Acyl-CoA synthetase 3 promotes lipid droplet biogenesis in ER microdomains

Acyl-CoA synthetase 3 is recruited early to lipid droplet assembly sites on the ER, where it is required for efficient lipid droplet nucleation and lipid storage.

Control of lipid droplet (LD) nucleation and copy number are critical, yet poorly understood, processes. We use model peptides that shift from the endoplasmic reticulum (ER) to LDs in response to fatty acids to characterize the initial steps of LD formation occurring in lipid-starved cells. Initially, arriving lipids are rapidly packed in LDs that are resistant to starvation (pre-LDs). Pre-LDs are restricted ER microdomains with a stable core of neutral lipids. Subsequently, a first round of “emerging” LDs is nucleated, providing additional lipid storage capacity. Finally, in proportion to lipid concentration, new rounds of LDs progressively assemble. Confocal microscopy and electron tomography suggest that emerging LDs are nucleated in a limited number of ER microdomains after a synchronized stepwise process of protein gathering, lipid packaging, and recognition by Plin3 and Plin2. A comparative analysis demonstrates that the acyl-CoA synthetase 3 is recruited early to the assembly sites, where it is required for efficient LD nucleation and lipid storage.

AMPK activation promotes lipid droplet dispersion on detyrosinated microtubules to increase mitochondrial fatty acid oxidation

Lipid droplets (LDs) are intracellular organelles that provide fatty acids (FAs) to cellular processes including synthesis of membranes and production of metabolic energy. While known to move bidirectionally along microtubules (MTs), the role of LD motion and whether it facilitates interaction with other organelles are unclear. Here we show that during nutrient starvation, LDs and mitochondria relocate on detyrosinated MT from the cell centre to adopt a dispersed distribution. In the cell periphery, LD–mitochondria interactions increase and LDs efficiently supply FAs for mitochondrial beta-oxidation. This cellular adaptation requires the activation of the energy sensor AMPK, which in response to starvation simultaneously increases LD motion, reorganizes the network of detyrosinated MTs and activates mitochondria. In conclusion, we describe the existence of a specialized cellular network connecting the cellular energetic status and MT dynamics to coordinate the functioning of LDs and mitochondria during nutrient scarcity.

Lipid droplets (LDs) supply fatty acids to cellular processes and move bidirectionally on microtubules. Here the authors show that nutrient starvation causes dispersal of mitochondria and LD to the periphery of the cell along detyrosinated microtubules and increases LD–mitochondria interactions in an AMPK-dependent manner.

Caveolin-1 deficiency causes cholesterol-dependent mitochondrial dysfunction and apoptotic susceptibility

Caveolins (CAVs) are essential components of caveolae, plasma membrane invaginations with reduced fluidity, reflecting cholesterol accumulation. CAV proteins bind cholesterol, and CAV's ability to move between cellular compartments helps control intracellular cholesterol fluxes. In humans, CAV1 mutations result in lipodystrophy, cell transformation, and cancer. CAV1 gene-disrupted mice exhibit cardiovascular diseases, diabetes, cancer, atherosclerosis, and pulmonary fibrosis. The mechanism or mechanisms underlying these disparate effects are unknown, but our past work suggested that CAV1 deficiency might alter metabolism: CAV1(-/-) mice exhibit impaired liver regeneration unless supplemented with glucose, suggesting systemic inefficiencies requiring additional metabolic intermediates. Establishing a functional link between CAV1 and metabolism would provide a unifying theme to explain these myriad pathologies. Here we demonstrate that impaired proliferation and low survival with glucose restriction is a shortcoming of CAV1-deficient cells caused by impaired mitochondrial function. Without CAV1, free cholesterol accumulates in mitochondrial membranes, increasing membrane condensation and reducing efficiency of the respiratory chain and intrinsic antioxidant defense. Upon activation of oxidative phosphorylation, this promotes accumulation of reactive oxygen species, resulting in cell death. We confirm that this mitochondrial dysfunction predisposes CAV1-deficient animals to mitochondrial-related diseases such as steatohepatitis and neurodegeneration.

