adenoma and lower incidences of amyloidosis over time. The results presented here provide for the first time a robust set of control historical data in untreated C57BL/6J mice kept for 18 months contributing to build in depth knowledge of this animal model.

The many faces of mouse histiocytic sarcoma in C57BL/6J mice

Histiocytic sarcoma is a tumor of the hematopoietic system considered to be derived from macrophages. Although rare in humans, it occurs frequently in mice. Histiocytic sarcoma can be a difficult tumor to diagnose due to its diverse cellular morphologies, growth patterns, and organ distributions. The varying morphology of histiocytic sarcomas makes it easy to confuse them with other types of neoplasia, including hepatic hemangiosarcoma, uterine schwannoma, leiomyosarcoma, uterine stromal cell tumor, intramedullary osteosarcoma, and myeloid leukemia. As such, immunohistochemistry (IHC) is often needed to differentiate histiocytic sarcomas from other common tumors in mice that they can morphologically mimic. The goal of this article is to present a broader perspective of the diverse cellular morphologies, growth patterns, organ distributions, and IHC labeling of histiocytic sarcomas encountered by the authors. This article describes these features in a set of 62 mouse histiocytic sarcomas, including the IHC characterization of the tumors using a panel of markers for the macrophage antigens F4/80, IBA1, MAC2, CD163, CD68, and lysozyme, and describes differentiating features of histiocytic sarcomas from other morphologically similar tumors. The genetic changes underlying the pathogenesis of histiocytic sarcoma in humans are beginning to be elucidated, but this is difficult due to its rarity. The higher prevalence of this tumor in mice provides opportunities to investigate mechanisms of its development and to test potential treatments.

A Unique Spectrum of Spontaneous Tumors in Dino Knockout Mice Identifies Tissue-Specific Requirements for Tumor Suppression

Here, we report that Dino, a lncRNA required for p53 signaling, suppresses spontaneous tumorigenesis in mice. Dino-/- mice develop significantly more malignant tumors than Dino+/+ littermate controls, consisting predominantly of sarcomas, B cell lymphomas and additional rare tumors. While the prevalence of lymphomas and sarcomas in Dino-/- mice is similar to that of mice with p53 loss, important distinctions emerged. p53-null mice predominantly develop T cell lymphomas; however, no spontaneous T cell lymphoma was observed in Dino-/- mice. Rather than being a phenocopy of the p53-null tumor spectrum, spontaneous tumors in Dino-/- mice resemble the spectrum of human cancers in which DINO is recurrently silenced by methylation in a manner that is mutually exclusive with TP53 alterations, suggesting that similar tissues in human and mouse require DINO for tumor suppression. Consistent with a tissue-specific role for Dino in tumor suppression, loss of Dino had no impact on the development of radiation-induced T cell lymphoma and oncogene-driven medulloblastoma, tumors that are accelerated by the loss of p53. Taken together, these data indicate that Dino serves as a potent tumor suppressor molecule specific to a select subset of tissues in mice and humans.

First reported case of a histiocytic sarcoma in an Armenian hamster (Cricetulus migratorius)

A 14-month-old male Armenian hamster (Cricetulus migratorius) presented with a spontaneous, subcutaneous, firm mass (4.0 × 2.0 × 1.5 cm) on the ventral neck extending towards the cheek pouch causing multifocal small oral ulcerations. This animal was immunized subcutaneously on the dorsal neck for the development of monoclonal antibodies seven months before presentation. The animal was euthanized and necropsy was performed. Histopathology of the mass showed a well demarcated, multilobulated, unencapsulated, highly cellular, neoplastic mass composed of spindle cells arranged in interlacing streams and bundles, with a moderate amount of fibrovascular stroma. The neoplastic cells exhibited indistinct cell borders and a moderate to large amount of eosinophilic, fibrillar cytoplasm, marked anisocytosis and anisokaryosis, binucleated and multinucleated cells, and high mitotic rate. Based on the histomorphologic features of the mass, and the presence of renal tubular hyaline globules and myeloid hyperplasia in the bone marrow, a diagnosis of histiocytic sarcoma was made. The presumptive diagnosis was confirmed by immunohistochemistry, upon which the neoplastic cells showed strong immunoreactivity for the histiocytic cell markers Iba1 and CD11b. Histiocytic sarcomas have been reported in Syrian (Mesocricetus auratus) and Siberian dwarf (Phodopus sungorus) hamsters but, to our knowledge, the current report represents the first case of histiocytic sarcoma described in an Armenian hamster. It is plausible to consider the animal's experimental immunization history and the development of the histiocytic sarcoma to be related. An association between adjuvanted vaccines and soft-tissue sarcomas has been described in cats and referred to as feline injection-site sarcomas.

