Plasma Pyruvate Kinase M2 as a marker of vascular inflammation in giant cell arteritis

Altered Plasma Levels and Tissue Expression of Fibroblast Activation Protein Alpha in Giant Cell Arteritis

OBJECTIVE

Giant cell arteritis (GCA) is characterized by granulomatous inflammation of the medium- and large-sized arteries accompanied by remodeling of the vessel wall. Fibroblast activation protein alpha (FAP) is a serine protease that promotes both inflammation and fibrosis. Here, we investigated the plasma levels and vascular expression of FAP in GCA.

METHODS

Plasma FAP levels were measured with enzyme-linked immunosorbent assay in treatment-naive patients with GCA (n = 60) and polymyalgia rheumatica (PMR) (n = 63) compared with age- and sex-matched healthy controls (HCs) (n = 42) and during follow-up, including treatment-free remission (TFR). Inflamed temporal artery biopsies (TABs) of patients with GCA (n = 9), noninflamed TABs (n = 14), and aorta samples from GCA-related (n = 9) and atherosclerosis-related aneurysm (n = 11) were stained for FAP using immunohistochemistry. Immunofluorescence staining was performed for fibroblasts (CD90), macrophages (CD68/CD206/folate receptor beta), vascular smooth muscle cells (desmin), myofibroblasts (α-smooth muscle actin), interleukin-6 (IL-6), and matrix metalloproteinase-9 (MMP-9).

RESULTS

Baseline plasma FAP levels were significantly lower in patients with GCA compared with patients with PMR and HCs and inversely correlated with systemic markers of inflammation and angiogenesis. FAP levels decreased even further at 3 months on remission in patients with GCA and gradually increased to the level of HCs in TFR. FAP expression was increased in inflamed TABs and aorta of patients with GCA compared with control tissues. FAP was abundantly expressed in fibroblasts and macrophages. Some of the FAP+ fibroblasts expressed IL-6 and MMP-9.

CONCLUSION

FAP expression in GCA is clearly modulated both in plasma and in vessels. FAP may be involved in the inflammatory and remodeling processes in GCA and have utility as a target for imaging and therapeutic intervention.

YKL-40 as a biomarker in various inflammatory diseases: A review

YKL-40 or Chitinase-3-Like Protein 1 (CHI3L1) is a highly conserved glycoprotein that binds heparin and chitin in a non-enzymatic manner. It is a member of the chitinase protein family 18, subfamily A, and unlike true chitinases, YKL-40 is a chitinase-like protein without enzymatic activity for chitin. Although its accurate function is yet unknown, the pattern of its expression in the normal and disease states suggests its possible engagement in apoptosis, inflammation and remodeling or degradation of the extracellular matrix. During an inflammatory response, YKL-40 is involved in a complicated interaction between host and bacteria, both promoting and attenuating immune response and potentially being served as an autoantigen in a vicious circle of autoimmunity. Based on its pathophysiology and mechanism of action, the aim of this review was to summarize research on the growing role of YKL-40 as a persuasive biomarker for inflammatory diseases' early diagnosis, prediction and follow-up (e.g., cardiovascular, gastrointestinal, endocrinological, immunological, musculoskeletal, neurological, respiratory, urinary, infectious) with detailed structural and functional background of YKL-40.

Myelomonocytic cells in giant cell arteritis activate trained immunity programs sustaining inflammation and cytokine production

OBJECTIVE

Trained immunity (TI) is a de facto memory program of innate immune cells, characterized by immunometabolic and epigenetic changes sustaining enhanced production of cytokines. TI evolved as a protective mechanism against infections; however, inappropriate activation can cause detrimental inflammation and might be implicated in the pathogenesis of chronic inflammatory diseases. In this study, we investigated the role of TI in the pathogenesis of giant cell arteritis (GCA), a large-vessel vasculitis characterized by aberrant macrophage activation and excess cytokine production.

METHODS

Monocytes from GCA patients and from age- and sex-matched healthy donors were subjected to polyfunctional studies, including cytokine production assays at baseline and following stimulation, intracellular metabolomics, chromatin immunoprecipitation-qPCR, and combined ATAC/RNA sequencing. Immunometabolic activation (i.e. glycolysis) was assessed in inflamed vessels of GCA patients with FDG-PET and immunohistochemistry (IHC), and the role of this pathway in sustaining cytokine production was confirmed with selective pharmacologic inhibition in GCA monocytes.