Spatial competition shapes the dynamic mutational landscape of normal esophageal epithelium

During aging, progenitor cells acquire mutations, which may generate clones that colonize the surrounding tissue. By middle age, normal human tissues, including the esophageal epithelium (EE), become a patchwork of mutant clones. Despite their relevance for understanding aging and cancer, the processes that underpin mutational selection in normal tissues remain poorly understood. Here, we investigated this issue in the esophageal epithelium of mutagen-treated mice. Deep sequencing identified numerous mutant clones with multiple genes under positive selection, including Notch1, Notch2 and Trp53, which are also selected in human esophageal epithelium. Transgenic lineage tracing revealed strong clonal competition that evolved over time. Clone dynamics were consistent with a simple model in which the proliferative advantage conferred by positively selected mutations depends on the nature of the neighboring cells. When clones with similar competitive fitness collide, mutant cell fate reverts towards homeostasis, a constraint that explains how selection operates in normal-appearing epithelium.

Mutant clones in normal epithelium outcompete and eliminate emerging tumours

Human epithelial tissues accumulate cancer-driver mutations with age1-9, yet tumour formation remains rare. The positive selection of these mutations suggests that they alter the behaviour and fitness of proliferating cells10-12. Thus, normal adult tissues become a patchwork of mutant clones competing for space and survival, with the fittest clones expanding by eliminating their less competitive neighbours11-14. However, little is known about how such dynamic competition in normal epithelia influences early tumorigenesis. Here we show that the majority of newly formed oesophageal tumours are eliminated through competition with mutant clones in the adjacent normal epithelium. We followed the fate of nascent, microscopic, pre-malignant tumours in a mouse model of oesophageal carcinogenesis and found that most were rapidly lost with no indication of tumour cell death, decreased proliferation or an anti-tumour immune response. However, deep sequencing of ten-day-old and one-year-old tumours showed evidence of selection on the surviving neoplasms. Induction of highly competitive clones in transgenic mice increased early tumour removal, whereas pharmacological inhibition of clonal competition reduced tumour loss. These results support a model in which survival of early neoplasms depends on their competitive fitness relative to that of mutant clones in the surrounding normal tissue. Mutant clones in normal epithelium have an unexpected anti-tumorigenic role in purging early tumours through cell competition, thereby preserving tissue integrity.

Outcompeting p53-Mutant Cells in the Normal Esophagus by Redox Manipulation

As humans age, normal tissues, such as the esophageal epithelium, become a patchwork of mutant clones. Some mutations are under positive selection, conferring a competitive advantage over wild-type cells. We speculated that altering the selective pressure on mutant cell populations may cause them to expand or contract. We tested this hypothesis by examining the effect of oxidative stress from low-dose ionizing radiation (LDIR) on wild-type and p53 mutant cells in the transgenic mouse esophagus. We found that LDIR drives wild-type cells to stop proliferating and differentiate. p53 mutant cells are insensitive to LDIR and outcompete wild-type cells following exposure. Remarkably, combining antioxidant treatment and LDIR reverses this effect, promoting wild-type cell proliferation and p53 mutant differentiation, reducing the p53 mutant population. Thus, p53-mutant cells can be depleted from the normal esophagus by redox manipulation, showing that external interventions may be used to alter the mutational landscape of an aging tissue.