Disseminated Haemophagocytic Histiocytic Sarcoma in an African Pygmy Hedgehog (Atelerix albiventris)

A 3-year-old intact male African pygmy hedgehog (Atelerix albiventris) was found dead shortly after clinical onset of screaming, aerophagia and lethargy. On gross examination, the spleen was dark red and friable, and the liver was markedly enlarged with a prominent lobular pattern and multiple white nodules. Histopathological examination of liver and spleen revealed dense infiltrates of highly pleomorphic neoplastic, round to polyhedral cells with overt erythrophagocytosis. Similar neoplastic cells were found in the sinuses of the abdominal lymph nodes and in blood vessels in the heart, lung, brain and kidneys. Immunolabelling for CD204 confirmed the histiocytic origin of the neoplastic cells. To our knowledge, this is the first report of a disseminated haemophagocytic histiocytic sarcoma in a hedgehog.

Early-onset aging and mitochondrial defects associated with loss of histone acetyltransferase 1 (Hat1)

Histone acetyltransferase 1 (Hat1) is responsible for the acetylation of newly synthesized histone H4 on lysines 5 and 12 during the process of chromatin assembly. To understand the broader biological role of Hat1, we have generated a conditional mouse knockout model of this enzyme. We previously reported that Hat1 is required for viability and important for mammalian development and genome stability. In this study, we show that haploinsufficiency of Hat1 results in a significant decrease in lifespan. Defects observed in Hat1^+/− mice are consistent with an early‐onset aging phenotype. These include lordokyphosis (hunchback), muscle atrophy, minor growth retardation, reduced subcutaneous fat, cancer, and paralysis. In addition, the expression of Hat1 is linked to the normal aging process as Hat1 mRNA and protein becomes undetectable in many tissues in old mice. At the cellular level, fibroblasts from Hat1 haploinsufficient embryos undergo early senescence and accumulate high levels of p21. Hat1^+/− mouse embryonic fibroblasts (MEFs) display modest increases in endogenous DNA damage but have significantly higher levels of reactive oxygen species (ROS). Consistently, further studies show that Hat1^−/− MEFs exhibit mitochondrial defects suggesting a critical role for Hat1 in mitochondrial function. Taken together, these data show that loss of Hat1 induces multiple hallmarks of early‐onset aging.

Wiskott-Aldrich syndrome gene mutations modulate cancer susceptibility in the p53± murine model

The Wiskott-Aldrich syndrome protein (WASp) is a key regulator of the actin cytoskeleton in hematopoietic cells and mutated in two severe immunodeficiency diseases with high incidence of cancer. Wiskott-Aldrich syndrome (WAS) is caused by loss-of-function mutations in WASp and most frequently associated with lymphoreticular tumors of poor prognosis. X-linked neuropenia (XLN) is caused by gain-of-function mutations in WASp and associated with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). To understand the role of WASp in tumorigenesis, we bred WASp⁺, WASp⁻, and WASp-XLN mice onto tumor susceptible p53^+/- background and sub-lethally irradiated them to enhance tumor development. We followed the cohorts for 24 weeks and tumors were characterized by histology and flow cytometry to define the tumor incidence, onset, and cell origin. We found that p53^+/-WASp⁺ mice developed malignancies, including solid tumors and T cell lymphomas with 71.4% of survival 24 weeks after irradiation. p53^+/-WASp⁻ mice showed lower survival rate and developed various early onset malignancies. Surprisingly, the p53^+/-WASp-XLN mice developed malignancy mostly with late onset, which caused delayed mortality in this colony. This study provides evidence for that loss-of-function and gain-of-function mutations in WASp influence tumor incidence and onset.

Progressive Glomerulonephritis and Histiocytic Sarcoma Associated with Macrophage Functional Defects in CYP1B1-Deficient Mice

The cytochrome P450 CYP1B1 enzyme metabolically activates polycyclic aromatic hydrocarbons and is a major P450 isoenzyme in human monocytes and macrophages. We have shown previously that mice deficient in CYP1B1 were resistant to induced tumors after 7,12-dimethylbenz[a]anthracene exposure. The pathology of aging CYP1B1 null mice on a B6; 129 background was studied in groups of 29 males and 30 females. By 12 months, 50% of the female mice had developed a unusual progressive glomerulonephritis while males had similar renal lesions later in life. This disease followed a sequence of proliferative, membranoproliferative and sclerotic glomerulonephritis. Anti-DNA antibodies were found in the blood of the mice along with immune deposits containing immunoglobulins in subepithelial locations of the glomerular basement membrane. The lesions were unlike those found in aging wild-type B6;129 mice or mice of other strains. We found that macrophages from CYP1B1-null mice were impaired in the phagocytosis of apoptotic, necrotic, and opsonized cells. This suggests a generalized defect in the phagocytic activity of CYP1B1-null mouse macrophages. Male mice also developed a high incidence (62—64%) of histiocytic sarcomas. Our study provides evidence that deficiency of CYP1B1 can play a role in the development of glomerular disease, normal processing of catabolic DNA and tumors of the mononuclear phagocyte system. The function of CYP1B1 in histiocytes and macrophages may involve both self-tolerance and tumor suppression.