RESULTS

GCA monocytes exhibited hallmark molecular features of TI. Specifically, these included enhanced IL-6 production upon stimulation, typical immunometabolic changes (e.g. increased glycolysis and glutaminolysis) and epigenetic changes promoting enhanced transcription of genes governing pro-inflammatory activation. Immunometabolic changes of TI (i.e. glycolysis) were a feature of myelomonocytic cells in GCA lesions and were required for enhanced cytokine production.

CONCLUSIONS

Myelomonocytic cells in GCA activate TI programs sustaining enhanced inflammatory activation with excess cytokine production.

Disease stratification in GCA and PMR: state of the art and future perspectives

Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are closely related conditions characterized by systemic inflammation, a predominant IL-6 signature, an excellent response to glucocorticoids, a tendency to a chronic and relapsing course, and older age of the affected population. This Review highlights the emerging view that these diseases should be approached as linked conditions, unified under the term GCA-PMR spectrum disease (GPSD). In addition, GCA and PMR should be seen as non-monolithic conditions, with different risks of developing acute ischaemic complications and chronic vascular and tissue damage, different responses to available therapies and disparate relapse rates. A comprehensive stratification strategy for GPSD, guided by clinical findings, imaging and laboratory data, facilitates appropriate therapy and cost-effective use of health-economic resources. Patients presenting with predominant cranial symptoms and vascular involvement, who usually have a borderline elevation of inflammatory markers, are at an increased risk of sight loss in early disease but have fewer relapses in the long term, whereas the opposite is observed in patients with predominant large-vessel vasculitis. How the involvement of peripheral joint structures affects disease outcomes remains uncertain and understudied. In the future, all cases of new-onset GPSD should undergo early disease stratification, with their management adapted accordingly.

Metabolic features and glucocorticoid-induced comorbidities in patients with giant cell arteritis and polymyalgia rheumatica in a Dutch and Danish cohort

OBJECTIVES

Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are age-associated inflammatory diseases that frequently overlap. Both diseases require long-term treatment with glucocorticoids (GCs), often associated with comorbidities. Previous population-based cohort studies reported that an unhealthier metabolic profile might prevent the development of GCA. Here, we report metabolic features before start of treatment and during treatment in patients with GCA and PMR.

METHODS

In the Dutch GCA/PMR/SENEX (GPS) cohort, we analysed metabolic features and prevalence of comorbidities (type 2 diabetes, hypercholesterolaemia, hypertension, obesity and cataract) in treatment-naïve patients with GCA (n=50) and PMR (n=42), and compared those with the population-based Lifelines cohort (n=91). To compare our findings in the GPS cohort, we included data from patients with GCA (n=52) and PMR (n=25) from the Aarhus cohort. Laboratory measurements, comorbidities and GC use were recorded for up to 5 years in the GPS cohort.

RESULTS

Glycated haemoglobin levels tended to be higher in treatment-naïve patients with GCA, whereas high-density lipoprotein, low-density lipoprotein and cholesterol levels were lower compared with the Lifelines population. Data from the Aarhus cohort were aligned with the findings obtained in the GPS cohort. Presence of comorbidities at baseline did not predict long-term GC requirement. The incidence of diabetes, obesity and cataract among patients with GCA increased upon initiation of GC treatment.

CONCLUSION

Data from the GCA and PMR cohorts imply a metabolic dysregulation in treatment-naïve patients with GCA, but not in patients with PMR. Treatment with GCs led to the rise of comorbidities and an unhealthier metabolic profile, stressing the need for prednisone-sparing targeted treatment in these vulnerable patients.

Distinct gene signatures of monocytes and B cells in patients with giant cell arteritis: a longitudinal transcriptome analysis

BACKGROUND

Giant cell arteritis (GCA) is a primary large-vessel vasculitis (LVV) of unknown origin. Its management is a challenge due to the late onset of disease symptoms and frequent relapse; therefore, clarifying the pathophysiology of GCA is essential to improving treatment. This study aimed to identify the transition of molecular signatures in immune cells relevant to GCA pathogenesis by analyzing longitudinal transcriptome data in patients.