Hydrophobic and basic domains target proteins to lipid droplets

In recent years, progress in the study of the lateral organization of the plasma membrane has led to the proposal that mammalian cells use two different organelles to store lipids: intracellular lipid droplets (LDs) and plasma membrane caveolae. Experimental evidence suggests that caveolin (CAV) may act as a sensitive lipid-organizing molecule that physically connects these two lipid-storing organelles. Here, we determine the sequences necessary for efficient sorting of CAV to LDs. We show that targeting is a process cooperatively mediated by two motifs. CAV's central hydrophobic domain (Hyd) anchors CAV to the endoplasmic reticulum (ER). Next, positively charged sequences (Pos-Seqs) mediate sorting of CAVs into LDs. Our findings were confirmed by identifying an equivalent, non-conserved but functionally interchangeable Pos-Seq in ALDI, a bona fide LD-resident protein. Using this information, we were able to retarget a cytosolic protein and convert it to an LD-resident protein. Further studies suggest three requirements for targeting via this mechanism: the positive charge of the Pos-Seq, physical proximity between Pos-Seq and Hyd and a precise spatial orientation between both motifs. The study uncovers remarkable similarities with the signals that target proteins to the membrane of mitochondria and peroxisomes.

A single-progenitor model as the unifying paradigm of epidermal and esophageal epithelial maintenance in mice

In adult skin epidermis and the epithelium lining the esophagus cells are constantly shed from the tissue surface and replaced by cell division. Tracking genetically labelled cells in transgenic mice has given insight into cell behavior, but conflicting models appear consistent with the results. Here, we use an additional transgenic assay to follow cell division in mouse esophagus and the epidermis at multiple body sites. We find that proliferating cells divide at a similar rate, and place bounds on the distribution cell cycle times. By including these results in a common analytic approach, we show that data from eight lineage tracing experiments is consistent with tissue maintenance by a single population of proliferating cells. The outcome of a given cell division is unpredictable but, on average, the likelihood of producing proliferating and differentiating cells is equal, ensuring cellular homeostasis. These findings are key to understanding squamous epithelial homeostasis and carcinogenesis.

Notch1 mutations drive clonal expansion in normal esophageal epithelium but impair tumor growth

NOTCH1 mutant clones occupy the majority of normal human esophagus by middle age but are comparatively rare in esophageal cancers, suggesting NOTCH1 mutations drive clonal expansion but impede carcinogenesis. Here we test this hypothesis. Sequencing NOTCH1 mutant clones in aging human esophagus reveals frequent biallelic mutations that block NOTCH1 signaling. In mouse esophagus, heterozygous Notch1 mutation confers a competitive advantage over wild-type cells, an effect enhanced by loss of the second allele. Widespread Notch1 loss alters transcription but has minimal effects on the epithelial structure and cell dynamics. In a carcinogenesis model, Notch1 mutations were less prevalent in tumors than normal epithelium. Deletion of Notch1 reduced tumor growth, an effect recapitulated by anti-NOTCH1 antibody treatment. Notch1 null tumors showed reduced proliferation. We conclude that Notch1 mutations in normal epithelium are beneficial as wild-type Notch1 favors tumor expansion. NOTCH1 blockade may have therapeutic potential in preventing esophageal squamous cancer.

Functional imaging of stress urinary incontinence

Stress urinary incontinence (SUI) is defined as an involuntary loss of urine during increases in intraabdominal pressure such as coughing or laughing. It is often a consequence of weakness of the pelvic floor. Treatment of SUI consists of pelvic floor muscle training with EMG-biofeedback (PFMT) or contraction-exercises, with voluntary pelvic contractions in order to strengthen the pelvic floor. We investigated neuroplastic changes comparing PFMT with EMG-biofeedback before and after training in ten female patients with SUI using event-related functional Magnetic Resonance Imaging (fMRI). After a 12-week training a more focused activation in the primary motor and somatosensory cortical representation sites of the lower urogenital tract was found. In addition, reductions in brain activation in the insula, right frontal operculum and the anterior cingulate cortex suggest changes in emotional arousal in micturition after treatment. These changes are related to clinical improvement documented by decreased number of incontinence episodes and increased EMG-activity of the pelvic floor muscles after training. The changes in EMG-activity were correlated with heightened BOLD responses in the primary motor and primary sensory cortical representation sites of the lower urogenital tract.

p53 mutation in normal esophagus promotes multiple stages of carcinogenesis but is constrained by clonal competition