Chromosome Condensation 1-Like (Chc1L) Is a Novel Tumor Suppressor Involved in Development of Histiocyte-Rich Neoplasms

Human chromosomal region 13q14 is a deletion hotspot in prostate cancer, multiple myeloma, and chronic lymphocytic leukemia. This region is believed to host multiple tumor suppressors. Chromosome Condensation 1-like (CHC1L) is located at 13q14, and found within the smallest common region of loss of heterozygosity in prostate cancer. Decreased expression of CHC1L is linked to pathogenesis and progression of both prostate cancer and multiple myeloma. However, there is no direct evidence for CHC1L’s putative tumor suppressing role in current literature. Presently, we describe the generation and characterization of Chc1L knockout mice. Chc1L^-/- mice do not develop cancer at a young age, but bone marrow and spleen cells from 8–12 week-old mice display an exaggerated proliferative response. By approximately two years of age, knockout and heterozygote mice have a markedly increased incidence of tumorigenesis compared to wild-type controls, with tumors occurring mainly in the spleen, mesenteric lymph nodes, liver and intestinal tract. Histopathological analysis found that most heterozygote and knockout mice succumb to either Histiocytic Sarcoma or Histiocyte-Associated Lymphoma. Our study suggests that Chc1L is involved in suppression of these two histiocyte-rich neoplasms in mice and supports clinical data suggesting that CHC1L loss of function is an important step in the pathogenesis of cancers containing 13q14 deletion.

Immunohistochemical detection of possible cellular origin of hepatic histiocytic sarcoma in mice

Histiocytic sarcoma (HS) spontaneously arises in the liver in mice ; however, the cellular origins of hepatic HS have not been fully clarified. In this study, we immunohistochemically analyzed 18 cases of hepatic HS from the archives of our previous experiments. In all cases, the tumor cells showed positive reactions for the macrophage-specific markers F4/80 and CD68. The cells were negative for mesenchymal cell and lymphoid cell markers, suggesting that germ cell tumor or lymphoma components do not coexist in the neoplasm. We detected scattered Ly6C(+)F4/80(-) macrophage precursors in the extramedullary hematopoietic foci and liver tissue around the HS lesions. We also showed that certain populations of HS cells express the Ly-6C antigen. These findings suggest that Ly-6C(+) macrophage progenitor cells are a possible cellular origin of murine hepatic HS. Our study identified a novel phenotype of murine HS in two of 18 cases. These cases showed the nodular accumulations of tumor cells with cohesive cytoplasm mimicking the features of epithelioid granuloma. In agreement with the expression of CD204 in epithelioid cells in granulomatous diseases, these HS cells hardly expressed CD204, although the common type HS cells were strongly positive for this antigen. These data suggest that hepatic HS may stem from Ly-6C(+) macrophage precursors. Furthermore, a subset of hepatic HS cases can possibly differentiate into epithelioid cell-like phenotypes.

Extramedullary hematopoiesis: a new look at the underlying stem cell niche, theories of development, and occurrence in animals

Extramedullary hematopoiesis (EMH) is the formation and development of blood cells outside the medullary spaces of the bone marrow. Although widely considered an epiphenomenon, secondary to underlying primary disease and lacking serious clinical or diagnostic implications, the presence of EMH is far from incidental on a molecular basis; rather, it reflects a well-choreographed suite of changes involving stem cells and their microenvironment (the stem cell niche). The goals of this review are to reconsider the molecular basis of EMH based on current knowledge of stem cell niches and to examine its role in the pathophysiologic mechanisms of EMH in animals. The ability of blood cells to home, proliferate, and mature in extramedullary tissues of adult animals reflects embryonic patterns of hematopoiesis and establishment or reactivation of a stem cell niche. This involves pathophysiologic alterations in hematopoietic stem cells, extracellular matrix, stromal cells, and local and systemic chemokines. Four major theories involving changes in stem cells and/or their microenvironment can explain the development of most occurrences of EMH: (1) severe bone marrow failure; (2) myelostimulation; (3) tissue inflammation, injury, and repair; and (4) abnormal chemokine production. EMH has also been reported within many types of neoplasms. Understanding the concepts and factors involved in stem cell niches enhances our understanding of the occurrence of EMH in animals and its relationship to underlying disease. In turn, a better understanding of the prevalence and distribution of EMH in animals and its molecular basis could further inform our understanding of the hematopoietic stem cell niche.

