Introduction
Owing to their inherent hematopoiesis-supportive properties, mesenchymal
stromal cells (MSCs) are frequently used for the expansion of
hematopoietic stem cells (HSCs) in vitro [1,2]. In vitro expansion
is needed for cord blood (CB) samples as the HSCs obtained from one CB
unit are not sufficient for transplantation in an adult recipient
[3,4]. Likewise, the MSCs are co-infused with the HSCs into the
recipients to improve the success of stem cell transplantation
[5-8]. However, MSCs are sourced from various hematopoietic and
non-hematopoietic sources – the hematopoiesis-supportive properties of
MSCs isolated from non-hematopoietic sources might not be at par with
those isolated from the hematopoietic tissues. Donors’ age is also an
important factor governing the functionality of the MSCs [9,10]. Due
to their low number in the tissues, MSCs need a long-term in vitro
expansion – a process known to affect their regenerative potency
[11]. Considering all these possibilities, priming the MSCs with
various agents to boost their regenerative properties has become a focus
of several studies [12-16]. However, such manipulation needs to
be time efficient and cost-effective .
MSCs are typically characterized by their phenotypic and trilineage
differentiation ability [17]; however, these parameters do not
reflect their ability to support hematopoiesis. Long-term
culture-initiating-cell assay (LTC-IC) is routinely used to determine
the functionality of HSCs. Its readout not only helps estimate the
number of primitive HSCs present in the sample but also indirectly
reflects on the functionality of the stromal cells used as the feeder
layers. However, this assay takes about 10-12 weeks to complete, a
timeline that may not be suitable for a clinical setup. Hence, there is
a need to develop functional assays which can quickly judge the
hematopoiesis-supportive ability of the MSCs [18,19].
I have earlier shown that priming bone marrow-derived MSCs (BMSCs) with
Transforming Growth Factor β1 (TGFβ1) boosts their
hematopoiesis-supportive ability via AKT-eNOS axis [18]. In the
present study, I examined whether the BMSCs briefly primed with
pharmacological activators of downstream effectors of TGFβ1 pathway
could also boost their hematopoiesis-supportive ability. Indeed, I found
that short-term treatments of BMSCs with activators of protein kinase C
(PKC) and intracellular calcium [Ca2+]i and
various fibronectin (FN)- and integrin-specific bioactive peptides boost
the potency of BMSCs as evidenced by the formation of a significantly
higher number of colonies in semi-solid media and a rapid expansion of
CD34+ HSPCs from the BM-derived cells briefly
interacted with them. Such an approach comprising priming the BMSCs with
pharmacological compounds for a short duration and briefly exposing the
HSCs to them can be used in clinical settings to improve the efficacy of
stem cell transplantations. This concept would be helpful in other
regenerative medicine protocols after identifying suitable
pharmacological modulators giving desired effects on the target cells
[14,20].
These data demonstrate that it is possible to boost the potency of BMSCs
using various small molecule pharmacological agents targeting downstream
effectors of the TGFβ1 pathway. Also, the assays used in the present
study can be used as quick parameters to judge the functionality of
BMSCs to be used in clinical applications, and to identify compounds
having salutary effects on the hematopoiesis-supportive ability of
BMSCs.