Aging normal human oesophagus accumulates TP53 mutant clones. These are the origin of most oesophageal squamous carcinomas, in which biallelic TP53 disruption is almost universal. However, how p53 mutant clones expand and contribute to cancer development is unclear. Here we show that inducing the p53R245W mutant in single oesophageal progenitor cells in transgenic mice confers a proliferative advantage and clonal expansion but does not disrupt normal epithelial structure. Loss of the remaining p53 allele in mutant cells results in genomically unstable p53R245W/null epithelium with giant polyaneuploid cells and copy number altered clones. In carcinogenesis, p53 mutation does not initiate tumour formation, but tumours developing from areas with p53 mutation and LOH are larger and show extensive chromosomal instability compared to lesions arising in wild type epithelium. We conclude that p53 has distinct functions at different stages of carcinogenesis and that LOH within p53 mutant clones in normal epithelium is a critical step in malignant transformation.

Vesicocutaneous fistula 23 years after hip arthroplasty. A case report

Vesicocutaneous fistula after total hip replacement is a very rare but severe complication, which can appear months or years after operation. Intrapelvic cement (methylmethacrilate) spilling, loosening and dislocation of the prosthesis and infection are believed to be the cause of fistula formation. Only 4 cases of this kind of fistula have been reported in the literature. A new case of vesicocutaneous fistula is presented. The fistula developed 23 years after arthroplasty mainly because of hip-joint infection. Urinary tract symptoms caused by urinary infection appeared only few months earlier.

A portable forced oscillation device for respiratory home monitoring

The increase in the prevalence of chronic respiratory diseases has resulted in a rise in health services provided at home. The forced oscillation technique (FOT) proves to be a useful tool when it is desired to assess lung function noninvasively, and particularly for patients in whom spirometry cannot be applied. As no portable FOT device is currently available, the aim of this study was to design and test a portable FOT system for ambulatory and home care applications. The system devised is based on a microprocessor, which allows online computation of respiratory resistance (Rrs) and reactance (Xrs) and reliability indices. The portable device was compared with a conventional FOT system by using signals from 14 patients with chronic respiratory disease. This device has the same computation capabilities and flexibility as conventional FOT systems and meets the requirements for home application. Rrs (14.2 +/- 6.0 cmH2O x s x L(-1), mean +/- SD) and Xrs (-5.3 +/- 2.7 cmH2O x s x L(-1)) measured at 5 Hz by the portable system virtually coincided with those computed with the reference conventional FOT system: mean differences +/-SD were 0.074 +/- 0.025 and 0.005 +/- 0.009 cmH2O x s x L(-1), respectively. This portable forced oscillation technique device could be a useful tool for monitoring respiratory mechanics in ambulatory and home care applications.

Morphometric analysis of the fibroadipose tissue of the female pelvis

PURPOSE

The structure of the retroperitoneal connective tissue of the female pelvis was evaluated to determine whether its spatial arrangement may have a role in supporting the pelvic viscera.

MATERIALS AND METHODS

After in situ formalin fixation the pelvic viscera with the surrounding connective tissue were removed together with the pelvic floor from 18 female cadavers 48 to 68 years old. Serial macrosections of the bladder base, cervix, lower rectum and pelvic floor complex, cut in coronal (4 cases) and horizontal (10 cases) planes, were stained with azan-Mallory, and the remaining 4 were cut in the horizontal plane and plastinated using von Hagens E12 technique. Morphometry of the retroperitoneal connective tissue was performed using a computerized system for image analysis connected through a black and white television camera to an optic microscope. The diameters of the adipose lobules and density of the connective tissue were evaluated in the proximity of the visceral adventitia and the parietal pelvic fascia, respectively.

RESULTS

The retroperitoneal connective tissue of the female pelvis consists of varying amounts of adipose tissue divided into small lobules by thin connective laminae. These laminae are connected to the visceral and parietal layers of the pelvic fascia, and are closely connected to the vascular and nervous bundle sheaths crossing the pelvis. At the level of the sacrouterine and cardinal ligaments we were unable to find any connective ligamentous structure. Only an areolar tissue was seen, which after removal of the lipids demonstrated a fibrillar structure. The mean area of the adipose lobules was smaller (average of 1.41 mm.2) near the viscera with respect to the lateral retroperitoneal connective tissue (average of 1.73 mm.2) due to greater ramification of the connective laminae.

