Biology subjects

Browning, L.

Publications and source records attributed to Browning, L..

3 recordsLinked to original sources

bioRxiv2023

2D and 3D multiplexed subcellular profiling of nuclear instability in human cancer

Nuclear atypia, including altered nuclear size, contour, and chromatin organization, is ubiquitous in cancer cells. Atypical primary nuclei and micronuclei can rupture during interphase; however, the frequency, causes, and consequences of nuclear rupture are unknown in most cancers. We demonstrate that nuclear envelope rupture is surprisingly common in many human cancers, particularly glioblastoma. Using highly-multiplexed 2D and super-resolution 3D-imaging of glioblastoma tissues and patient-derived xenografts and cells, we link primary nuclear rupture with reduced lamin A/C and micronuclear rupture with reduced lamin B1. Moreover, ruptured glioblastoma cells activate cGAS-STING-signaling involved in innate immunity. We observe that local patterning of cell states influences tumor spatial organization and is linked to both lamin expression and rupture frequency, with neural-progenitor-cell-like states exhibiting the lowest lamin A/C levels and greatest susceptibility to primary nuclear rupture. Our study reveals that nuclear instability is a core feature of cancer, and links nuclear integrity, cell state, and immune signaling.

cancer biology↗

bioRxiv2023

A neuron-specific microexon ablates the novel DNA-binding function of a histone H3K4me0 reader PHF21A

How cell-type-specific chromatin landscapes emerge and progress during metazoan ontogenesis remains an important question. Transcription factors are expressed in a cell-type-specific manner and recruit chromatin-regulatory machinery to specific genomic loci. In contrast, chromatin-regulatory proteins are expressed broadly and are assumed to exert the same intrinsic function across cell types. However, human genetics studies have revealed an unexpected vulnerability of neurodevelopment to chromatin factor mutations with unknown mechanisms. Here, we report that 14 chromatin regulators undergo evolutionary-conserved neuron-specific splicing events involving microexons. Of the 14 chromatin regulators, two are integral components of a histone H3K4 demethylase complex; the catalytic subunit LSD1 and an H3K4me0-reader protein PHF21A adopt neuron-specific forms. We found that canonical PHF21A (PHF21A-c) binds to DNA by AT-hook motif, and the neuronal counterpart PHF21A-n lacks this DNA-binding function yet maintains H3K4me0 recognition intact. In-vitro reconstitution of the canonical and neuronal PHF21A-LSD1 complexes identified the neuronal complex as a hypomorphic H3K4 demethylating machinery with reduced nucleosome engagement. Furthermore, an autism-associated PHF21A missense mutation, 1285 G>A, at the last nucleotide of the common exon immediately upstream of the neuronal microexon led to impaired splicing of PHF21A-n. Thus, ubiquitous chromatin regulatory complexes exert unique intrinsic functions in neurons via alternative splicing of their subunits and potentially contribute to faithful human brain development.

molecular biology↗

bioRxiv2022

Mesenchymal Stromal Cells Donate Mitochondria to Articular Chondrocytes Exposed to Mitochondrial, Environmental, and Mechanical Stress

Avascular soft tissues of the skeletal system, including articular cartilage, have limited healing capacity, in part due to their low metabolic activity. No drugs are available that can prevent or slow the development of osteoarthritis (OA) after joint injury. Therefore, mesenchymal stromal cell (MSC)-based regenerative therapies are increasingly common in the treatment of OA, but questions regarding their clinical efficacy and mechanisms of action remain unanswered. Our group recently reported that mitochondrial dysfunction is one of the earliest responses of cartilage to injury, resulting in chondrocyte death, extracellular matrix degeneration, and ultimately OA. MSCs have been found to rescue injured cells and improve healing by donating healthy mitochondria in highly metabolic tissues, but mitochondrial transfer has not been investigated in cartilage. Here, we demonstrate that MSCs transfer mitochondria to stressed chondrocytes in cell culture and in injured cartilage tissue. Conditions known induce chondrocyte mitochondrial dysfunction, including stimulation with rotenone/antimycin and hyperoxia, increased transfer. Stressed chondrocytes increased expression of genes related to inflammation and senescence, further supporting the link between mitochondrial dysfunction and transfer. MSC-chondrocyte mitochondrial transfer was blocked by non-specific and specific (connexin-43) gap-junction inhibition. When MSCs were exposed to mechanically injured cartilage they localized to areas of matrix damage and extended cellular processes deep into microcracks, delivering mitochondria to chondrocytes. This work provides insights into the chemical, environmental, and mechanical conditions that can elicit MSC-chondrocyte mitochondrial transfer in vitro and in situ, and our findings suggest a new potential role for MSC-based therapeutics after cartilage injury. Significance StatementRecent evidence suggests that although articular cartilage is avascular and relatively metabolically quiescent, acute injury induces chondrocyte mitochondrial dysfunction, driving cartilage degradation and OA. We present the first evidence that MSCs donate mitochondria to articular chondrocytes undergoing mitochondrial dysfunction in vitro and in situ. These findings support a new role for MSCs in the context of cartilage injury and OA, and intercellular mitochondrial transfer may represent a new biological approach to augment mitochondrial capacity in injured chondrocytes. This work establishes multiple experimental models to study MSC mitochondrial donation for the treatment of OA and related degenerative diseases of avascular orthopedic tissues.

cell biology↗