Inhibition of furin results in increased growth, invasiveness and cytokine production of synoviocytes from patients with rheumatoid arthritis

Precision nutrition to reset virus-induced human metabolic reprogramming and dysregulation (HMRD) in long-COVID

SARS-CoV-2, the etiological agent of COVID-19, is devoid of any metabolic capacity; therefore, it is critical for the viral pathogen to hijack host cellular metabolic machinery for its replication and propagation. This single-stranded RNA virus with a 29.9 kb genome encodes 14 open reading frames (ORFs) and initiates a plethora of virus-host protein-protein interactions in the human body. These extensive viral protein interactions with host-specific cellular targets could trigger severe human metabolic reprogramming/dysregulation (HMRD), a rewiring of sugar-, amino acid-, lipid-, and nucleotide-metabolism(s), as well as altered or impaired bioenergetics, immune dysfunction, and redox imbalance in the body. In the infectious process, the viral pathogen hijacks two major human receptors, angiotensin-converting enzyme (ACE)-2 and/or neuropilin (NRP)-1, for initial adhesion to cell surface; then utilizes two major host proteases, TMPRSS2 and/or furin, to gain cellular entry; and finally employs an endosomal enzyme, cathepsin L (CTSL) for fusogenic release of its viral genome. The virus-induced HMRD results in 5 possible infectious outcomes: asymptomatic, mild, moderate, severe to fatal episodes; while the symptomatic acute COVID-19 condition could manifest into 3 clinical phases: (i) hypoxia and hypoxemia (Warburg effect), (ii) hyperferritinemia ('cytokine storm'), and (iii) thrombocytosis (coagulopathy). The mean incubation period for COVID-19 onset was estimated to be 5.1 days, and most cases develop symptoms after 14 days. The mean viral clearance times were 24, 30, and 39 days for acute, severe, and ICU-admitted COVID-19 patients, respectively. However, about 25-70% of virus-free COVID-19 survivors continue to sustain virus-induced HMRD and exhibit a wide range of symptoms that are persistent, exacerbated, or new 'onset' clinical incidents, collectively termed as post-acute sequelae of COVID-19 (PASC) or long COVID. PASC patients experience several debilitating clinical condition(s) with >200 different and overlapping symptoms that may last for weeks to months. Chronic PASC is a cumulative outcome of at least 10 different HMRD-related pathophysiological mechanisms involving both virus-derived virulence factors and a multitude of innate host responses. Based on HMRD and virus-free clinical impairments of different human organs/systems, PASC patients can be categorized into 4 different clusters or sub-phenotypes: sub-phenotype-1 (33.8%) with cardiac and renal manifestations; sub-phenotype-2 (32.8%) with respiratory, sleep and anxiety disorders; sub-phenotype-3 (23.4%) with skeleto-muscular and nervous disorders; and sub-phenotype-4 (10.1%) with digestive and pulmonary dysfunctions. This narrative review elucidates the effects of viral hijack on host cellular machinery during SARS-CoV-2 infection, ensuing detrimental effect(s) of virus-induced HMRD on human metabolism, consequential symptomatic clinical implications, and damage to multiple organ systems; as well as chronic pathophysiological sequelae in virus-free PASC patients. We have also provided a few evidence-based, human randomized controlled trial (RCT)-tested, precision nutrients to reset HMRD for health recovery of PASC patients.

Identification of potential biomarkers for SLE through mRNA expression profiling

BACKGROUND

Systemic lupus erythematosus (SLE) is an autoimmune disease that influences numerous body systems. Furin, tristetraprolin (TTP), and NOD, LRR, and pyrin domain-containing protein 3 (NLRP3) contribute in developing autoimmune illnesses.

AIM

Understandthe role of furin, TTP, and NLRP3 mRNA gene expression in SLE pathogenesis and prognosis. Methods: Total 210 individuals were enrolled, divided in two group: cases and control; 105 participants in each group.  Real-time quantitative PCR for furin, TTP,and NLRP3 mRNA gene expression were determined for each subject.

RESULTS

SLE patients showed significantly higher serum furin [median 20.10 (0.0-162.88) in comparison with control group [median 1.10 (0.33-8.64)] with significant pvalue (p < 0.001), for NLRP3 expression [median 7.03 (0.0-282.97) compared to control group [median 1.0 (0.44-9.48)] with significant p value (p = 0.006)but lower TTP [median 2.37 (0.0-30.13)] in comparison with control group [median 7.90 (1.0-29.29)] with significant p value (p < 0.001) . Elevated levels of Furin and NLRP3 and low levels of TTP were linked to increased illness activity.