CONCLUSIONS

In the absence of real connective ligaments the retroperitoneal connective tissue forms a 3-dimensional network of thin connective laminae that are connected to the visceral adventitia, parietal layer of the pelvic fascia and neurovascular bundles crossing the pelvis. These connective laminae are bounding adipose lobules of different size (smaller near the viscera, larger at the periphery). Overall, the retroperitoneal connective tissue constitutes an anatomical structure that, beyond the functional limits of any individual ligament, may have supporting properties.

Self-sustaining long-term 3D epithelioid cultures reveal drivers of clonal expansion in esophageal epithelium

Aging epithelia are colonized by somatic mutations, which are subjected to selection influenced by intrinsic and extrinsic factors. The lack of suitable culture systems has slowed the study of this and other long-term biological processes. Here, we describe epithelioids, a facile, cost-effective method of culturing multiple mouse and human epithelia. Esophageal epithelioids self-maintain without passaging for at least 1 year, maintaining a three-dimensional structure with proliferative basal cells that differentiate into suprabasal cells, which eventually shed and retain genomic stability. Live imaging over 5 months showed that epithelioids replicate in vivo cell dynamics. Epithelioids support genetic manipulation and enable the study of mutant cell competition and selection in three-dimensional epithelia, and show how anti-cancer treatments modulate competition between transformed and wild-type cells. Finally, a targeted CRISPR-Cas9 screen shows that epithelioids recapitulate mutant gene selection in aging human esophagus and identifies additional drivers of clonal expansion, resolving the genetic networks underpinning competitive fitness.

Organismal metabolism regulates the expansion of oncogenic PIK3CA mutant clones in normal esophagus

Oncogenic PIK3CA mutations generate large clones in aging human esophagus. Here we investigate the behavior of Pik3ca mutant clones in the normal esophageal epithelium of transgenic mice. Expression of a heterozygous Pik3caH1047R mutation drives clonal expansion by tilting cell fate toward proliferation. CRISPR screening and inhibitor treatment of primary esophageal keratinocytes confirmed the PI3K-mTOR pathway increased mutant cell competitive fitness. The antidiabetic drug metformin reduced mutant cell advantage in vivo and in vitro. Conversely, metabolic conditions such as type 1 diabetes or diet-induced obesity enhanced the competitive fitness of Pik3caH1047R cells. Consistently, we found a higher density of PIK3CA gain-of-function mutations in the esophagus of individuals with high body mass index compared with those with normal weight. We conclude that the metabolic environment selectively influences the evolution of the normal epithelial mutational landscape. Clinically feasible interventions to even out signaling imbalances between wild-type and mutant cells may limit the expansion of oncogenic mutants in normal tissues.

Somatic Mutations in Normal Tissues: New Perspectives on Early Carcinogenesis

Normal tissues progressively acquire mutations. Some mutations are positively selected, driving clonal expansions that may colonize the majority of a tissue by old age. In several cases mutant clonal expansion is due to biasing stem cell fate toward proliferation. However, the expansionary phase is transient and is followed by reversion toward wild-type behavior so that normal tissue integrity is retained. Here we consider the implications of these findings for carcinogenesis. We propose that to be considered a cancer driver, a mutant gene should be more prevalent in tumors than the normal lineage from which it emerged. Cancer risk is not dependent on mutational burden, but rather may reflect the relative frequency of pro- and anti-oncogenic mutants within a tissue. Understanding the basis of mutant clonal advantage over wild-type cells allows interventions to halt the expansion or even deplete oncogenic mutants from normal tissue, potentially lowering cancer risk.

Expected final online publication date for the Annual Review of Cancer Biology, Volume 7 is April 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.