The histopathologic and molecular basis for the diagnosis of histiocytic sarcoma and histiocyte-associated lymphoma of mice

Histiocytic sarcoma (HS) and histiocyte-associated lymphoma (HAL) of mice are difficult to distinguish histologically. Studies of multiple cases initially diagnosed as HS or HAL allowed us to define HS as round, fusiform, or mixed cell types that were F4/80+, Mac-2+, and PAX5-; that lacked markers for other sarcomas; and that had immune receptor genes in germline configuration. Two other subsets had clonal populations of lymphocytes. The first, HAL, featured malignant lymphocytes admixed with large populations of normal-appearing histiocytes. The second appeared to be composites of lymphoma and HS. Several cases suggestive of B myeloid-lineage plasticity were also observed.

Genetic susceptibility to chronic hepatitis is inherited codominantly in Helicobacter hepaticus-infected AB6F1 and B6AF1 hybrid male mice, and progression to hepatocellular carcinoma is linked to hepatic expression of lipogenic genes and immune function-associated networks

Helicobacter hepaticus causes hepatitis in susceptible strains of mice. Previous studies indicated that A/JCr mice are susceptible and C57BL/6NCr mice are resistant to H. hepaticus-induced hepatitis. We used F1 hybrid mice derived from A/J and C57BL/6 matings to investigate their phenotype and determine their hepatic gene expression profile in response to H. hepaticus infection. F1 hybrid mice, as well as parental A/J and C57BL/6 mice, were divided equally into control and H. hepaticus-infected groups and euthanized at 18 months postinoculation. Hepatic lesions were evaluated histologically and the differential hepatic gene expression in F1 mice was determined by microarray-based global gene expression profiling analysis. H. hepaticus-infected parental strains including A/J and C57BL/6 mice, as well as F1 mice, developed significant hepatitis. Overall, hepatocellular carcinomas or dysplastic liver lesions were observed in 69% of H. hepaticus-infected F1 male mice and H. hepaticus was isolated from hepatic tissues of all F1 mice with liver tumors. Liver tumors, characterized by hepatic steatosis, developed in livers with high hepatitis scores. To identify gene expression specific to H. hepaticus-induced hepatitis and progression to hepatocellular carcinoma in F1 mice, a method using comparative group transcriptome analysis was utilized. The canonical pathway most significantly enriched was immunological disease. Fatty acid synthase and steaoryl-coenzyme A desaturase, the two rate-limiting enzymes in lipogenesis, were upregulated in neoplastic relative to dysplastic livers. This study suggests a synergistic interaction between hepatic steatosis and infectious hepatitis leading to hepatocellular carcinoma. The use of AB6F1 and B6AF1 mice, as well as genetically engineered mice, on a C57BL/6 background will allow studies investigating the role of chronic microbial hepatitis and steatohepatitis in the pathogenesis of liver cancer.

High incidence, early onset of histiocytic sarcomas in mice with Hertwig's anemia

OBJECTIVE

Histiocytic sarcoma (HS) is a rare, rapidly disseminated, usually lethal tumor in humans. Treatment specific for HS has not been developed primarily due to deficiencies of appropriate animal models with high incidence/early onset. Mice with Hertwig's anemia (an/an) provide a potential model.

METHODS

Here, we compare HS susceptibility in an/an and unaffected control mice maintained on three genetic backgrounds. As a potential therapeutic measure, genetically marked bone marrow is transplanted between high and low susceptibility animals.

RESULTS

HS is detected earlier and the overall incidence is 15-fold higher in WBB6F1(F1)-an/an than in F1-+/?, B6-an/an and -+/? mice. Neither WB-an/an nor their normal WB-+/? littermates present with HS. Liver myelopoiesis and aneuploidy coexist with HS but the former is also rampant (33.7% incidence) in HS-free +/? and an/an mice. Marrow transplantation experiments provide evidence that (1) myelopoiesis is associated with HS and (2) early-onset/high-incidence HS is blocked by using late-onset F1-+/+ mice, as either donor or recipient.

CONCLUSIONS

Homozygosity for an on an F1 genetic background is essential for high-incidence/early-onset HS; myelopoiesis and HS coexist; and therapeutic transplantation may be feasible.