CONCLUSION

Furin and NLRP increase in SLE and higher with illness activity. TTP is lowerin SLE and negatively correlates with disease activity.

Furin inhibits epithelial cell injury and alleviates experimental colitis by activating the Nrf2-Gpx4 signaling pathway

BACKGROUND AND AIM

Furin is a proprotein convertase reported to have protective effects in several autoimmune diseases. However, the role of furin in ulcerative colitis (UC) remains unclear. We aimed to clarify this role.

METHODS

Furin expression was measured in UC and dextran sulfate sodium (DSS)-induced colitis. Gain- and loss-of-function experiments were conducted to evaluate the effect of furin in UC using DSS-treated NCM460 cells. Several ferroptotic parameters, including cell viability, cell death rate, lipid reactive oxygen species level, mitochondrial membrane damage and glutathione peroxidase 4 (Gpx4) expression, were measured. Exogenous furin was used to treat the DSS-induced colitis in mice to confirm the results in vivo. Finally, the activation of nuclear factor erythroid 2-like 2 (Nrf2) was detected to explore the mechanism.

RESULTS

Furin expression was aberrant in UC. Furin overexpression attenuated DSS-induced ferroptosis-like injury and upregulated Gpx4 in NCM460 cells, whereas silencing furin had the opposite effects. Exogenous furin treatment alleviated DSS-induced colitis in mice by upregulating Gpx4. Mechanistic experiments revealed that furin activated Nrf2 both in vitro and in vivo.

CONCLUSIONS

Furin protects epithelial cells from DSS-induced ferroptosis-like cell injury and alleviates experimental colitis by activating the Nrf2-Gpx4 signaling pathway.

Mouse Models of Human Proprotein Convertase Insufficiency

The kexin-like proprotein convertases perform the initial proteolytic cleavages that ultimately generate a variety of different mature peptide and proteins, ranging from brain neuropeptides to endocrine peptide hormones, to structural proteins, among others. In this review, we present a general introduction to proprotein convertase structure and biochemistry, followed by a comprehensive discussion of each member of the kexin-like subfamily of proprotein convertases. We summarize current knowledge of human proprotein convertase insufficiency syndromes, including genome-wide analyses of convertase polymorphisms, and compare these to convertase null and mutant mouse models. These mouse models have illuminated our understanding of the roles specific convertases play in human disease and have led to the identification of convertase-specific substrates; for example, the identification of procorin as a specific PACE4 substrate in the heart. We also discuss the limitations of mouse null models in interpreting human disease, such as differential precursor cleavage due to species-specific sequence differences, and the challenges presented by functional redundancy among convertases in attempting to assign specific cleavages and/or physiological roles. However, in most cases, knockout mouse models have added substantively both to our knowledge of diseases caused by human proprotein convertase insufficiency and to our appreciation of their normal physiological roles, as clearly seen in the case of the furin, proprotein convertase 1/3, and proprotein convertase 5/6 mouse models. The creation of more sophisticated mouse models with tissue- or temporally-restricted expression of specific convertases will improve our understanding of human proprotein convertase insufficiency and potentially provide support for the emerging concept of therapeutic inhibition of convertases.

Increased FURIN expression in rheumatoid arthritis patients and its anti-inflammatory effect

Background

FURIN belongs to the proprotein convertase family that processes proproteins and is involved in many diseases. However, the role of FURIN in rheumatoid arthritis (RA) remains unknown. In this study, we investigated the association between circulating FURIN and disease activity in patients with RA and the effect of FURIN in THP‐1‐derived macrophages.

Methods

A total of 108 RA patients and 39 healthy controls participants were included in this study. RA patients were divided into four disease activity groups determined by the Disease Activity Score of 28 joints (DAS28). FURIN expression in peripheral blood mononuclear cells (PBMCs) and serum was detected by using quantitative real‐time polymerase chain reaction (qRT‐PCR) and enzyme‐linked immunosorbent assay (ELISA), respectively. Western blotting and qRT‐PCR were used to detect cytokines level after interfering FURIN expressed in THP‐1‐derived macrophages.