METHODS

We analyzed the whole blood transcriptome of treatment-naive patients with GCA, patients with Takayasu arteritis (TAK), age-matched, old healthy controls (HCs), and young HCs. Characteristic genes for GCA were identified, and the longitudinal transition of those genes was analyzed using cell-type identification by estimating relative subsets of RNA transcripts (CIBERSORT).

RESULTS

Repeated measures analysis of variance revealed 739 differentially expressed genes among all patients and HCs. Of the 739 genes, 15 were characteristically upregulated and 36 were downregulated in patients with GCA compared to those with TAK and HCs. Pathway enrichment analysis showed that downregulated genes in GCA were associated with B cell activation. CIBERSORT analysis revealed that upregulation of "M0-macrophages" and downregulation of B cells were characteristic of GCA. Upregulation of "M0-macrophages" reflects the activation of monocytes in GCA toward M0-like phenotypes, which persisted under 6 weeks of treatment. Combined treatment with prednisolone and an interleukin-6 receptor antagonist normalized molecular profiles more efficiently than prednisolone monotherapy.

CONCLUSIONS

Gene signatures of monocyte activation and B cell inactivation were characteristic of GCA and associated with treatment response.

Novel PET Imaging of Inflammatory Targets and Cells for the Diagnosis and Monitoring of Giant Cell Arteritis and Polymyalgia Rheumatica

Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are two interrelated inflammatory diseases affecting patients above 50 years of age. Patients with GCA suffer from granulomatous inflammation of medium- to large-sized arteries. This inflammation can lead to severe ischemic complications (e.g., irreversible vision loss and stroke) and aneurysm-related complications (such as aortic dissection). On the other hand, patients suffering from PMR present with proximal stiffness and pain due to inflammation of the shoulder and pelvic girdles. PMR is observed in 40-60% of patients with GCA, while up to 21% of patients suffering from PMR are also affected by GCA. Due to the risk of ischemic complications, GCA has to be promptly treated upon clinical suspicion. The treatment of both GCA and PMR still heavily relies on glucocorticoids (GCs), although novel targeted therapies are emerging. Imaging has a central position in the diagnosis of GCA and PMR. While [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) has proven to be a valuable tool for diagnosis of GCA and PMR, it possesses major drawbacks such as unspecific uptake in cells with high glucose metabolism, high background activity in several non-target organs and a decrease of diagnostic accuracy already after a short course of GC treatment. In recent years, our understanding of the immunopathogenesis of GCA and, to some extent, PMR has advanced. In this review, we summarize the current knowledge on the cellular heterogeneity in the immunopathology of GCA/PMR and discuss how recent advances in specific tissue infiltrating leukocyte and stromal cell profiles may be exploited as a source of novel targets for imaging. Finally, we discuss prospective novel PET radiotracers that may be useful for the diagnosis and treatment monitoring in GCA and PMR.

The Role of PKM2 in Diabetic Microangiopathy

Diabetic microangiopathy is among the most common complications affecting patients with diabetes, and includes both diabetic retinopathy (DR) and diabetic nephropathy (DKD). Diabetic microangiopathy remains a persistent threat to the health and quality of life of affected patients. Mechanistically, the severity of DR and DKD is tied to mitochondrial and glucose metabolism abnormalities, with the activation of the glycolytic enzyme pyruvate kinase M2 (PKM2) contributing to mitochondrial and glomerular dysfunction, abnormal renal hemodynamics, and retinopathy. PKM2 can activate inflammatory bodies in macrophages to promote the release of inflammatory mediators, and serves as a key regulator of inflammatory factors, chemokines and adhesion molecules. As such, there is sufficient evidence that PKM2 can be used as a biomarker for the diagnosis of diabetes and diabetic microangiopathy. Here, we survey the mechanisms whereby PKM2 contributes to diabetes-related microvascular diseases, associated regulatory roles, post-translational modifications, and the potential utility of PKM2 as a therapeutic target. Through this literature review, we have determined that PKM2 offers promise as both a diagnostic marker and therapeutic target with direct relevance to research pertaining to diabetic microangiopathy.