Characterization and modulation of the pro-inflammatory effects of immune cells in the canine intervertebral disk

Background

Intervertebral disk (IVD) degeneration affects both humans and canines and is a major cause of low back pain (LBP). Mast cell (MC) and macrophage (MØ) infiltration has been identified in the pathogenesis of IVD degeneration (IVDD) in the human and rodent model but remains understudied in the canine. MC degranulation in the IVD leads to a pro-inflammatory cascade and activates protease activated receptor 2 (PAR2) on IVD cells. The objectives of the present study are to: (1) highlight the pathophysiological changes observed in the degenerate canine IVD, (2) further characterize the inflammatory effect of MCs co-cultured with canine nucleus pulposus (NP) cells, (3) evaluate the effect of construct stiffness on NP and MCs, and (4) identify potential therapeutics to mitigate pathologic changes in the IVD microenvironment.

Methods

Canine IVD tissue was isolated from healthy autopsy research dogs (beagle) and pet dogs undergoing laminectomy for IVD herniation. Morphology, protein content, and inflammatory markers were assessed. NP cells isolated from healthy autopsy (Mongrel hounds) tissue were co-cultured with canine MCs within agarose constructs and treated with cromolyn sodium (CS) and PAR2 antagonist (PAR2A). Gene expression, sulfated glycosaminoglycan content, and stiffness of constructs were assessed.

Results

CD 31+ blood vessels, mast cell tryptase, and macrophage CD 163+ were increased in the degenerate surgical canine tissue compared to healthy autopsy. Pro-inflammatory genes were upregulated when canine NP cells were co-cultured with MCs and the stiffer microenvironment enhanced these effects. Treatment with CS and PAR2 inhibitors mediated key pro-inflammatory markers in canine NP cells.

Conclusion

There is increased MC, MØs, and vascular ingrowth in the degenerate canine IVD tissue, similar to observations in the clinical population with IVDD and LBP. MCs co-cultured with canine NP cells drive inflammation, and CS and PAR2A are potential therapeutics that may mitigate the pathophysiology of IVDD in vitro.

Resistance to PRMT5-targeted therapy in mantle cell lymphoma

ABSTRACT

Mantle cell lymphoma (MCL) is an incurable B-cell non-Hodgkin lymphoma, and patients who relapse on targeted therapies have poor prognosis. Protein arginine methyltransferase 5 (PRMT5), an enzyme essential for B-cell transformation, drives multiple oncogenic pathways and is overexpressed in MCL. Despite the antitumor activity of PRMT5 inhibition (PRT-382/PRT-808), drug resistance was observed in a patient-derived xenograft (PDX) MCL model. Decreased survival of mice engrafted with these PRMT5 inhibitor-resistant cells vs treatment-naive cells was observed (P = .005). MCL cell lines showed variable sensitivity to PRMT5 inhibition. Using PRT-382, cell lines were classified as sensitive (n = 4; 50% inhibitory concentration [IC50], 20-140 nM) or primary resistant (n = 4; 340-1650 nM). Prolonged culture of sensitive MCL lines with drug escalation produced PRMT5 inhibitor-resistant cell lines (n = 4; 200-500 nM). This resistant phenotype persisted after prolonged culture in the absence of drug and was observed with PRT-808. In the resistant PDX and cell line models, symmetric dimethylarginine reduction was achieved at the original PRMT5 inhibitor IC50, suggesting activation of alternative resistance pathways. Bulk RNA sequencing of resistant cell lines and PDX relative to sensitive or short-term-treated cells, respectively, highlighted shared upregulation of multiple pathways including mechanistic target of rapamycin kinase [mTOR] signaling (P < 10-5 and z score > 0.3 or < 0.3). Single-cell RNA sequencing analysis demonstrated a strong shift in global gene expression, with upregulation of mTOR signaling in resistant PDX MCL samples. Targeted blockade of mTORC1 with temsirolimus overcame the PRMT5 inhibitor-resistant phenotype, displayed therapeutic synergy in resistant MCL cell lines, and improved survival of a resistant PDX.

Mouse Model of Spinal Cord Hypoperfusion with Immediate Paralysis Caused by Endovascular Repair of Thoracic Aortic Aneurysm

BACKGROUND

A clinically relevant mouse model of thoracic endovascular aortic repair-induced ischemic spinal cord injury has been lacking since the procedure was first employed in 1991. The hypothesis was that ligation of mouse intercostal arteries would simulate thoracic endovascular aortic repair-induced ischemic spinal cord injury and behavioral deficit. The aim was to create a mouse model of thoracic endovascular aortic repair-induced spinal cord hypoperfusion by ligating five pairs of mouse intercostal vessels.

METHODS

Mice were divided into sham (n = 53) and ligation (n = 60) groups. The procedures called for double ligation of three pairs and single ligation of two pairs of thoracic intercostal arteries in adult C57BL/6 mice. A laser Doppler probe was used in vivo on the spinal cords and intercostal arteries to document the extent of arterial ligation and spinal cord hypoperfusion. The Basso Mouse Scale for Locomotion, histological studies, and electron microscopy demonstrated postligation locomotive and histopathological changes.