Results

Both FURIN mRNA and protein levels were significantly higher in RA patients than in healthy controls participants (P < .001). No significant difference in FURIN expression was observed among the four RA groups (P > .05). Spearman correlation revealed that FURIN positively correlated with transforming growth factor‐β1(TGF‐β1), rheumatoid factor (RF), and anti‐cyclic citrullinated peptide (anti‐CCP). Moreover, the inhibition of FURIN in THP‐1‐derived macrophages promoted the caspase‐1 and IL‐1β expression (P < .05).

Conclusion

FURIN levels were significantly increased in the peripheral blood of RA patients and were not associated with disease activity. The inhibition of FURIN in THP‐1‐derived macrophages with elevated IL‐1β levels shows that FURIN may have an anti‐inflammatory effect.

A novel cell-based sensor detecting the activity of individual basic proprotein convertases

The basic proprotein convertases (PCs) furin, PC1/3, PC2, PC5/6, PACE4, PC4, and PC7 are promising drug targets for human diseases. However, developing selective inhibitors remains challenging due to overlapping substrate recognition motifs and limited structural information. Classical drug screening approaches for basic PC inhibitors involve homogeneous biochemical assays using soluble recombinant enzymes combined with fluorogenic substrate peptides that may not accurately recapitulate the complex cellular context of the basic PC-substrate interaction. Herein we report basic PC sensor (BPCS), a novel cell-based molecular sensor that allows rapid screening of candidate inhibitors and their selectivity toward individual basic PCs within mammalian cells. BPCS consists of Gaussia luciferase linked to a sortilin-1 membrane anchor via a cleavage motif that allows efficient release of luciferase specifically if individual basic PCs are provided in the same membrane. Screening of selected candidate peptidomimetic inhibitors revealed that BPCS can readily distinguish between general and selective PC inhibitors in a high-throughput screening format. The robust and cost-effective assay format of BPCS makes it suitable to identify novel specific small-molecule inhibitors against basic PCs for therapeutic application. Its cell-based nature will allow screening for drug targets in addition to the catalytically active mature enzyme, including maturation, transport, and cellular factors that modulate the enzyme's activity. This broadened 'target range' will enhance the likelihood to identify novel small-molecule compounds that inhibit basic PCs in a direct or indirect manner and represents a conceptual advantage.

Increased expression of the proprotein convertase enzyme FURIN in rheumatoid arthritis

OBJECTIVE

FURIN is a proprotein convertase enzyme that inhibits the proinflammatory function of T cells and myeloid cells. Elevated FURIN expression levels have been reported in immune-mediated diseases, such as primary Sjögren's syndrome. Here, we investigated the levels of FURIN in peripheral blood (PB) and synovial fluid (SF) leucocytes from patients with rheumatoid arthritis (RA).

METHOD

FURIN mRNA expression in PB and SF cells was determined by quantitative reverse transcription-polymerase chain reaction and FURIN plasma levels were measured using enzyme-linked immunosorbent assay. Associations between FURIN levels and demographic and clinical characteristics of the patients were determined.

RESULTS

FURIN levels were significantly elevated in PB and SF mononuclear cells, T cells, and monocytes from RA patients compared to healthy controls. High FURIN levels were significantly associated with the prevailing prednisolone treatment, higher prednisolone doses, and increased C-reactive protein levels and Health Assessment Questionnaire values.

CONCLUSION

FURIN is significantly upregulated in RA PB and SF leucocytes, suggesting that it may have a role in the pathogenesis of RA. In addition, our results suggest that elevated FURIN expression is associated with the indicators of more severe RA.

Serine proteinases in the turnover of the cartilage extracellular matrix in the joint: implications for therapeutics

Cartilage destruction is a key characteristic of arthritic disease, a process now widely established to be mediated by metzincins such as MMPs. Despite showing promise in preclinical trials during the 1990s, MMP inhibitors for the blockade of extracellular matrix turnover in the treatment of cancer and arthritis failed clinically, primarily due to poor selectivity for target MMPs. In recent years, roles for serine proteinases in the proteolytic cascades leading to cartilage destruction have become increasingly apparent, renewing interest in the potential for new therapeutic strategies that utilize pharmacological inhibitors against this class of proteinases. Herein, we describe key serine proteinases with likely importance in arthritic disease and highlight recent advances in this field. LINKED ARTICLES: This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.