SUMMARY During endochondral bone development, the first osteoblasts differentiate in the perichondrium surrounding avascular cartilaginous rudiments; the source of trabecular osteoblasts inside the later bone is, however, unknown. Here, we generated tamoxifen-inducible transgenic mice bred to Rosa26R-LacZ reporter mice to follow the fates of stage-selective subsets of osteoblast lineage cells. Pulse-chase studies showed that osterix-expressing osteoblast precursors, labeled in the perichondrium prior to vascular invasion of the cartilage, give rise to trabecular osteoblasts, osteocytes, and stromal cells inside the developing bone. Throughout the translocation, some precursors were found to intimately associate with invading blood vessels, in pericyte-like fashion. A similar coinvasion occurs during endochondral healing of bone fractures. In contrast, perichondrial mature osteoblasts did not exhibit perivascular localization and remained in the outer cortex of developing bones. These findings reveal the specific involvement of immature osteoblast precursors in the coupled vascular and osteogenic transformation essential to endochondral bone development and repair.

Little is known about how pro-obesity diets regulate tissue stem and progenitor cell function. Here we find that high fat diet (HFD)-induced obesity augments the numbers and function of Lgr5+ intestinal stem-cells (ISCs) of the mammalian intestine. Mechanistically, HFD induces a robust peroxisome proliferator-activated receptor delta (PPAR-d) signature in intestinal stem and (non-ISC) progenitor cells, and pharmacologic activation of PPAR-d recapitulates the effects of a HFD on these cells. Like a HFD, ex vivo treatment of intestinal organoid cultures with fatty acid constituents of the HFD enhances the self-renewal potential of these organoid bodies in a PPAR-d dependent manner. Interestingly, HFD- and agonist-activated PPAR-d signaling endow organoid-initiating capacity to progenitors, and enforced PPAR-d signaling permits these progenitors to form in vivo tumors upon loss of the tumor suppressor Apc. These findings highlight how diet-modulated PPAR-d activation alters not only the function of intestinal stem and progenitor cells, but also their capacity to initiate tumors.

Activation of cellular stress response pathways to maintain metabolic homeostasis is emerging as a critical growth and survival mechanism in many cancers1. The pathogenesis of pancreatic ductal adenocarcinoma (PDA) requires high levels of autophagy2–4, a conserved self-degradative process5. However, the regulatory circuits that activate autophagy and reprogram PDA cell metabolism are unknown. We now show that autophagy induction in PDA occurs as part of a broader transcriptional program that coordinates activation of lysosome biogenesis and function, and nutrient scavenging, mediated by the MiT/TFE family transcription factors. In PDA cells, the MiT/TFE proteins6 – MITF, TFE3 and TFEB – are decoupled from regulatory mechanisms that control their cytoplasmic retention. Increased nuclear import in turn drives the expression of a coherent network of genes that induce high levels of lysosomal catabolic function essential for PDA growth. Unbiased global metabolite profiling reveals that MiT/TFE-dependent autophagy-lysosomal activation is specifically required to maintain intracellular amino acid (AA) pools. These results identify the MiT/TFE transcription factors as master regulators of metabolic reprogramming in pancreatic cancer and demonstrate activation of clearance pathways converging on the lysosome as a novel hallmark of aggressive malignancy.

SUMMARY How adult tissue stem and niche cells respond to the nutritional state of an organism is not well understood. Here, we find that Paneth cells, a key constituent of the mammalian intestinal stem cell (ISC) niche, augment stem cell function in response to calorie restriction (CR). CR acts by reducing mTOR complex 1 (mTORC1) signaling in Paneth cells, and the ISC-enhancing effects of CR can be mimicked by rapamycin. Calorie intake regulates mTORC1 in Paneth cells, but not ISCs, and forced mTORC1 activation in Paneth cells during CR abolishes their effects on ISCs. Finally, increased expression in Paneth cells of bone stromal antigen 1 (Bst-1), an ectoenzyme that produces the paracrine factor cyclic ADP ribose (cADPR), mediates the effects of CR and rapamycin on ISC function. Our findings establish that mTORC1 non-cell autonomously regulates stem cell self-renewal, and highlight a significant role of the mammalian intestinal niche in coupling stem cell function to organismal physiology.

We have established a line of transgenic mice expressing the A. victoria green fluorescent protein (GFP) under the control of the promoter for vascular endothelial growth factor (VEGF). Mice bearing the transgene show green cellular fluorescence around the healing margins and throughout the granulation tissue of superficial ulcerative wounds. Implantation of solid tumors in the transgenic mice leads to an accumulation of green fluorescence resulting from tumor induction of host VEGF promoter activity. With time, the fluorescent cells invade the tumor and can be seen throughout the tumor mass. Spontaneous mammary tumors induced by oncogene expression in the VEGF-GFP mouse show strong stromal, but not tumor, expression of GFP. In both wound and tumor models the predominant GFP-positive cells are fibroblasts. The finding that the VEGF promoter of nontransformed cells is strongly activated by the tumor microenvironment points to a need to analyze and understand stromal cell collaboration in tumor angiogenesis.

