Circadian Disruption Primes Myofibroblasts for Accelerated Activation as a Mechanism Underpinning Fibrotic Progression in Non-Alcoholic Fatty Liver Disease

Circadian rhythm governs many aspects of liver physiology and its disruption exacerbates chronic disease. CLOCKΔ19 mice disrupted circadian rhythm and spontaneously developed obesity and metabolic syndrome, a phenotype that parallels the progression of non-alcoholic fatty liver disease (NAFLD). NAFLD represents an increasing health burden with an estimated incidence of around 25% and is associated with an increased risk of progression towards inflammation, fibrosis and carcinomas. Excessive extracellular matrix deposition (fibrosis) is the key driver of chronic disease progression. However, little attention was paid to the impact of disrupted circadian rhythm in hepatic stellate cells (HSCs) which are the primary mediator of fibrotic ECM deposition. Here, we showed in vitro and in vivo that liver fibrosis is significantly increased when circadian rhythm is disrupted by CLOCK mutation. Quiescent HSCs from CLOCKΔ19 mice showed higher expression of RhoGDI pathway components and accelerated activation. Genes altered in this primed CLOCKΔ19 qHSC state may provide biomarkers for early liver disease detection, and include AOC3, which correlated with disease severity in patient serum samples. Integration of CLOCKΔ19 microarray data with ATAC-seq data from WT qHSCs suggested a potential CLOCK regulome promoting a quiescent state and downregulating genes involved in cell projection assembly. CLOCKΔ19 mice showed higher baseline COL1 deposition and significantly worse fibrotic injury after CCl4 treatment. Our data demonstrate that disruption to circadian rhythm primes HSCs towards an accelerated fibrotic response which worsens liver disease

PAK1-dependent mechanotransduction enables myofibroblast nuclear adaptation and chromatin organization during fibrosis.

Myofibroblasts are responsible for scarring during fibrosis. The scar propagates mechanical signals inducing a radical transformation in myofibroblast cell state and increasing profibrotic phenotype. Here, we show mechanical stress from progressive scarring induces nuclear softening and de-repression of heterochromatin. The parallel loss of H3K9Me3 enables a permissive state for distinct chromatin accessibility and profibrotic gene regulation. Integrating chromatin accessibility profiles with RNA expression provides insight into the transcription network underlying the switch in profibrotic myofibroblast states, emphasizing mechanoadaptive regulation of PAK1 as key drivers. Through genetic manipulation in liver and lung fibrosis, loss of PAK1-dependent signaling impairs the mechanoadaptive response in vitro and dramatically improves fibrosis in vivo. Moreover, we provide human validation for mechanisms underpinning PAK1-mediated mechanotransduction in liver and lung fibrosis. Collectively, these observations provide insight into the nuclear mechanics driving the profibrotic chromatin landscape in fibrosis, highlighting actomyosin-dependent mechanisms as potential therapeutic targets in fibrosis

Disrupted autophagy undermines skeletal muscle adaptation and integrity

This review assesses the importance of proteostasis in skeletal muscle maintenance with a specific emphasis on autophagy. Skeletal muscle appears to be particularly vulnerable to genetic defects in basal and induced autophagy, indicating that autophagy is co-substantial to skeletal muscle maintenance and adaptation. We discuss emerging evidence that tension-induced protein unfolding may act as a direct link between mechanical stress and autophagic pathways. Mechanistic links between protein damage, autophagy and muscle hypertrophy, which is also induced by mechanical stress, are still poorly understood. However, some mouse models of muscle disease show ameliorated symptoms upon effective targeting of basal autophagy. These findings highlight the importance of autophagy as therapeutic target and suggest that elucidating connections between protein unfolding and mTOR-dependent or mTOR-independent hypertrophic responses is likely to reveal specific therapeutic windows for the treatment of muscle wasting disorders

Mechanotransduction at the z-disc of skeletal muscle

The importance of the transglutaminase-like protein kyphoscoliosis peptidase (KY) in skeletal muscle was discovered in a KY-deficient mouse model of hereditary kyphoscoliosis (ky/ky). The ky/ky pathology primarily affects muscles experiencing high tension, e.g., the soleus, which undergoes regeneration and shows persistent hallmarks of structural damage, including the aberrant localisation of the z-disc crosslinker Filamin C (FLNC) – a known KY interaction partner. However, muscles are globally smaller in size, and fast-twitch muscles (e.g., the extensor digitorum longus or EDL) show an inability to undergo hypertrophy in response to elevated tension. A robust function for KY has not been identified. Recently reported human cases of KY-deficient myopathy share hallmarks with the mouse pathology and underscore the value of increasing our understanding of KY and its function. Chaperone Assisted Selective Autophagy (CASA) is a tension-induced mechanism for FLNC turnover understood to be critical for muscle maintenance. This thesis hypothesises that the absence of KY disrupts CASA, thereby indicating that KY might have a role in CASA. This thesis examines CASA in the ky/ky mouse model and describes the generation and analysis of novel cellular (C2C12) and zebrafish models of KY-deficiency. These indicate that constitutive upregulation of CASA markers may be a primary hallmark of KY-deficiency. Additionally, data may indicate inefficient turnover of the CASA complex in tissues experiencing high tension. It is also shown that in vivo overexpression of recombinant KY is not sufficient to drive hypertrophy in normal mice, but may partially rescue fibre size in ky/ky mice

Improving detection of cystic fibrosis related liver disease using liver fibrosis assessment tools

BACKGROUND &amp; AIMS: Cystic Fibrosis related liver disease (CFLD) is the 3rd largest cause of death in Cystic Fibrosis (CF). As advances in pulmonary therapies have increased life-expectancy, CFLD has become more prevalent. Current guidelines may underdiagnose liver fibrosis, particularly in its early stages. Newer modalities for the assessment of fibrosis may provide a more accurate assessment. FibroScan is validated in assessing fibrosis for several aetiologies including alcohol and fatty liver, the CFLD cohort have an entirely different phenotype so the cut off values are not transferrable. We appraised fibrosis assessment tools to improve diagnosis of CFLD.METHODS: A prospective cohort (n = 114) of patients from the Manchester Adult Cystic Fibrosis Centre, UK were identified at annual assessment. Demographic data including co-morbidity, CFTR genotyping, biochemistry and imaging were used alongside current guidelines to group into CFLD and CF without evidence of liver disease. All patients underwent liver stiffness measurement (LSM) and assessment of serum-based fibrosis biomarker panels. A new diagnostic criterion was created and validated in a second, independent cohort.RESULTS: 12 of 114 patient classified as CFLD according to the European Cystic Fibrosis Society best practice guidelines. No specific risk factors for development of CFLD were identified. Liver enzymes were elevated in patients with CFLD. Serum biomarker panels did not improve diagnostic criteria. LSM accurately predicted CFLD. A new diagnostic criterion was proposed and validated in a separate cohort, accurately predicating CFLD in 10 of 32 patients (31 %).CONCLUSION: We present a cohort of patients with CF assessed for the presence of liver fibrosis using blood biomarkers and LSM based platforms. We propose a new, simplified diagnostic criteria, capable of accurately predicting liver disease in patients with CF.Clinical trials number: NCT04277819.</p