Key Points• T cells activated during GVHD increase their dependence upon fatty acid oxidation. • This dependence is not observed following acute activation or during normal immune reconstitution, suggesting novel therapeutic targets.Activated T cells require increased energy to proliferate and mediate effector functions, but the metabolic changes that occur in T cells following stimulation in vivo are poorly understood, particularly in the context of inflammation. We have previously shown that T cells activated during graft-versus-host disease (GVHD) primarily rely on oxidative phosphorylation to synthesize adenosine 59-triphosphate. Here, we demonstrate that alloreactive effector T cells (T eff ) use fatty acids (FAs) as a fuel source to support their in vivo activation. Alloreactive T cells increased FA transport, elevated levels of FA oxidation enzymes, up-regulated transcriptional coactivators to drive oxidative metabolism, and increased their rates of FA oxidation. Importantly, increases in FA transport and up-regulation of FA oxidation machinery occurred specifically in T cells during GVHD and were not seen in T eff following acute activation. Pharmacological blockade of FA oxidation decreased the survival of alloreactive T cells but did not influence the survival of T cells during normal immune reconstitution. These studies suggest that pathways controlling FA metabolism might serve as therapeutic targets to treat GVHD and other T-cell-mediated immune diseases. (Blood. 2013;122(18):3230-3237)

Tendon is a dense connective tissue that stores and transmits forces between muscles and bones. Cellular heterogeneity is increasingly recognized as an important factor in the biological basis of tissue homeostasis and disease, yet little is known about the diversity of cell types that populate tendon. To address this, we determined the heterogeneity of cell populations within mouse Achilles tendons using single-cell RNA sequencing. In assembling a transcriptomic atlas of Achilles tendons, we identified 11 distinct types of cells, including 3 previously undescribed populations of tendon fibroblasts. Prior studies have indicated that pericytes, which are found in the vasculature of tendons, could serve as a potential source of progenitor cells for adult tendon fibroblasts. Using trajectory inference analysis, we provide additional support for the notion that pericytes are likely to be at least one of the progenitor cell populations for the fibroblasts that compose adult tendons. We also modeled cell-cell interactions and identified previously undescribed ligand-receptor signaling interactions involved in tendon homeostasis. Our novel and interactive tendon atlas highlights previously underappreciated heterogeneity between and within tendon cell populations. The atlas also serves as a resource to further the understanding of tendon extracellular matrix assembly, maintenance, and in the design of therapies for tendinopathies.

Hedgehog (Hh) pathway inhibitors such as vismodegib are highly effective for treating basal cell carcinoma (BCC); however, residual tumor cells frequently persist and regenerate the primary tumor upon drug discontinuation. Here, we show that BCCs are organized into two molecularly and functionally distinct compartments. Whereas interior Hh/Notch suprabasal cells undergo apoptosis in response to vismodegib, peripheral Hh/Notch basal cells survive throughout treatment. Inhibiting Notch specifically promotes tumor persistence without causing drug resistance, while activating Notch is sufficient to regress already established lesions. Altogether, these findings suggest that the three-dimensional architecture of BCCs establishes a natural hierarchy of drug response in the tumor and that this hierarchy can be overcome, for better or worse, by modulating Notch.

Tendon injuries are a common clinical condition with limited treatment options. The cellular components of the innate immune system, such as neutrophils and macrophages, have been studied in tendon injuries. However, the adaptive immune system, comprising specialized lymphocytes, plays an important role in orchestrating the healing of numerous tissues, but less is known about these cells in tendon healing. To gain a greater understanding of the biological processes that regulate tendon healing, we determined how the cellular components of the adaptive and innate immune system respond to a tendon injury using two-month-old male mice. We observed that lymphatic vasculature is present in the epitenon and superficial regions of Achilles tendons, and that the lymphatics drain into the popliteal lymph node. We then created an acute Achilles tenotomy followed by repair, and collected tendons and popliteal lymph nodes 1, 2, and 4 wk after injury. Tendon injury resulted in a robust adaptive immune cell response that followed an initial innate immune cell response in tendons and lymph nodes. Monocytes, neutrophils, and macrophages initially accumulated at 1 wk after injury in tendons, while dendritic cells and CD4+ T cells peaked at 2 wk after injury. B cells and CD8+ T cells progressively increased over time. In parallel, immune cells of the popliteal lymph node demonstrated a similarly coordinated response to the injury. These results suggest that there is an adaptive immune response to tendon injury, and adaptive immune cells may play a role in regulating tendon healing. NEW & NOTEWORTHY While the innate immune system, consisting of macrophages and related hematopoietic cells, has been studied in tendon injury, less is known about the adaptive immune system. Using a mouse model of Achilles tendon tenotomy and repair, we observed an adaptive immune cell response, consisting of CD4+ and CD8+ T cells, and B cells, which occur through 4 wk after tendon injury. This response appeared to be coordinated by the draining popliteal lymph node.

The uppermost aspect of the hair follicle, known as the infundibulum or hair canal, provides a passageway for hair shaft egress and sebum secretion. Recent studies have indicated that the infundibulum and sebaceous ducts are lined by molecularly distinct differentiated cells expressing markers including Keratin 79 and Gata6. Here, we ablated Gata6 from the skin and observed dilation of both the hair canal and sebaceous ducts, independent of gender and hair cycle stage. Constitutive loss of Gata6 yielded only a mild delay in depilation-induced entry into anagen, while unperturbed mutant mice possessed overtly normal skin and hair. Furthermore, we noted that Keratin 79 and Gata6 expression and localization did not depend upon each other. Our findings implicate Gata6 in maintaining the upper hair follicle and suggest that regulation of this transcription factor may be compromised in pathologies such as acne or infundibular cystic diseases that are characterized by abnormal expansion of this follicular domain.