Human clinical trials in type 1 diabetes (T1D) patients using mesenchymal stem cells (MSC) are presently underway without prior validation in a mouse model for the disease. In response to this void, we characterized bone marrow-derived murine MSC for their ability to modulate immune responses in the context of T1D, as represented in NOD mice. In comparison to NOD mice, BALB/c-MSC mice were found to express higher levels of the negative costimulatory molecule PD-L1 and to promote a shift toward Th2-like responses in treated NOD mice. In addition, transfer of MSC from resistant strains (i.e., nonobese resistant mice or BALB/c), but not from NOD mice, delayed the onset of diabetes when administered to prediabetic NOD mice. The number of BALB/c-MSC trafficking to the pancreatic lymph nodes of NOD mice was higher than in NOD mice provided autologous NOD-MSC. Administration of BALB/c-MSC temporarily resulted in reversal of hyperglycemia in 90% of NOD mice (p = 0.002). Transfer of autologous NOD-MSC imparted no such therapeutic benefit. We also noted soft tissue and visceral tumors in NOD-MSC-treated mice, which were uniquely observed in this setting (i.e., no tumors were present with BALB/c- or nonobese resistant mice-MSC transfer). The importance of this observation remains to be explored in humans, as inbred mice such as NOD may be more susceptible to tumor formation. These data provide important preclinical data supporting the basis for further development of allogeneic MSC-based therapies for T1D and, potentially, for other autoimmune disorders.

Autoimmune pancreatitis (AIP) is a mass forming inflammatory pancreatobiliary-centric disease. Recent reports of multiorgan inflammatory mass forming lesions with increased numbers of IgG4 positive plasma cells suggest that AIP may have a systemic component. In this study, we explore the systemic nature of AIP, investigate the relevance of subtyping AIP, perform a systematic study of tissue IgG4 immunoperoxidase, and ultrastructurally evaluate the presence of immune complexes. Our study group consisted of 36 patients with AIP, 21 of whom underwent a Whipple procedure. On the basis of the pattern of inflammation, pancreatic involvement was subtyped as ductocentric (AIP-D) or lobulocentric (AIP-L). Extrapancreatic lesions included bile duct (n=3), salivary glands (n=3), lung (n=2), gallbladder (n=11), and kidney (n=4). Clinical and radiologic data was recorded. Immunohistochemistry for IgG4 was performed on both pancreatic and extrapancreatic tissues and the numbers of IgG4 positive plasma cells were semiquantitatively scored. A control cohort composed of pancreatic adenocarcinoma (n=19) and chronic pancreatitis-not otherwise specified (NOS) (n=14) was also evaluated. Eleven pancreatic specimens, including 2 cases of chronic pancreatitis-NOS and 4 kidneys were evaluated ultrastructurally. The pancreas, bile duct, gall bladder, salivary gland, kidney, and lung lesions were characterized by dense lymphoplasmacytic infiltrates with reactive fibroblasts and venulitis. IgG4 positive plasma cells were identified in all pancreatic and extrapancreatic lesions. The AIP cases showed significantly more pancreatic IgG4 positive plasma cells than chronic pancreatitis-NOS or adenocarcinoma (P=0.001). However, IgG4 positive cells were identified in 57.1% of chronic pancreatitis-NOS and 47.4% of ductal adenocarcinoma. Fifteen of 21 resected cases were classified as AIP-D, and 6 as AIP-L, the latter notably showing significantly more IgG4 positive plasma cells than the former (P=0.02). Additionally, clinical and radiologic differences emerged between the 2 groups. Ultrastructurally, electron dense deposits of immune complexes were identified in the basement membranes of 7 of the 9 AIP cases and in 3 of the 4 renal biopsies evaluated. AIP represents the pancreatic manifestation of a systemic autoimmune disease. Clinical and immunologic findings justify the recognition of pancreatic lobulocentric and ductocentric subtypes. Documentation of increased numbers of tissue IgG4 positive plasma cells, although not an entirely specific marker for AIP, may provide ancillary evidence for the diagnosis of a IgG4-related systemic disease.

Intermittent administration of parathyroid hormone (PTH) increases bone mass, at least in part, by increasing osteoblast number. One possible source of osteoblasts might be conversion of inactive lining cells to osteoblasts, and indirect evidence is consistent with this hypothesis. To better understand the possible effect of PTH on lining cell activation, a lineage tracing study was conducted using an inducible gene system. Dmp1-CreERt2 mice were crossed with ROSA26R reporter mice to render targeted mature osteoblasts and their descendents, lining cells and osteocytes, detectable by X-gal staining. Dmp1-CreERt2(+):ROSA26R mice were injected with 0.25 mg 4-OH-tamoxifen (4-OHTam) on postnatal day 3, 5, 7, 14, and 21. The animals were sacrificed on postnatal day 23, 33 or 43 (2, 12 or 22 days after the last 4-OHTam injection). On day 43, mice were challenged with a subcutaneous injection of human PTH (1–34, 80 μg/kg) or vehicle once daily for 3 days. By 22 days after the last 4-OHTam injection, most X-gal (+) cells on the periosteal surfaces of both the calvaria and tibia were flat. Moreover, bone formation rate and collagen I(α1) mRNA expression were decreased at day 43 compared to day 23. After 3 days of PTH injections, the thickness of X-gal (+) cells increased, as did their expression of osteocalcin and collagen I(α1) mRNA. Electron microscopy revealed X-gal-associated chromagen particles in both thin cells prior to PTH administration and cuboidal cells following PTH administration. These data support the hypothesis that intermittent PTH treatment can increase osteoblast number by converting lining cells to mature osteoblasts in vivo.