Macrophages are crucial in the body's inflammatory response, with tightly regulated functions for optimal immune system performance. Our study reveals that the RAS-p110α signalling pathway, known for its involvement in various biological processes and tumourigenesis, regulates two vital aspects of the inflammatory response in macrophages: the initial monocyte movement and later-stage lysosomal function. Disrupting this pathway, either in a mouse model or through drug intervention, hampers the inflammatory response, leading to delayed resolution and the development of more severe acute inflammatory reactions in live models. This discovery uncovers a previously unknown role of the p110α isoform in immune regulation within macrophages, offering insight into the complex mechanisms governing their function during inflammation and opening new avenues for modulating inflammatory responses.
© 2024, Rosell, Krygowska et al.

Mitochondria-ER membrane contact sites (MERCS) represent a fundamental ultrastructural feature underlying unique biochemistry and physiology in eukaryotic cells. The ER protein PDZD8 is required for the formation of MERCS in many cell types, however, its tethering partner on the outer mitochondrial membrane (OMM) is currently unknown. Here we identify the OMM protein FKBP8 as the tethering partner of PDZD8 using a combination of unbiased proximity proteomics, CRISPR-Cas9 endogenous protein tagging, Cryo-electron tomography, and correlative light-electron microscopy. Single molecule tracking reveals highly dynamic diffusion properties of PDZD8 along the ER membrane with significant pauses and captures at MERCS. Overexpression of FKBP8 is sufficient to narrow the ER-OMM distance, whereas independent versus combined deletions of these two proteins demonstrate their interdependence for MERCS formation. Furthermore, PDZD8 enhances mitochondrial complexity in a FKBP8-dependent manner. Our results identify a novel ER-mitochondria tethering complex that regulates mitochondrial morphology in mammalian cells.
© 2025. The Author(s).

The osteo-oto-hepato-enteric (O2HE) syndrome is a severe autosomal recessive disease ascribed to loss-of-function mutations in the Unc-45 myosin chaperone A (UNC45A) gene. The clinical spectrum includes bone fragility, hearing loss, cholestasis, and life-threatening diarrhea associated with microvillus inclusion disease-like enteropathy. Here, we present molecular and functional analysis of the UNC45A c.710T>C (p.Leu237Pro) missense variant, which revealed a unique pathogenicity compared with other genetic variants causing UNC45A deficiency. The UNC45A p.Leu237Pro mutant retained chaperone activity, prevented myosin aggregation, and supported proper nonmuscle myosin II (NMII) filament formation in patient fibroblasts and human osteosarcoma (U2OS) cells. However, the mutant formed atypically stable oligomers and prevented chaperone-myosin complex dissociation, thereby inhibiting NMII functions. Similar to biallelic UNC45A deficiency, this resulted in impaired intracellular trafficking, defective recycling, and abnormal retention of transferrin at various endocytic sites. In particular, coexpression of wild-type protein attenuated the pathogenic effects of the variant by inhibiting excessive oligomer formation. Our results elucidate the pathogenic mechanisms and recessive characteristics of this variant and may aid in the development of targeted therapies.

Abstract Niemann-Pick Disease (NPD) is a rare autosomal recessive lysosomal storage disorder (LSD) caused by the deficiency of acid sphingomyelinase (ASMD), which is encoded by the Smpd1 gene. ASMD impacts multiple organ systems in the body, including the cardiovascular system. This study is the first to characterize cardiac pathological changes in ASMD mice under baseline conditions, offering novel insights into the cardiac implications of NPD. Using histological analysis, biochemical assays, and echocardiography, we assessed cardiac pathological changes and function in Smpd1−/− mice compared to Smpd1+/+ littermate controls. Immunofluorescence and biochemical assays demonstrated that ASMD induced lysosomal dysfunction, as evidenced by the accumulation of lysosomal-associated membrane proteins, lysosomal protease, and autophagosomes in pericytes and cardiomyocytes. This lysosomal dysfunction was accompanied by pericytes and cardiomyocytes inflammation, characterized by increased expression of caspase1 and inflammatory cytokines, and infiltration of inflammatory cells in the cardiac tissues of Smpd1−/− mice. In addition, histological analysis revealed increased lipid deposition and cardiac steatosis, along with pericyte-to-myofibroblast transition (PMT) and interstitial fibrosis in Smpd1−/− mice. Moreover, echocardiography further demonstrated that Smpd1−/− mice developed coronary microvascular dysfunction (CMD), as evidenced by decreased coronary blood flow velocity and increased coronary arteriolar wall thickness. Additionally, these mice exhibited significant impairments in systolic and diastolic cardiac function, as shown by a reduced ejection fraction and prolonged left ventricular relaxation time constant (Tau value). These findings suggest that ASMD induces profound pathological changes and vascular dysfunction in the myocardium, potentially driven by mechanisms involving lysosomal dysfunction as well as both pericytes and cardiac inflammation.

Progranulin (PGRN) is a secretory precursor protein composed of 7.5 granulins (GRNs). Mutations in the PGRN-encoding gene Grn have been associated with neurodegenerative diseases. In our previous study, we found that Grn depletion in microglia disrupted glucose metabolism in mice fed a normal chow diet (NCD) but prevented the development of obesity in mice on a high-fat diet (HFD). Given that PGRN regulates lysosomal functions, we investigated lysosomal changes in the hypothalamus of mice with microglia-specific Grn depletion. Here we report that microglia-specific Grn depletion affects the lysosomes of hypothalamic proopiomelanocortin (POMC) neurons and microglia in diet-dependent fashion. Under NCD conditions, microglial Grn depletion led to increased lysosome mass, reduced lysosomal degradative capacity, and accumulation of lipofuscin and cytoplasmic TDP-43 in hypothalamic cells, indicative of lysosomal stress and dysfunction. In contrast, under HFD conditions, the absence of microglial Grn suppressed HFD-induced hypothalamic lysosomal stress. In cultured hypothalamic neurons and microglia, PGRN treatment enhanced lysosomal function, an effect inhibited by PGRN cleavage but restored when its cleavage was blocked. Since HFD feeding promotes the cleavage of hypothalamic PGRN into multi-GRNs and GRNs, the diet-dependent lysosomal changes observed in microglial Grn-depleted mice may be linked to PGRN cleavage. We also demonstrated that intracerebroventricular injection of bafilomycin, which induces lysosomal stress, resulted in microglial activation, inflammation, disrupted POMC neuronal circuitry, and impaired leptin signaling in the hypothalamus-common features of obesity. Our results indicate that microglial PGRN plays an important role in maintaining hypothalamic lysosomal function under healthy diet conditions, whereas increased cleavage of microglial PGRN in states of overnutrition disrupts hypothalamic lysosomal function, thereby fostering hypothalamic inflammation and obesity.
© 2025. The Author(s).