RESULTS

Ligation induced a significant and instantaneous drop in blood flow in the intercostal arteries (% change; mean = -63.81; 95% CI, -72.28 to -55.34) and the thoracic spinal cord (% change; mean = -68.55; 95% CI, -80.23 to -56.87). Paralysis onset was immediate and of varying degree, with behavioral deficit stratified into three groups: 9.4% exhibited severe paralysis, 37.5% moderate paralysis, and 53.1% mild paralysis at day 1 (n = 32; P < 0.001). Mild and moderate paralysis was transient, gradually improving over time. Severe paralysis showed no improvement and exhibited a higher mortality rate (83%; n = 15 of 18) compared to moderately (33%; n = 6 of 18) and mildly (24%; n = 6 of 25) paralyzed mice (P < 0.001). The overall ligation group survival rate (84%; n = 46 of 55) was significantly lower than the sham group (100%; n = 48 of 48) with P = 0.003.

CONCLUSIONS

The mouse model generates reproducible spinal cord hypoperfusion and accompanying histopathological ischemic spinal cord damage. The resulting anatomical changes and variable behavioral deficits mimic the variability in radiological and clinical findings in human patients.

EDITOR’S PERSPECTIVE

METTL3 Regulates Liver Homeostasis, Hepatocyte Ploidy, and Circadian Rhythm-Controlled Gene Expression in Mice

N6-methyladenosine (m6A), the most abundant internal modifier of mRNAs installed by the methyltransferase 13 (METTL3) at the (G/A)(m6A)C motif, plays a critical role in the regulation of gene expression. METTL3 is essential for embryonic development, and its dysregulation is linked to various diseases. However, the role of METTL3 in liver biology is largely unknown. In this study, METTL3 function was unraveled in mice depleted of Mettl3 in neonatal livers (Mettl3fl/fl; Alb-Cre). Liver-specific Mettl3 knockout (M3LKO) mice exhibited global decrease in m6A on polyadenylated RNAs and pathologic features associated with nonalcoholic fatty liver disease (eg, hepatocyte ballooning, ductular reaction, microsteatosis, pleomorphic nuclei, DNA damage, foci of altered hepatocytes, focal lobular and portal inflammation, and elevated serum alanine transaminase/alkaline phosphatase levels). Mettl3-depleted hepatocytes were highly proliferative, with decreased numbers of binucleate hepatocytes and increased nuclear polyploidy. M3LKO livers were characterized by reduced m6A and expression of several key metabolic transcripts regulated by circadian rhythm and decreased nuclear protein levels of the core clock transcription factors BMAL1 and CLOCK. A significant decrease in total Bmal1 and Clock mRNAs but an increase in their nuclear levels were observed in M3LKO livers, suggesting impaired nuclear export. Consistent with the phenotype, methylated (m6A) RNA immunoprecipitation coupled with sequencing and RNA sequencing revealed transcriptome-wide loss of m6A markers and alterations in abundance of mRNAs involved in metabolism in M3LKO. Collectively, METTL3 and m6A modifications are critical regulators of liver homeostasis and function.

A Revised Diagnostic Classification of Canine Glioma: Towards Validation of the Canine Glioma Patient as a Naturally Occurring Preclinical Model for Human Glioma

The National Cancer Institute-led multidisciplinary Comparative Brain Tumor Consortium (CBTC) convened a glioma pathology board, comprising both veterinarian and physician neuropathologists, and conducted a comprehensive review of 193 cases of canine glioma. The immediate goal was to improve existing glioma classification methods through creation of a histologic atlas of features, thus yielding greater harmonization of phenotypic characterization. The long-term goal was to support future incorporation of clinical outcomes and genomic data into proposed simplified diagnostic schema, so as to further bridge the worlds of veterinary and physician neuropathology and strengthen validity of the dog as a naturally occurring, translationally relevant animal model of human glioma. All cases were morphologically reclassified according to a new schema devised by the entire board, yielding a majority opinion diagnosis of astrocytoma (43, 22.3%), 19 of which were low-grade and 24 high-grade, and oligodendroglioma (134, 69.4%), 35 of which were low-grade and 99 were high-grade. Sixteen cases (8.3%) could not be classified as oligodendroglioma or astrocytoma based on morphology alone and were designated as undefined gliomas. The simplified classification scheme proposed herein provides a tractable means for future addition of molecular data, and also serves to highlight histologic similarities and differences between human and canine glioma.

Creation of an NCI comparative brain tumor consortium: informing the translation of new knowledge from canine to human brain tumor patients

On September 14-15, 2015, a meeting of clinicians and investigators in the fields of veterinary and human neuro-oncology, clinical trials, neuropathology, and drug development was convened at the National Institutes of Health campus in Bethesda, Maryland. This meeting served as the inaugural event launching a new consortium focused on improving the knowledge, development of, and access to naturally occurring canine brain cancer, specifically glioma, as a model for human disease. Within the meeting, a SWOT (strengths, weaknesses, opportunities, and threats) assessment was undertaken to critically evaluate the role that naturally occurring canine brain tumors could have in advancing this aspect of comparative oncology aimed at improving outcomes for dogs and human beings. A summary of this meeting and subsequent discussion are provided to inform the scientific and clinical community of the potential for this initiative. Canine and human comparisons represent an unprecedented opportunity to complement conventional brain tumor research paradigms, addressing a devastating disease for which innovative diagnostic and treatment strategies are clearly needed.